Codechange: Store animated tile state in map to improve performance.

[openttd-github.git] / src / widget.cpp

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/** @file widget.cpp Handling of the default/simple widgets. */

#include "stdafx.h"
#include "core/backup_type.hpp"
#include "company_func.h"
#include "window_gui.h"
#include "viewport_func.h"
#include "zoom_func.h"
#include "strings_func.h"
#include "transparency.h"
#include "core/geometry_func.hpp"
#include "settings_type.h"
#include "querystring_gui.h"

#include "table/sprites.h"
#include "table/strings.h"
#include "table/string_colours.h"

#include "safeguards.h"

WidgetDimensions WidgetDimensions::scaled = {};

/**
 * Scale a RectPadding to GUI zoom level.
 * @param r RectPadding at ZOOM_BASE (traditional "normal" interface size).
 * @return RectPadding at #ZOOM_LVL_GUI (current interface size).
 */
static inline RectPadding ScaleGUITrad(const RectPadding &r)
{
        return {(uint8_t)ScaleGUITrad(r.left), (uint8_t)ScaleGUITrad(r.top), (uint8_t)ScaleGUITrad(r.right), (uint8_t)ScaleGUITrad(r.bottom)};
}

/**
 * Scale a Dimension to GUI zoom level.
 * @param d Dimension at ZOOM_BASE (traditional "normal" interface size).
 * @return Dimension at #ZOOM_LVL_GUI (current interface size).
 */
static inline Dimension ScaleGUITrad(const Dimension &dim)
{
        return {(uint)ScaleGUITrad(dim.width), (uint)ScaleGUITrad(dim.height)};
}

/**
 * Scale sprite size for GUI.
 * Offset is ignored.
 */
Dimension GetScaledSpriteSize(SpriteID sprid)
{
        Point offset;
        Dimension d = GetSpriteSize(sprid, &offset, ZOOM_LVL_NORMAL);
        d.width  -= offset.x;
        d.height -= offset.y;
        return ScaleGUITrad(d);
}

/**
 * Set up pre-scaled versions of Widget Dimensions.
 */
void SetupWidgetDimensions()
{
        WidgetDimensions::scaled.imgbtn       = ScaleGUITrad(WidgetDimensions::unscaled.imgbtn);
        WidgetDimensions::scaled.inset        = ScaleGUITrad(WidgetDimensions::unscaled.inset);
        WidgetDimensions::scaled.vscrollbar   = ScaleGUITrad(WidgetDimensions::unscaled.vscrollbar);
        WidgetDimensions::scaled.hscrollbar   = ScaleGUITrad(WidgetDimensions::unscaled.hscrollbar);
        if (_settings_client.gui.scale_bevels) {
                WidgetDimensions::scaled.bevel    = ScaleGUITrad(WidgetDimensions::unscaled.bevel);
        } else {
                WidgetDimensions::scaled.bevel    = WidgetDimensions::unscaled.bevel;
        }
        WidgetDimensions::scaled.fullbevel    = ScaleGUITrad(WidgetDimensions::unscaled.fullbevel);
        WidgetDimensions::scaled.framerect    = ScaleGUITrad(WidgetDimensions::unscaled.framerect);
        WidgetDimensions::scaled.frametext    = ScaleGUITrad(WidgetDimensions::unscaled.frametext);
        WidgetDimensions::scaled.matrix       = ScaleGUITrad(WidgetDimensions::unscaled.matrix);
        WidgetDimensions::scaled.shadebox     = ScaleGUITrad(WidgetDimensions::unscaled.shadebox);
        WidgetDimensions::scaled.stickybox    = ScaleGUITrad(WidgetDimensions::unscaled.stickybox);
        WidgetDimensions::scaled.debugbox     = ScaleGUITrad(WidgetDimensions::unscaled.debugbox);
        WidgetDimensions::scaled.defsizebox   = ScaleGUITrad(WidgetDimensions::unscaled.defsizebox);
        WidgetDimensions::scaled.resizebox    = ScaleGUITrad(WidgetDimensions::unscaled.resizebox);
        WidgetDimensions::scaled.closebox     = ScaleGUITrad(WidgetDimensions::unscaled.closebox);
        WidgetDimensions::scaled.captiontext  = ScaleGUITrad(WidgetDimensions::unscaled.captiontext);
        WidgetDimensions::scaled.dropdowntext = ScaleGUITrad(WidgetDimensions::unscaled.dropdowntext);
        WidgetDimensions::scaled.dropdownlist = ScaleGUITrad(WidgetDimensions::unscaled.dropdownlist);
        WidgetDimensions::scaled.modalpopup   = ScaleGUITrad(WidgetDimensions::unscaled.modalpopup);

        WidgetDimensions::scaled.vsep_normal  = ScaleGUITrad(WidgetDimensions::unscaled.vsep_normal);
        WidgetDimensions::scaled.vsep_wide    = ScaleGUITrad(WidgetDimensions::unscaled.vsep_wide);
        WidgetDimensions::scaled.hsep_normal  = ScaleGUITrad(WidgetDimensions::unscaled.hsep_normal);
        WidgetDimensions::scaled.hsep_wide    = ScaleGUITrad(WidgetDimensions::unscaled.hsep_wide);
        WidgetDimensions::scaled.hsep_indent  = ScaleGUITrad(WidgetDimensions::unscaled.hsep_indent);
}

/**
 * Calculate x and y coordinates for an aligned object within a window.
 * @param r     Rectangle of the widget to be drawn in.
 * @param d     Dimension of the object to be drawn.
 * @param align Alignment of the object.
 * @return A point containing the position at which to draw.
 */
static inline Point GetAlignedPosition(const Rect &r, const Dimension &d, StringAlignment align)
{
        Point p;
        /* In case we have a RTL language we swap the alignment. */
        if (!(align & SA_FORCE) && _current_text_dir == TD_RTL && (align & SA_HOR_MASK) != SA_HOR_CENTER) align ^= SA_RIGHT;
        switch (align & SA_HOR_MASK) {
                case SA_LEFT:       p.x = r.left; break;
                case SA_HOR_CENTER: p.x = CenterBounds(r.left, r.right, d.width); break;
                case SA_RIGHT:      p.x = r.right + 1 - d.width; break;
                default: NOT_REACHED();
        }
        switch (align & SA_VERT_MASK) {
                case SA_TOP:         p.y = r.top; break;
                case SA_VERT_CENTER: p.y = CenterBounds(r.top, r.bottom, d.height); break;
                case SA_BOTTOM:      p.y = r.bottom + 1 - d.height; break;
                default: NOT_REACHED();
        }
        return p;
}

/**
 * Compute the vertical position of the draggable part of scrollbar
 * @param sb     Scrollbar list data
 * @param top    Top position of the scrollbar (top position of the up-button)
 * @param bottom Bottom position of the scrollbar (bottom position of the down-button)
 * @param horizontal Whether the scrollbar is horizontal or not
 * @return A Point, with x containing the top coordinate of the draggable part, and
 *                       y containing the bottom coordinate of the draggable part
 */
static Point HandleScrollbarHittest(const Scrollbar *sb, int top, int bottom, bool horizontal)
{
        /* Base for reversion */
        int rev_base = top + bottom;
        int button_size;
        if (horizontal) {
                button_size = NWidgetScrollbar::GetHorizontalDimension().width;
        } else {
                button_size = NWidgetScrollbar::GetVerticalDimension().height;
        }
        top += button_size;    // top    points to just below the up-button
        bottom -= button_size; // bottom points to top of the down-button

        int count = sb->GetCount();
        int cap = sb->GetCapacity();

        if (count > cap) {
                int height = (bottom - top);
                int slider_height = std::max(button_size, cap * height / count);
                height -= slider_height;

                top += height * sb->GetPosition() / (count - cap);
                bottom = top + slider_height;
        }

        Point pt;
        if (horizontal && _current_text_dir == TD_RTL) {
                pt.x = rev_base - bottom;
                pt.y = rev_base - top;
        } else {
                pt.x = top;
                pt.y = bottom;
        }
        return pt;
}

/**
 * Compute new position of the scrollbar after a click and updates the window flags.
 * @param w   Window on which a scroll was performed.
 * @param sb  Scrollbar
 * @param mi  Minimum coordinate of the scroll bar.
 * @param ma  Maximum coordinate of the scroll bar.
 * @param x   The X coordinate of the mouse click.
 * @param y   The Y coordinate of the mouse click.
 */
static void ScrollbarClickPositioning(Window *w, NWidgetScrollbar *sb, int x, int y, int mi, int ma)
{
        int pos;
        int button_size;
        bool rtl = false;
        bool changed = false;

        if (sb->type == NWID_HSCROLLBAR) {
                pos = x;
                rtl = _current_text_dir == TD_RTL;
                button_size = NWidgetScrollbar::GetHorizontalDimension().width;
        } else {
                pos = y;
                button_size = NWidgetScrollbar::GetVerticalDimension().height;
        }
        if (pos < mi + button_size) {
                /* Pressing the upper button? */
                SetBit(sb->disp_flags, NDB_SCROLLBAR_UP);
                if (_scroller_click_timeout <= 1) {
                        _scroller_click_timeout = 3;
                        changed = sb->UpdatePosition(rtl ? 1 : -1);
                }
                w->mouse_capture_widget = sb->index;
        } else if (pos >= ma - button_size) {
                /* Pressing the lower button? */
                SetBit(sb->disp_flags, NDB_SCROLLBAR_DOWN);

                if (_scroller_click_timeout <= 1) {
                        _scroller_click_timeout = 3;
                        changed = sb->UpdatePosition(rtl ? -1 : 1);
                }
                w->mouse_capture_widget = sb->index;
        } else {
                Point pt = HandleScrollbarHittest(sb, mi, ma, sb->type == NWID_HSCROLLBAR);

                if (pos < pt.x) {
                        changed = sb->UpdatePosition(rtl ? 1 : -1, Scrollbar::SS_BIG);
                } else if (pos > pt.y) {
                        changed = sb->UpdatePosition(rtl ? -1 : 1, Scrollbar::SS_BIG);
                } else {
                        _scrollbar_start_pos = pt.x - mi - button_size;
                        _scrollbar_size = ma - mi - button_size * 2 - (pt.y - pt.x);
                        w->mouse_capture_widget = sb->index;
                        _cursorpos_drag_start = _cursor.pos;
                }
        }

        if (changed) {
                /* Position changed so refresh the window */
                w->SetDirty();
        } else {
                /* No change so only refresh this scrollbar */
                sb->SetDirty(w);
        }
}

/**
 * Special handling for the scrollbar widget type.
 * Handles the special scrolling buttons and other scrolling.
 * @param w Window on which a scroll was performed.
 * @param nw Pointer to the scrollbar widget.
 * @param x The X coordinate of the mouse click.
 * @param y The Y coordinate of the mouse click.
 */
void ScrollbarClickHandler(Window *w, NWidgetCore *nw, int x, int y)
{
        int mi, ma;

        if (nw->type == NWID_HSCROLLBAR) {
                mi = nw->pos_x;
                ma = nw->pos_x + nw->current_x;
        } else {
                mi = nw->pos_y;
                ma = nw->pos_y + nw->current_y;
        }
        NWidgetScrollbar *scrollbar = dynamic_cast<NWidgetScrollbar*>(nw);
        assert(scrollbar != nullptr);
        ScrollbarClickPositioning(w, scrollbar, x, y, mi, ma);
}

/**
 * Returns the index for the widget located at the given position
 * relative to the window. It includes all widget-corner pixels as well.
 * @param *w Window to look inside
 * @param  x The Window client X coordinate
 * @param  y The Window client y coordinate
 * @return A widget index, or -1 if no widget was found.
 */
WidgetID GetWidgetFromPos(const Window *w, int x, int y)
{
        NWidgetCore *nw = w->nested_root->GetWidgetFromPos(x, y);
        return (nw != nullptr) ? nw->index : -1;
}

/**
 * Draw frame rectangle.
 * @param left   Left edge of the frame
 * @param top    Top edge of the frame
 * @param right  Right edge of the frame
 * @param bottom Bottom edge of the frame
 * @param colour Colour table to use. @see Colours
 * @param flags  Flags controlling how to draw the frame. @see FrameFlags
 */
void DrawFrameRect(int left, int top, int right, int bottom, Colours colour, FrameFlags flags)
{
        assert(colour < COLOUR_END);

        uint dark         = GetColourGradient(colour, SHADE_DARK);
        uint medium_dark  = GetColourGradient(colour, SHADE_LIGHT);
        uint medium_light = GetColourGradient(colour, SHADE_LIGHTER);
        uint light        = GetColourGradient(colour, SHADE_LIGHTEST);

        if (flags & FR_TRANSPARENT) {
                GfxFillRect(left, top, right, bottom, PALETTE_TO_TRANSPARENT, FILLRECT_RECOLOUR);
        } else {
                uint interior;

                Rect outer = {left, top, right, bottom};                   // Outside rectangle
                Rect inner = outer.Shrink(WidgetDimensions::scaled.bevel); // Inside rectangle

                if (flags & FR_LOWERED) {
                        GfxFillRect(outer.left,      outer.top,        inner.left - 1,  outer.bottom, dark);   // Left
                        GfxFillRect(inner.left,      outer.top,        outer.right,     inner.top - 1, dark);  // Top
                        GfxFillRect(inner.right + 1, inner.top,        outer.right,     inner.bottom,  light); // Right
                        GfxFillRect(inner.left,      inner.bottom + 1, outer.right,     outer.bottom, light);  // Bottom
                        interior = (flags & FR_DARKENED ? medium_dark : medium_light);
                } else {
                        GfxFillRect(outer.left,      outer.top,        inner.left - 1, inner.bottom,  light); // Left
                        GfxFillRect(inner.left,      outer.top,        inner.right,    inner.top - 1, light); // Top
                        GfxFillRect(inner.right + 1, outer.top,        outer.right,    inner.bottom,  dark);  // Right
                        GfxFillRect(outer.left,      inner.bottom + 1, outer.right,    outer.bottom, dark);   // Bottom
                        interior = medium_dark;
                }
                if (!(flags & FR_BORDERONLY)) {
                        GfxFillRect(inner.left,  inner.top, inner.right, inner.bottom, interior); // Inner
                }
        }
}

void DrawSpriteIgnorePadding(SpriteID img, PaletteID pal, const Rect &r, StringAlignment align)
{
        Point offset;
        Dimension d = GetSpriteSize(img, &offset);
        d.width  -= offset.x;
        d.height -= offset.y;

        Point p = GetAlignedPosition(r, d, align);
        DrawSprite(img, pal, p.x - offset.x, p.y - offset.y);
}

/**
 * Draw an image button.
 * @param r       Rectangle of the button.
 * @param type    Widget type (#WWT_IMGBTN or #WWT_IMGBTN_2).
 * @param colour  Colour of the button.
 * @param clicked Button is clicked.
 * @param img     Sprite to draw.
 * @param align   Alignment of the sprite.
 */
static inline void DrawImageButtons(const Rect &r, WidgetType type, Colours colour, bool clicked, SpriteID img, StringAlignment align)
{
        assert(img != 0);
        DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FR_LOWERED : FR_NONE);

        if ((type & WWT_MASK) == WWT_IMGBTN_2 && clicked) img++; // Show different image when clicked for #WWT_IMGBTN_2.
        DrawSpriteIgnorePadding(img, PAL_NONE, r, align);
}

/**
 * Draw the label-part of a widget.
 * @param r       Rectangle of the label background.
 * @param type    Widget type (#WWT_TEXTBTN, #WWT_TEXTBTN_2, or #WWT_LABEL).
 * @param clicked Label is clicked.
 * @param colour  Colour of the text.
 * @param str     Text to draw.
 * @param align   Alignment of the text.
 * @param fs      Font size of the text.
 */
static inline void DrawLabel(const Rect &r, WidgetType type, bool clicked, TextColour colour, StringID str, StringAlignment align, FontSize fs)
{
        if (str == STR_NULL) return;
        if ((type & WWT_MASK) == WWT_TEXTBTN_2 && clicked) str++;
        Dimension d = GetStringBoundingBox(str, fs);
        Point p = GetAlignedPosition(r, d, align);
        DrawString(r.left, r.right, p.y, str, colour, align, false, fs);
}

/**
 * Draw text.
 * @param r      Rectangle of the background.
 * @param colour Colour of the text.
 * @param str    Text to draw.
 * @param align  Alignment of the text.
 * @param fs     Font size of the text.
 */
static inline void DrawText(const Rect &r, TextColour colour, StringID str, StringAlignment align, FontSize fs)
{
        Dimension d = GetStringBoundingBox(str, fs);
        Point p = GetAlignedPosition(r, d, align);
        if (str != STR_NULL) DrawString(r.left, r.right, p.y, str, colour, align, false, fs);
}

/**
 * Draw an inset widget.
 * @param r           Rectangle of the background.
 * @param colour      Colour of the inset.
 * @param text_colour Colour of the text.
 * @param str         Text to draw.
 * @param align       Alignment of the text.
 * @param fs          Font size of the text.
 */
static inline void DrawInset(const Rect &r, Colours colour, TextColour text_colour, StringID str, StringAlignment align, FontSize fs)
{
        DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, FR_LOWERED | FR_DARKENED);
        if (str != STR_NULL) DrawString(r.Shrink(WidgetDimensions::scaled.inset), str, text_colour, align, false, fs);
}

/**
 * Draw a matrix widget.
 * @param r       Rectangle of the matrix background.
 * @param colour  Colour of the background.
 * @param clicked Matrix is rendered lowered.
 * @param data    Data of the widget, number of rows and columns of the widget.
 * @param resize_x Matrix resize unit size.
 * @param resize_y Matrix resize unit size.
 */
static inline void DrawMatrix(const Rect &r, Colours colour, bool clicked, uint16_t data, uint resize_x, uint resize_y)
{
        DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FR_LOWERED : FR_NONE);

        int num_columns = GB(data, MAT_COL_START, MAT_COL_BITS);  // Lower 8 bits of the widget data: Number of columns in the matrix.
        int column_width; // Width of a single column in the matrix.
        if (num_columns == 0) {
                column_width = resize_x;
                num_columns = r.Width() / column_width;
        } else {
                column_width = r.Width() / num_columns;
        }

        int num_rows = GB(data, MAT_ROW_START, MAT_ROW_BITS); // Upper 8 bits of the widget data: Number of rows in the matrix.
        int row_height; // Height of a single row in the matrix.
        if (num_rows == 0) {
                row_height = resize_y;
                num_rows = r.Height() / row_height;
        } else {
                row_height = r.Height() / num_rows;
        }

        int col = GetColourGradient(colour, SHADE_LIGHTER);

        int x = r.left;
        for (int ctr = num_columns; ctr > 1; ctr--) {
                x += column_width;
                GfxFillRect(x, r.top + WidgetDimensions::scaled.bevel.top, x + WidgetDimensions::scaled.bevel.left - 1, r.bottom - WidgetDimensions::scaled.bevel.bottom, col);
        }

        x = r.top;
        for (int ctr = num_rows; ctr > 1; ctr--) {
                x += row_height;
                GfxFillRect(r.left + WidgetDimensions::scaled.bevel.left, x, r.right - WidgetDimensions::scaled.bevel.right, x + WidgetDimensions::scaled.bevel.top - 1, col);
        }

        col = GetColourGradient(colour, SHADE_NORMAL);

        x = r.left - 1;
        for (int ctr = num_columns; ctr > 1; ctr--) {
                x += column_width;
                GfxFillRect(x - WidgetDimensions::scaled.bevel.right + 1, r.top + WidgetDimensions::scaled.bevel.top, x, r.bottom - WidgetDimensions::scaled.bevel.bottom, col);
        }

        x = r.top - 1;
        for (int ctr = num_rows; ctr > 1; ctr--) {
                x += row_height;
                GfxFillRect(r.left + WidgetDimensions::scaled.bevel.left, x - WidgetDimensions::scaled.bevel.bottom + 1, r.right - WidgetDimensions::scaled.bevel.right, x, col);
        }
}

/**
 * Draw a vertical scrollbar.
 * @param r            Rectangle of the scrollbar widget.
 * @param colour       Colour of the scrollbar widget.
 * @param up_clicked   Up-arrow is clicked.
 * @param bar_dragged  Bar is dragged.
 * @param down_clicked Down-arrow is clicked.
 * @param scrollbar    Scrollbar size, offset, and capacity information.
 */
static inline void DrawVerticalScrollbar(const Rect &r, Colours colour, bool up_clicked, bool bar_dragged, bool down_clicked, const Scrollbar *scrollbar)
{
        int height = NWidgetScrollbar::GetVerticalDimension().height;

        /* draw up/down buttons */
        DrawImageButtons(r.WithHeight(height, false),  NWID_VSCROLLBAR, colour, up_clicked,   SPR_ARROW_UP,   SA_CENTER);
        DrawImageButtons(r.WithHeight(height, true),   NWID_VSCROLLBAR, colour, down_clicked, SPR_ARROW_DOWN, SA_CENTER);

        int c1 = GetColourGradient(colour, SHADE_DARK);
        int c2 = GetColourGradient(colour, SHADE_LIGHTEST);

        /* draw "shaded" background */
        GfxFillRect(r.left, r.top + height, r.right, r.bottom - height, c2);
        GfxFillRect(r.left, r.top + height, r.right, r.bottom - height, c1, FILLRECT_CHECKER);

        /* track positions. These fractions are based on original 1x dimensions, but scale better. */
        int left  = r.left + r.Width() * 3 / 11; /*  left track is positioned 3/11ths from the left */
        int right = r.left + r.Width() * 8 / 11; /* right track is positioned 8/11ths from the left */
        const uint8_t bl = WidgetDimensions::scaled.bevel.left;
        const uint8_t br = WidgetDimensions::scaled.bevel.right;

        /* draw shaded lines */
        GfxFillRect(left - bl,  r.top + height, left       - 1, r.bottom - height, c1);
        GfxFillRect(left,       r.top + height, left + br  - 1, r.bottom - height, c2);
        GfxFillRect(right - bl, r.top + height, right      - 1, r.bottom - height, c1);
        GfxFillRect(right,      r.top + height, right + br - 1, r.bottom - height, c2);

        Point pt = HandleScrollbarHittest(scrollbar, r.top, r.bottom, false);
        DrawFrameRect(r.left, pt.x, r.right, pt.y, colour, bar_dragged ? FR_LOWERED : FR_NONE);
}

/**
 * Draw a horizontal scrollbar.
 * @param r             Rectangle of the scrollbar widget.
 * @param colour        Colour of the scrollbar widget.
 * @param left_clicked  Left-arrow is clicked.
 * @param bar_dragged   Bar is dragged.
 * @param right_clicked Right-arrow is clicked.
 * @param scrollbar     Scrollbar size, offset, and capacity information.
 */
static inline void DrawHorizontalScrollbar(const Rect &r, Colours colour, bool left_clicked, bool bar_dragged, bool right_clicked, const Scrollbar *scrollbar)
{
        int width = NWidgetScrollbar::GetHorizontalDimension().width;

        DrawImageButtons(r.WithWidth(width, false), NWID_HSCROLLBAR, colour, left_clicked,  SPR_ARROW_LEFT,  SA_CENTER);
        DrawImageButtons(r.WithWidth(width, true),  NWID_HSCROLLBAR, colour, right_clicked, SPR_ARROW_RIGHT, SA_CENTER);

        int c1 = GetColourGradient(colour, SHADE_DARK);
        int c2 = GetColourGradient(colour, SHADE_LIGHTEST);

        /* draw "shaded" background */
        GfxFillRect(r.left + width, r.top, r.right - width, r.bottom, c2);
        GfxFillRect(r.left + width, r.top, r.right - width, r.bottom, c1, FILLRECT_CHECKER);

        /* track positions. These fractions are based on original 1x dimensions, but scale better. */
        int top    = r.top + r.Height() * 3 / 11; /*    top track is positioned 3/11ths from the top */
        int bottom = r.top + r.Height() * 8 / 11; /* bottom track is positioned 8/11ths from the top */
        const uint8_t bt = WidgetDimensions::scaled.bevel.top;
        const uint8_t bb = WidgetDimensions::scaled.bevel.bottom;

        /* draw shaded lines */
        GfxFillRect(r.left + width, top - bt,    r.right - width, top         - 1, c1);
        GfxFillRect(r.left + width, top,         r.right - width, top + bb    - 1, c2);
        GfxFillRect(r.left + width, bottom - bt, r.right - width, bottom      - 1, c1);
        GfxFillRect(r.left + width, bottom,      r.right - width, bottom + bb - 1, c2);

        /* draw actual scrollbar */
        Point pt = HandleScrollbarHittest(scrollbar, r.left, r.right, true);
        DrawFrameRect(pt.x, r.top, pt.y, r.bottom, colour, bar_dragged ? FR_LOWERED : FR_NONE);
}

/**
 * Draw a frame widget.
 * @param r           Rectangle of the frame.
 * @param colour      Colour of the frame.
 * @param text_colour Colour of the text.
 * @param str         Text of the frame.
 * @param align       Alignment of the text in the frame.
 * @param fs          Font size of the text.
 */
static inline void DrawFrame(const Rect &r, Colours colour, TextColour text_colour, StringID str, StringAlignment align, FontSize fs)
{
        int x2 = r.left; // by default the left side is the left side of the widget

        if (str != STR_NULL) x2 = DrawString(r.left + WidgetDimensions::scaled.frametext.left, r.right - WidgetDimensions::scaled.frametext.right, r.top, str, text_colour, align, false, fs);

        int c1 = GetColourGradient(colour, SHADE_DARK);
        int c2 = GetColourGradient(colour, SHADE_LIGHTEST);

        /* If the frame has text, adjust the top bar to fit half-way through */
        Rect inner = r.Shrink(ScaleGUITrad(1));
        if (str != STR_NULL) inner.top = r.top + GetCharacterHeight(FS_NORMAL) / 2;

        Rect outer  = inner.Expand(WidgetDimensions::scaled.bevel);
        Rect inside = inner.Shrink(WidgetDimensions::scaled.bevel);

        if (_current_text_dir == TD_LTR) {
                /* Line from upper left corner to start of text */
                GfxFillRect(outer.left, outer.top, r.left + WidgetDimensions::scaled.frametext.left - WidgetDimensions::scaled.bevel.left - 1, inner.top  - 1, c1);
                GfxFillRect(inner.left, inner.top, r.left + WidgetDimensions::scaled.frametext.left - WidgetDimensions::scaled.bevel.left - 1, inside.top - 1, c2);

                /* Line from end of text to upper right corner */
                GfxFillRect(x2 + WidgetDimensions::scaled.bevel.right, outer.top, inner.right,  inner.top  - 1, c1);
                GfxFillRect(x2 + WidgetDimensions::scaled.bevel.right, inner.top, inside.right, inside.top - 1, c2);
        } else {
                /* Line from upper left corner to start of text */
                GfxFillRect(outer.left, outer.top, x2 - WidgetDimensions::scaled.bevel.left - 1, inner.top  - 1, c1);
                GfxFillRect(inner.left, inner.top, x2 - WidgetDimensions::scaled.bevel.left - 1, inside.top - 1, c2);

                /* Line from end of text to upper right corner */
                GfxFillRect(r.right - WidgetDimensions::scaled.frametext.right + WidgetDimensions::scaled.bevel.right, outer.top, inner.right,  inner.top  - 1, c1);
                GfxFillRect(r.right - WidgetDimensions::scaled.frametext.right + WidgetDimensions::scaled.bevel.right, inner.top, inside.right, inside.top - 1, c2);
        }

        /* Line from upper left corner to bottom left corner */
        GfxFillRect(outer.left, inner.top,  inner.left  - 1, inner.bottom,  c1);
        GfxFillRect(inner.left, inside.top, inside.left - 1, inside.bottom, c2);

        /* Line from upper right corner to bottom right corner */
        GfxFillRect(inside.right + 1, inner.top, inner.right, inside.bottom, c1);
        GfxFillRect(inner.right  + 1, outer.top, outer.right, inner.bottom,  c2);

        /* Line from bottom left corner to bottom right corner */
        GfxFillRect(inner.left, inside.bottom + 1, inner.right, inner.bottom, c1);
        GfxFillRect(outer.left, inner.bottom  + 1, outer.right, outer.bottom, c2);
}

/**
 * Draw a shade box.
 * @param r       Rectangle of the box.
 * @param colour  Colour of the shade box.
 * @param clicked Box is lowered.
 */
static inline void DrawShadeBox(const Rect &r, Colours colour, bool clicked)
{
        DrawImageButtons(r, WWT_SHADEBOX, colour, clicked, clicked ? SPR_WINDOW_SHADE: SPR_WINDOW_UNSHADE, SA_CENTER);
}

/**
 * Draw a sticky box.
 * @param r       Rectangle of the box.
 * @param colour  Colour of the sticky box.
 * @param clicked Box is lowered.
 */
static inline void DrawStickyBox(const Rect &r, Colours colour, bool clicked)
{
        DrawImageButtons(r, WWT_STICKYBOX, colour, clicked, clicked ? SPR_PIN_UP : SPR_PIN_DOWN, SA_CENTER);
}

/**
 * Draw a defsize box.
 * @param r       Rectangle of the box.
 * @param colour  Colour of the defsize box.
 * @param clicked Box is lowered.
 */
static inline void DrawDefSizeBox(const Rect &r, Colours colour, bool clicked)
{
        DrawImageButtons(r, WWT_DEFSIZEBOX, colour, clicked, SPR_WINDOW_DEFSIZE, SA_CENTER);
}

/**
 * Draw a NewGRF debug box.
 * @param r       Rectangle of the box.
 * @param colour  Colour of the debug box.
 * @param clicked Box is lowered.
 */
static inline void DrawDebugBox(const Rect &r, Colours colour, bool clicked)
{
        DrawImageButtons(r, WWT_DEBUGBOX, colour, clicked, SPR_WINDOW_DEBUG, SA_CENTER);
}

/**
 * Draw a resize box.
 * @param r       Rectangle of the box.
 * @param colour  Colour of the resize box.
 * @param at_left Resize box is at left-side of the window,
 * @param clicked Box is lowered.
 * @param bevel   Draw bevel iff set.
 */
static inline void DrawResizeBox(const Rect &r, Colours colour, bool at_left, bool clicked, bool bevel)
{
        if (bevel) {
                DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, (clicked) ? FR_LOWERED : FR_NONE);
        } else if (clicked) {
                GfxFillRect(r.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(colour, SHADE_LIGHTER));
        }
        DrawSpriteIgnorePadding(at_left ? SPR_WINDOW_RESIZE_LEFT : SPR_WINDOW_RESIZE_RIGHT, PAL_NONE, r.Shrink(ScaleGUITrad(2)), at_left ? (SA_LEFT | SA_BOTTOM | SA_FORCE) : (SA_RIGHT | SA_BOTTOM | SA_FORCE));
}

/**
 * Draw a close box.
 * @param r      Rectangle of the box.`
 * @param colour Colour of the close box.
 */
static inline void DrawCloseBox(const Rect &r, Colours colour)
{
        if (colour != COLOUR_WHITE) DrawFrameRect(r.left, r.top, r.right, r.bottom, colour, FR_NONE);
        Point offset;
        Dimension d = GetSpriteSize(SPR_CLOSEBOX, &offset);
        d.width  -= offset.x;
        d.height -= offset.y;
        int s = ScaleSpriteTrad(1); /* Offset to account for shadow of SPR_CLOSEBOX */
        DrawSprite(SPR_CLOSEBOX, (colour != COLOUR_WHITE ? TC_BLACK : TC_SILVER) | (1U << PALETTE_TEXT_RECOLOUR), CenterBounds(r.left, r.right, d.width - s) - offset.x, CenterBounds(r.top, r.bottom, d.height - s) - offset.y);
}

/**
 * Draw a caption bar.
 * @param r           Rectangle of the bar.
 * @param colour      Colour of the window.
 * @param owner       'Owner' of the window.
 * @param text_colour Colour of the text.
 * @param str         Text to draw in the bar.
 * @param align       Alignment of the text.
 * @param fs          Font size of the text.
 */
void DrawCaption(const Rect &r, Colours colour, Owner owner, TextColour text_colour, StringID str, StringAlignment align, FontSize fs)
{
        bool company_owned = owner < MAX_COMPANIES;

        DrawFrameRect(r, colour, FR_BORDERONLY);
        Rect ir = r.Shrink(WidgetDimensions::scaled.bevel);
        DrawFrameRect(ir, colour, company_owned ? FR_LOWERED | FR_DARKENED | FR_BORDERONLY : FR_LOWERED | FR_DARKENED);

        if (company_owned) {
                GfxFillRect(ir.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(_company_colours[owner], SHADE_NORMAL));
        }

        if (str != STR_NULL) {
                Dimension d = GetStringBoundingBox(str);
                Point p = GetAlignedPosition(r, d, align);
                DrawString(r.left + WidgetDimensions::scaled.captiontext.left, r.right - WidgetDimensions::scaled.captiontext.left, p.y, str, text_colour, align, false, fs);
        }
}

/**
 * Draw a button with a dropdown (#WWT_DROPDOWN and #NWID_BUTTON_DROPDOWN).
 * @param r                Rectangle containing the widget.
 * @param colour           Background colour of the widget.
 * @param clicked_button   The button-part is clicked.
 * @param clicked_dropdown The drop-down part is clicked.
 * @param str              Text of the button.
 * @param align            Alignment of the text within the dropdown.
 *
 * @note Magic constants are also used in #NWidgetLeaf::ButtonHit.
 */
static inline void DrawButtonDropdown(const Rect &r, Colours colour, bool clicked_button, bool clicked_dropdown, StringID str, StringAlignment align)
{
        int dd_width  = NWidgetLeaf::dropdown_dimension.width;

        if (_current_text_dir == TD_LTR) {
                DrawFrameRect(r.left, r.top, r.right - dd_width, r.bottom, colour, clicked_button ? FR_LOWERED : FR_NONE);
                DrawImageButtons(r.WithWidth(dd_width, true), WWT_DROPDOWN, colour, clicked_dropdown, SPR_ARROW_DOWN, SA_CENTER);
                if (str != STR_NULL) {
                        DrawString(r.left + WidgetDimensions::scaled.dropdowntext.left, r.right - dd_width - WidgetDimensions::scaled.dropdowntext.right, CenterBounds(r.top, r.bottom, GetCharacterHeight(FS_NORMAL)), str, TC_BLACK, align);
                }
        } else {
                DrawFrameRect(r.left + dd_width, r.top, r.right, r.bottom, colour, clicked_button ? FR_LOWERED : FR_NONE);
                DrawImageButtons(r.WithWidth(dd_width, false), WWT_DROPDOWN, colour, clicked_dropdown, SPR_ARROW_DOWN, SA_CENTER);
                if (str != STR_NULL) {
                        DrawString(r.left + dd_width + WidgetDimensions::scaled.dropdowntext.left, r.right - WidgetDimensions::scaled.dropdowntext.right, CenterBounds(r.top, r.bottom, GetCharacterHeight(FS_NORMAL)), str, TC_BLACK, align);
                }
        }
}

/**
 * Paint all widgets of a window.
 */
void Window::DrawWidgets() const
{
        this->nested_root->Draw(this);

        if (this->flags & WF_WHITE_BORDER) {
                DrawFrameRect(0, 0, this->width - 1, this->height - 1, COLOUR_WHITE, FR_BORDERONLY);
        }

        if (this->flags & WF_HIGHLIGHTED) {
                extern bool _window_highlight_colour;
                for (const auto &pair : this->widget_lookup) {
                        const NWidgetBase *widget = pair.second;
                        if (!widget->IsHighlighted()) continue;

                        Rect outer = widget->GetCurrentRect();
                        Rect inner = outer.Shrink(WidgetDimensions::scaled.bevel).Expand(1);

                        int colour = _string_colourmap[_window_highlight_colour ? widget->GetHighlightColour() : TC_WHITE];

                        GfxFillRect(outer.left,     outer.top,    inner.left,      inner.bottom, colour);
                        GfxFillRect(inner.left + 1, outer.top,    inner.right - 1, inner.top,    colour);
                        GfxFillRect(inner.right,    outer.top,    outer.right,     inner.bottom, colour);
                        GfxFillRect(outer.left + 1, inner.bottom, outer.right - 1, outer.bottom, colour);
                }
        }
}

/**
 * Draw a sort button's up or down arrow symbol.
 * @param widget Sort button widget
 * @param state State of sort button
 */
void Window::DrawSortButtonState(WidgetID widget, SortButtonState state) const
{
        if (state == SBS_OFF) return;

        assert(!this->widget_lookup.empty());
        Rect r = this->GetWidget<NWidgetBase>(widget)->GetCurrentRect();

        /* Sort button uses the same sprites as vertical scrollbar */
        Dimension dim = NWidgetScrollbar::GetVerticalDimension();

        DrawSpriteIgnorePadding(state == SBS_DOWN ? SPR_ARROW_DOWN : SPR_ARROW_UP, PAL_NONE, r.WithWidth(dim.width, _current_text_dir == TD_LTR), SA_CENTER);
}

/**
 * Get width of up/down arrow of sort button state.
 * @return Width of space required by sort button arrow.
 */
int Window::SortButtonWidth()
{
        return NWidgetScrollbar::GetVerticalDimension().width + 1;
}

bool _draw_widget_outlines;

static void DrawOutline(const Window *, const NWidgetBase *wid)
{
        if (!_draw_widget_outlines || wid->current_x == 0 || wid->current_y == 0) return;

        DrawRectOutline(wid->GetCurrentRect(), PC_WHITE, 1, 4);
}

/**
 * @defgroup NestedWidgets Hierarchical widgets
 * Hierarchical widgets, also known as nested widgets, are widgets stored in a tree. At the leafs of the tree are (mostly) the 'real' widgets
 * visible to the user. At higher levels, widgets get organized in container widgets, until all widgets of the window are merged.
 *
 * \section nestedwidgetkinds Hierarchical widget kinds
 * A leaf widget is one of
 * <ul>
 * <li> #NWidgetLeaf for widgets visible for the user, or
 * <li> #NWidgetSpacer for creating (flexible) empty space between widgets.
 * </ul>
 * The purpose of a leaf widget is to provide interaction with the user by displaying settings, and/or allowing changing the settings.
 *
 * A container widget is one of
 * <ul>
 * <li> #NWidgetHorizontal for organizing child widgets in a (horizontal) row. The row switches order depending on the language setting (thus supporting
 *      right-to-left languages),
 * <li> #NWidgetHorizontalLTR for organizing child widgets in a (horizontal) row, always in the same order. All children below this container will also
 *      never swap order.
 * <li> #NWidgetVertical for organizing child widgets underneath each other.
 * <li> #NWidgetMatrix for organizing child widgets in a matrix form.
 * <li> #NWidgetBackground for adding a background behind its child widget.
 * <li> #NWidgetStacked for stacking child widgets on top of each other.
 * </ul>
 * The purpose of a container widget is to structure its leafs and sub-containers to allow proper resizing.
 *
 * \section nestedwidgetscomputations Hierarchical widget computations
 * The first 'computation' is the creation of the nested widgets tree by calling the constructors of the widgets listed above and calling \c Add() for every child,
 * or by means of specifying the tree as a collection of nested widgets parts and instantiating the tree from the array.
 *
 * After the creation step,
 * - The leafs have their own minimal size (\e min_x, \e min_y), filling (\e fill_x, \e fill_y), and resize steps (\e resize_x, \e resize_y).
 * - Containers only know what their children are, \e fill_x, \e fill_y, \e resize_x, and \e resize_y are not initialized.
 *
 * Computations in the nested widgets take place as follows:
 * <ol>
 * <li> A bottom-up sweep by recursively calling NWidgetBase::SetupSmallestSize() to initialize the smallest size (\e smallest_x, \e smallest_y) and
 *      to propagate filling and resize steps upwards to the root of the tree.
 * <li> A top-down sweep by recursively calling NWidgetBase::AssignSizePosition() with #ST_SMALLEST to make the smallest sizes consistent over
 *      the entire tree, and to assign the top-left (\e pos_x, \e pos_y) position of each widget in the tree. This step uses \e fill_x and \e fill_y at each
 *      node in the tree to decide how to fill each widget towards consistent sizes. Also the current size (\e current_x and \e current_y) is set.
 * <li> After initializing the smallest size in the widget tree with #ST_SMALLEST, the tree can be resized (the current size modified) by calling
 *      NWidgetBase::AssignSizePosition() at the root with #ST_RESIZE and the new size of the window. For proper functioning, the new size should be the smallest
 *      size + a whole number of resize steps in both directions (ie you can only resize in steps of length resize_{x,y} from smallest_{x,y}).
 * </ol>
 * After the second step, the current size of the widgets are set to the smallest size.
 *
 * To resize, perform the last step with the new window size. This can be done as often as desired.
 * When the smallest size of at least one widget changes, the whole procedure has to be redone from the start.
 *
 * @see NestedWidgetParts
 */

/**
 * Base class constructor.
 * @param tp Nested widget type.
 */
NWidgetBase::NWidgetBase(WidgetType tp) : ZeroedMemoryAllocator()
{
        this->type = tp;
}

/* ~NWidgetContainer() takes care of #next and #prev data members. */

/**
 * @fn void NWidgetBase::SetupSmallestSize(Window *w)
 * Compute smallest size needed by the widget.
 *
 * The smallest size of a widget is the smallest size that a widget needs to
 * display itself properly. In addition, filling and resizing of the widget are computed.
 * The function calls #Window::UpdateWidgetSize for each leaf widget and
 * background widget without child with a non-negative index.
 *
 * @param w          Window owning the widget.
 *
 * @note After the computation, the results can be queried by accessing the #smallest_x and #smallest_y data members of the widget.
 */

/**
 * @fn void NWidgetBase::AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool rtl)
 * Assign size and position to the widget.
 * @param sizing       Type of resizing to perform.
 * @param x            Horizontal offset of the widget relative to the left edge of the window.
 * @param y            Vertical offset of the widget relative to the top edge of the window.
 * @param given_width  Width allocated to the widget.
 * @param given_height Height allocated to the widget.
 * @param rtl          Adapt for right-to-left languages (position contents of horizontal containers backwards).
 *
 * Afterwards, \e pos_x and \e pos_y contain the top-left position of the widget, \e smallest_x and \e smallest_y contain
 * the smallest size such that all widgets of the window are consistent, and \e current_x and \e current_y contain the current size.
 */

/**
 * @fn void NWidgetBase::FillWidgetLookup(WidgetLookup &widget_lookup)
 * Fill the Window::widget_lookup with pointers to nested widgets in the tree.
 * @param widget_lookup The WidgetLookup.
 */

/**
 * @fn void NWidgetBase::Draw(const Window *w)
 * Draw the widgets of the tree.
 * The function calls #Window::DrawWidget for each widget with a non-negative index, after the widget itself is painted.
 * @param w Window that owns the tree.
 */

/**
 * Mark the widget as 'dirty' (in need of repaint).
 * @param w Window owning the widget.
 */
void NWidgetBase::SetDirty(const Window *w) const
{
        int abs_left = w->left + this->pos_x;
        int abs_top = w->top + this->pos_y;
        AddDirtyBlock(abs_left, abs_top, abs_left + this->current_x, abs_top + this->current_y);
}

/**
 * @fn NWidgetCore *NWidgetBase::GetWidgetFromPos(int x, int y)
 * Retrieve a widget by its position.
 * @param x Horizontal position relative to the left edge of the window.
 * @param y Vertical position relative to the top edge of the window.
 * @return Returns the deepest nested widget that covers the given position, or \c nullptr if no widget can be found.
 */

/**
 * Retrieve a widget by its type.
 * @param tp Widget type to search for.
 * @return Returns the first widget of the specified type, or \c nullptr if no widget can be found.
 */
NWidgetBase *NWidgetBase::GetWidgetOfType(WidgetType tp)
{
        return (this->type == tp) ? this : nullptr;
}

void NWidgetBase::ApplyAspectRatio()
{
        if (this->aspect_ratio == 0) return;
        if (this->smallest_x == 0 || this->smallest_y == 0) return;

        uint x = this->smallest_x;
        uint y = this->smallest_y;
        if (HasFlag(this->aspect_flags, AspectFlags::ResizeX)) x = std::max(this->smallest_x, static_cast<uint>(this->smallest_y * std::abs(this->aspect_ratio)));
        if (HasFlag(this->aspect_flags, AspectFlags::ResizeY)) y = std::max(this->smallest_y, static_cast<uint>(this->smallest_x / std::abs(this->aspect_ratio)));

        this->smallest_x = x;
        this->smallest_y = y;
}

void NWidgetBase::AdjustPaddingForZoom()
{
        this->padding = ScaleGUITrad(this->uz_padding);
}

/**
 * Constructor for resizable nested widgets.
 * @param tp     Nested widget type.
 * @param fill_x Horizontal fill step size, \c 0 means no filling is allowed.
 * @param fill_y Vertical fill step size, \c 0 means no filling is allowed.
 */
NWidgetResizeBase::NWidgetResizeBase(WidgetType tp, uint fill_x, uint fill_y) : NWidgetBase(tp)
{
        this->fill_x = fill_x;
        this->fill_y = fill_y;
}

/**
 * Set desired aspect ratio of this widget.
 * @param ratio Desired aspect ratio, or 0 for none.
 * @param flags Dimensions which should be resized.
 */
void NWidgetResizeBase::SetAspect(float ratio, AspectFlags flags)
{
        this->aspect_ratio = ratio;
        this->aspect_flags = flags;
}

/**
 * Set desired aspect ratio of this widget, in terms of horizontal and vertical dimensions.
 * @param x_ratio Desired horizontal component of aspect ratio.
 * @param y_ratio Desired vertical component of aspect ratio.
 * @param flags Dimensions which should be resized.
 */
void NWidgetResizeBase::SetAspect(int x_ratio, int y_ratio, AspectFlags flags)
{
        this->SetAspect(static_cast<float>(x_ratio) / static_cast<float>(y_ratio), flags);
}

void NWidgetResizeBase::AdjustPaddingForZoom()
{
        if (!this->absolute) {
                this->min_x = ScaleGUITrad(this->uz_min_x);
                this->min_y = std::max(ScaleGUITrad(this->uz_min_y), this->uz_text_lines * GetCharacterHeight(this->uz_text_size) + ScaleGUITrad(this->uz_text_spacing));
        }
        NWidgetBase::AdjustPaddingForZoom();
}

/**
 * Set minimal size of the widget.
 * @param min_x Horizontal minimal size of the widget.
 * @param min_y Vertical minimal size of the widget.
 */
void NWidgetResizeBase::SetMinimalSize(uint min_x, uint min_y)
{
        this->uz_min_x = std::max(this->uz_min_x, min_x);
        this->uz_min_y = std::max(this->uz_min_y, min_y);
        this->min_x = ScaleGUITrad(this->uz_min_x);
        this->min_y = std::max(ScaleGUITrad(this->uz_min_y), this->uz_text_lines * GetCharacterHeight(this->uz_text_size) + ScaleGUITrad(this->uz_text_spacing));
}

/**
 * Set absolute (post-scaling) minimal size of the widget.
 * @param min_x Horizontal minimal size of the widget.
 * @param min_y Vertical minimal size of the widget.
 */
void NWidgetResizeBase::SetMinimalSizeAbsolute(uint min_x, uint min_y)
{
        this->absolute = true;
        this->min_x = std::max(this->min_x, min_x);
        this->min_y = std::max(this->min_y, min_y);
}

/**
 * Set minimal text lines for the widget.
 * @param min_lines Number of text lines of the widget.
 * @param spacing   Extra unscaled spacing (eg WidgetDimensions::unscaled.framerect.Vertical()) of the widget.
 * @param size      Font size of text.
 */
void NWidgetResizeBase::SetMinimalTextLines(uint8_t min_lines, uint8_t spacing, FontSize size)
{
        this->uz_text_lines = min_lines;
        this->uz_text_spacing = spacing;
        this->uz_text_size = size;
        this->min_y = std::max(ScaleGUITrad(this->uz_min_y), this->uz_text_lines * GetCharacterHeight(this->uz_text_size) + ScaleGUITrad(this->uz_text_spacing));
}

/**
 * Set the filling of the widget from initial size.
 * @param fill_x Horizontal fill step size, \c 0 means no filling is allowed.
 * @param fill_y Vertical fill step size, \c 0 means no filling is allowed.
 */
void NWidgetResizeBase::SetFill(uint fill_x, uint fill_y)
{
        this->fill_x = fill_x;
        this->fill_y = fill_y;
}

/**
 * Set resize step of the widget.
 * @param resize_x Resize step in horizontal direction, value \c 0 means no resize, otherwise the step size in pixels.
 * @param resize_y Resize step in vertical direction, value \c 0 means no resize, otherwise the step size in pixels.
 */
void NWidgetResizeBase::SetResize(uint resize_x, uint resize_y)
{
        this->resize_x = resize_x;
        this->resize_y = resize_y;
}

/**
 * Try to set optimum widget size for a multiline text widget.
 * The window will need to be reinited if the size is changed.
 * @param str Multiline string contents that will fill the widget.
 * @param max_line Maximum number of lines.
 * @return true iff the widget minimum size has changed.
 */
bool NWidgetResizeBase::UpdateMultilineWidgetSize(const std::string &str, int max_lines)
{
        int y = GetStringHeight(str, this->current_x);
        if (y > max_lines * GetCharacterHeight(FS_NORMAL)) {
                /* Text at the current width is too tall, so try to guess a better width. */
                Dimension d = GetStringBoundingBox(str);
                d.height *= max_lines;
                d.width /= 2;
                return this->UpdateSize(d.width, d.height);
        }
        return this->UpdateVerticalSize(y);
}

/**
 * Set absolute (post-scaling) minimal size of the widget.
 * The window will need to be reinited if the size is changed.
 * @param min_x Horizontal minimal size of the widget.
 * @param min_y Vertical minimal size of the widget.
 * @return true iff the widget minimum size has changed.
 */
bool NWidgetResizeBase::UpdateSize(uint min_x, uint min_y)
{
        if (min_x == this->min_x && min_y == this->min_y) return false;
        this->min_x = min_x;
        this->min_y = min_y;
        return true;
}

/**
 * Set absolute (post-scaling) minimal size of the widget.
 * The window will need to be reinited if the size is changed.
 * @param min_y Vertical minimal size of the widget.
 * @return true iff the widget minimum size has changed.
 */
bool NWidgetResizeBase::UpdateVerticalSize(uint min_y)
{
        if (min_y == this->min_y) return false;
        this->min_y = min_y;
        return true;
}

void NWidgetResizeBase::AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool)
{
        this->StoreSizePosition(sizing, x, y, given_width, given_height);
}

/**
 * Initialization of a 'real' widget.
 * @param tp          Type of the widget.
 * @param colour      Colour of the widget.
 * @param index       Index of the widget.
 * @param fill_x      Default horizontal filling.
 * @param fill_y      Default vertical filling.
 * @param widget_data Data component of the widget. @see Widget::data
 * @param tool_tip    Tool tip of the widget. @see Widget::tooltips
 */
NWidgetCore::NWidgetCore(WidgetType tp, Colours colour, WidgetID index, uint fill_x, uint fill_y, uint32_t widget_data, StringID tool_tip) : NWidgetResizeBase(tp, fill_x, fill_y), index(index)
{
        this->colour = colour;
        this->widget_data = widget_data;
        this->tool_tip = tool_tip;
        this->scrollbar_index = -1;
        this->text_colour = tp == WWT_CAPTION ? TC_WHITE : TC_BLACK;
        this->text_size = FS_NORMAL;
        this->align = SA_CENTER;
}

/**
 * Set data and tool tip of the nested widget.
 * @param widget_data Data to use.
 * @param tool_tip    Tool tip string to use.
 */
void NWidgetCore::SetDataTip(uint32_t widget_data, StringID tool_tip)
{
        this->widget_data = widget_data;
        this->tool_tip = tool_tip;
}

/**
 * Set the text style of the nested widget.
 * @param colour TextColour to use.
 * @param size Font size to use.
 */
void NWidgetCore::SetTextStyle(TextColour colour, FontSize size)
{
        this->text_colour = colour;
        this->text_size = size;
}

/**
 * Set the tool tip of the nested widget.
 * @param tool_tip Tool tip string to use.
 */
void NWidgetCore::SetToolTip(StringID tool_tip)
{
        this->tool_tip = tool_tip;
}

/**
 * Set the text/image alignment of the nested widget.
 * @param align Alignment to use.
 */
void NWidgetCore::SetAlignment(StringAlignment align)
{
        this->align = align;
}

void NWidgetCore::FillWidgetLookup(WidgetLookup &widget_lookup)
{
        if (this->index >= 0) widget_lookup[this->index] = this;
}

NWidgetCore *NWidgetCore::GetWidgetFromPos(int x, int y)
{
        return (IsInsideBS(x, this->pos_x, this->current_x) && IsInsideBS(y, this->pos_y, this->current_y)) ? this : nullptr;
}

NWidgetBase *NWidgetContainer::GetWidgetOfType(WidgetType tp)
{
        if (this->type == tp) return this;
        for (const auto &child_wid : this->children) {
                NWidgetBase *nwid = child_wid->GetWidgetOfType(tp);
                if (nwid != nullptr) return nwid;
        }
        return nullptr;
}

void NWidgetContainer::AdjustPaddingForZoom()
{
        for (const auto &child_wid : this->children) {
                child_wid->AdjustPaddingForZoom();
        }
        NWidgetBase::AdjustPaddingForZoom();
}

/**
 * Append widget \a wid to container.
 * @param wid Widget to append.
 */
void NWidgetContainer::Add(std::unique_ptr<NWidgetBase> &&wid)
{
        assert(wid != nullptr);
        wid->parent = this;
        this->children.push_back(std::move(wid));
}

void NWidgetContainer::FillWidgetLookup(WidgetLookup &widget_lookup)
{
        for (const auto &child_wid : this->children) {
                child_wid->FillWidgetLookup(widget_lookup);
        }
}

void NWidgetContainer::Draw(const Window *w)
{
        for (const auto &child_wid : this->children) {
                child_wid->Draw(w);
        }

        DrawOutline(w, this);
}

NWidgetCore *NWidgetContainer::GetWidgetFromPos(int x, int y)
{
        if (!IsInsideBS(x, this->pos_x, this->current_x) || !IsInsideBS(y, this->pos_y, this->current_y)) return nullptr;

        for (const auto &child_wid : this->children) {
                NWidgetCore *nwid = child_wid->GetWidgetFromPos(x, y);
                if (nwid != nullptr) return nwid;
        }
        return nullptr;
}

/**
 * Widgets stacked on top of each other.
 */
NWidgetStacked::NWidgetStacked(WidgetID index) : NWidgetContainer(NWID_SELECTION), index(index)
{
}

void NWidgetStacked::SetupSmallestSize(Window *w)
{
        /* Zero size plane selected */
        if (this->shown_plane >= SZSP_BEGIN) {
                Dimension size    = {0, 0};
                Dimension padding = {0, 0};
                Dimension fill    = {(this->shown_plane == SZSP_HORIZONTAL), (this->shown_plane == SZSP_VERTICAL)};
                Dimension resize  = {(this->shown_plane == SZSP_HORIZONTAL), (this->shown_plane == SZSP_VERTICAL)};
                /* Here we're primarily interested in the value of resize */
                if (this->index >= 0) w->UpdateWidgetSize(this->index, size, padding, fill, resize);

                this->smallest_x = size.width;
                this->smallest_y = size.height;
                this->fill_x = fill.width;
                this->fill_y = fill.height;
                this->resize_x = resize.width;
                this->resize_y = resize.height;
                this->ApplyAspectRatio();
                return;
        }

        /* First sweep, recurse down and compute minimal size and filling. */
        this->smallest_x = 0;
        this->smallest_y = 0;
        this->fill_x = this->IsEmpty() ? 0 : 1;
        this->fill_y = this->IsEmpty() ? 0 : 1;
        this->resize_x = this->IsEmpty() ? 0 : 1;
        this->resize_y = this->IsEmpty() ? 0 : 1;
        for (const auto &child_wid : this->children) {
                child_wid->SetupSmallestSize(w);

                this->smallest_x = std::max(this->smallest_x, child_wid->smallest_x + child_wid->padding.Horizontal());
                this->smallest_y = std::max(this->smallest_y, child_wid->smallest_y + child_wid->padding.Vertical());
                this->fill_x = std::lcm(this->fill_x, child_wid->fill_x);
                this->fill_y = std::lcm(this->fill_y, child_wid->fill_y);
                this->resize_x = std::lcm(this->resize_x, child_wid->resize_x);
                this->resize_y = std::lcm(this->resize_y, child_wid->resize_y);
                this->ApplyAspectRatio();
        }
}

void NWidgetStacked::AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool rtl)
{
        assert(given_width >= this->smallest_x && given_height >= this->smallest_y);
        this->StoreSizePosition(sizing, x, y, given_width, given_height);

        if (this->shown_plane >= SZSP_BEGIN) return;

        for (const auto &child_wid : this->children) {
                uint hor_step = (sizing == ST_SMALLEST) ? 1 : child_wid->GetHorizontalStepSize(sizing);
                uint child_width = ComputeMaxSize(child_wid->smallest_x, given_width - child_wid->padding.Horizontal(), hor_step);
                uint child_pos_x = (rtl ? child_wid->padding.right : child_wid->padding.left);

                uint vert_step = (sizing == ST_SMALLEST) ? 1 : child_wid->GetVerticalStepSize(sizing);
                uint child_height = ComputeMaxSize(child_wid->smallest_y, given_height - child_wid->padding.Vertical(), vert_step);
                uint child_pos_y = child_wid->padding.top;

                child_wid->AssignSizePosition(sizing, x + child_pos_x, y + child_pos_y, child_width, child_height, rtl);
        }
}

void NWidgetStacked::FillWidgetLookup(WidgetLookup &widget_lookup)
{
        /* We need to update widget_lookup later. */
        this->widget_lookup = &widget_lookup;

        if (this->index >= 0) widget_lookup[this->index] = this;
        NWidgetContainer::FillWidgetLookup(widget_lookup);
        /* In case widget IDs are repeated, make sure Window::GetWidget works on displayed widgets. */
        if (static_cast<size_t>(this->shown_plane) < this->children.size()) this->children[shown_plane]->FillWidgetLookup(widget_lookup);
}

void NWidgetStacked::Draw(const Window *w)
{
        if (this->shown_plane >= SZSP_BEGIN) return;

        assert(static_cast<size_t>(this->shown_plane) < this->children.size());
        this->children[shown_plane]->Draw(w);
        DrawOutline(w, this);
}

NWidgetCore *NWidgetStacked::GetWidgetFromPos(int x, int y)
{
        if (this->shown_plane >= SZSP_BEGIN) return nullptr;

        if (!IsInsideBS(x, this->pos_x, this->current_x) || !IsInsideBS(y, this->pos_y, this->current_y)) return nullptr;

        if (static_cast<size_t>(this->shown_plane) >= this->children.size()) return nullptr;
        return this->children[shown_plane]->GetWidgetFromPos(x, y);
}

/**
 * Select which plane to show (for #NWID_SELECTION only).
 * @param plane Plane number to display.
 * @return true iff the shown plane changed.
 */
bool NWidgetStacked::SetDisplayedPlane(int plane)
{
        if (this->shown_plane == plane) return false;
        this->shown_plane = plane;
        /* In case widget IDs are repeated, make sure Window::GetWidget works on displayed widgets. */
        if (static_cast<size_t>(this->shown_plane) < this->children.size()) this->children[shown_plane]->FillWidgetLookup(*this->widget_lookup);
        return true;
}

class NWidgetLayer : public NWidgetContainer {
public:
        NWidgetLayer(WidgetID index);

        void SetupSmallestSize(Window *w) override;
        void AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool rtl) override;

        void Draw(const Window *w) override;

        const WidgetID index; ///< If non-negative, index in the #Window::widget_lookup.
};

NWidgetLayer::NWidgetLayer(WidgetID index) : NWidgetContainer(NWID_LAYER), index(index) {}

void NWidgetLayer::SetupSmallestSize(Window *w)
{
        /* First sweep, recurse down and compute minimal size and filling. */
        this->smallest_x = 0;
        this->smallest_y = 0;
        this->fill_x = this->IsEmpty() ? 0 : 1;
        this->fill_y = this->IsEmpty() ? 0 : 1;
        this->resize_x = this->IsEmpty() ? 0 : 1;
        this->resize_y = this->IsEmpty() ? 0 : 1;
        for (const auto &child_wid : this->children) {
                child_wid->SetupSmallestSize(w);

                this->smallest_x = std::max(this->smallest_x, child_wid->smallest_x + child_wid->padding.Horizontal());
                this->smallest_y = std::max(this->smallest_y, child_wid->smallest_y + child_wid->padding.Vertical());
                this->fill_x = std::lcm(this->fill_x, child_wid->fill_x);
                this->fill_y = std::lcm(this->fill_y, child_wid->fill_y);
                this->resize_x = std::lcm(this->resize_x, child_wid->resize_x);
                this->resize_y = std::lcm(this->resize_y, child_wid->resize_y);
                this->ApplyAspectRatio();
        }
}

void NWidgetLayer::AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool rtl)
{
        assert(given_width >= this->smallest_x && given_height >= this->smallest_y);
        this->StoreSizePosition(sizing, x, y, given_width, given_height);

        for (const auto &child_wid : this->children) {
                uint hor_step = (sizing == ST_SMALLEST) ? 1 : child_wid->GetHorizontalStepSize(sizing);
                uint child_width = ComputeMaxSize(child_wid->smallest_x, given_width - child_wid->padding.Horizontal(), hor_step);
                uint child_pos_x = (rtl ? child_wid->padding.right : child_wid->padding.left);

                uint vert_step = (sizing == ST_SMALLEST) ? 1 : child_wid->GetVerticalStepSize(sizing);
                uint child_height = ComputeMaxSize(child_wid->smallest_y, given_height - child_wid->padding.Vertical(), vert_step);
                uint child_pos_y = child_wid->padding.top;

                child_wid->AssignSizePosition(sizing, x + child_pos_x, y + child_pos_y, child_width, child_height, rtl);
        }
}

void NWidgetLayer::Draw(const Window *w)
{
        /* Draw in reverse order, as layers are arranged top-down. */
        for (auto it = std::rbegin(this->children); it != std::rend(this->children); ++it) {
                (*it)->Draw(w);
        }

        DrawOutline(w, this);
}

NWidgetPIPContainer::NWidgetPIPContainer(WidgetType tp, NWidContainerFlags flags) : NWidgetContainer(tp)
{
        this->flags = flags;
}

void NWidgetPIPContainer::AdjustPaddingForZoom()
{
        this->pip_pre = ScaleGUITrad(this->uz_pip_pre);
        this->pip_inter = ScaleGUITrad(this->uz_pip_inter);
        this->pip_post = ScaleGUITrad(this->uz_pip_post);
        NWidgetContainer::AdjustPaddingForZoom();
}

/**
 * Set additional pre/inter/post space for the container.
 *
 * @param pip_pre   Additional space in front of the first child widget (above
 *                  for the vertical container, at the left for the horizontal container).
 * @param pip_inter Additional space between two child widgets.
 * @param pip_post  Additional space after the last child widget (below for the
 *                  vertical container, at the right for the horizontal container).
 */
void NWidgetPIPContainer::SetPIP(uint8_t pip_pre, uint8_t pip_inter, uint8_t pip_post)
{
        this->uz_pip_pre = pip_pre;
        this->uz_pip_inter = pip_inter;
        this->uz_pip_post = pip_post;

        this->pip_pre = ScaleGUITrad(this->uz_pip_pre);
        this->pip_inter = ScaleGUITrad(this->uz_pip_inter);
        this->pip_post = ScaleGUITrad(this->uz_pip_post);
}

/**
 * Set additional pre/inter/post space for the container.
 *
 * @param pip_ratio_pre   Ratio of additional space in front of the first child widget (above
 *                        for the vertical container, at the left for the horizontal container).
 * @param pip_ratio_inter Ratio of additional space between two child widgets.
 * @param pip_ratio_post  Ratio of additional space after the last child widget (below for the
 *                        vertical container, at the right for the horizontal container).
 */
void NWidgetPIPContainer::SetPIPRatio(uint8_t pip_ratio_pre, uint8_t pip_ratio_inter, uint8_t pip_ratio_post)
{
        this->pip_ratio_pre = pip_ratio_pre;
        this->pip_ratio_inter = pip_ratio_inter;
        this->pip_ratio_post = pip_ratio_post;
}

/** Horizontal container widget. */
NWidgetHorizontal::NWidgetHorizontal(NWidContainerFlags flags) : NWidgetPIPContainer(NWID_HORIZONTAL, flags)
{
}

void NWidgetHorizontal::SetupSmallestSize(Window *w)
{
        this->smallest_x = 0; // Sum of minimal size of all children.
        this->smallest_y = 0; // Biggest child.
        this->fill_x = 0;     // smallest non-zero child widget fill step.
        this->fill_y = 1;     // smallest common child fill step.
        this->resize_x = 0;   // smallest non-zero child widget resize step.
        this->resize_y = 1;   // smallest common child resize step.
        this->gaps = 0;

        /* 1a. Forward call, collect longest/widest child length. */
        uint longest = 0; // Longest child found.
        uint max_vert_fill = 0; // Biggest vertical fill step.
        for (const auto &child_wid : this->children) {
                child_wid->SetupSmallestSize(w);
                longest = std::max(longest, child_wid->smallest_x);
                max_vert_fill = std::max(max_vert_fill, child_wid->GetVerticalStepSize(ST_SMALLEST));
                this->smallest_y = std::max(this->smallest_y, child_wid->smallest_y + child_wid->padding.Vertical());
                if (child_wid->smallest_x != 0 || child_wid->fill_x != 0) this->gaps++;
        }
        if (this->gaps > 0) this->gaps--; // Number of gaps is number of widgets less one.
        /* 1b. Make the container higher if needed to accommodate all children nicely. */
        [[maybe_unused]] uint max_smallest = this->smallest_y + 3 * max_vert_fill; // Upper limit to computing smallest height.
        uint cur_height = this->smallest_y;
        for (;;) {
                for (const auto &child_wid : this->children) {
                        uint step_size = child_wid->GetVerticalStepSize(ST_SMALLEST);
                        uint child_height = child_wid->smallest_y + child_wid->padding.Vertical();
                        if (step_size > 1 && child_height < cur_height) { // Small step sizes or already fitting children are not interesting.
                                uint remainder = (cur_height - child_height) % step_size;
                                if (remainder > 0) { // Child did not fit entirely, widen the container.
                                        cur_height += step_size - remainder;
                                        assert(cur_height < max_smallest); // Safeguard against infinite height expansion.
                                        /* Remaining children will adapt to the new cur_height, thus speeding up the computation. */
                                }
                        }
                }
                if (this->smallest_y == cur_height) break;
                this->smallest_y = cur_height; // Smallest height got changed, try again.
        }
        /* 2. For containers that must maintain equal width, extend child minimal size. */
        for (const auto &child_wid : this->children) {
                child_wid->smallest_y = this->smallest_y - child_wid->padding.Vertical();
                child_wid->ApplyAspectRatio();
                longest = std::max(longest, child_wid->smallest_x);
        }
        if (this->flags & NC_EQUALSIZE) {
                for (const auto &child_wid : this->children) {
                        if (child_wid->fill_x == 1) child_wid->smallest_x = longest;
                }
        }
        /* 3. Compute smallest, fill, and resize values of the container. */
        for (const auto &child_wid : this->children) {
                this->smallest_x += child_wid->smallest_x + child_wid->padding.Horizontal();
                if (child_wid->fill_x > 0) {
                        if (this->fill_x == 0 || this->fill_x > child_wid->fill_x) this->fill_x = child_wid->fill_x;
                }
                this->fill_y = std::lcm(this->fill_y, child_wid->fill_y);

                if (child_wid->resize_x > 0) {
                        if (this->resize_x == 0 || this->resize_x > child_wid->resize_x) this->resize_x = child_wid->resize_x;
                }
                this->resize_y = std::lcm(this->resize_y, child_wid->resize_y);
        }
        if (this->fill_x == 0 && this->pip_ratio_pre + this->pip_ratio_inter + this->pip_ratio_post > 0) this->fill_x = 1;
        /* 4. Increase by required PIP space. */
        this->smallest_x += this->pip_pre + this->gaps * this->pip_inter + this->pip_post;
}

void NWidgetHorizontal::AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool rtl)
{
        assert(given_width >= this->smallest_x && given_height >= this->smallest_y);

        /* Compute additional width given to us. */
        uint additional_length = given_width - (this->pip_pre + this->gaps * this->pip_inter + this->pip_post);
        for (const auto &child_wid : this->children) {
                if (child_wid->smallest_x != 0 || child_wid->fill_x != 0) additional_length -= child_wid->smallest_x + child_wid->padding.Horizontal();
        }

        this->StoreSizePosition(sizing, x, y, given_width, given_height);

        /* In principle, the additional horizontal space is distributed evenly over the available resizable children. Due to step sizes, this may not always be feasible.
         * To make resizing work as good as possible, first children with biggest step sizes are done. These may get less due to rounding down.
         * This additional space is then given to children with smaller step sizes. This will give a good result when resize steps of each child is a multiple
         * of the child with the smallest non-zero stepsize.
         *
         * Since child sizes are computed out of order, positions cannot be calculated until all sizes are known. That means it is not possible to compute the child
         * size and position, and directly call child->AssignSizePosition() with the computed values.
         * Instead, computed child widths and heights are stored in child->current_x and child->current_y values. That is allowed, since this method overwrites those values
         * then we call the child.
         */

        /* First loop: Find biggest stepsize, find number of children that want a piece of the pie, handle vertical size for all children,
         * handle horizontal size for non-resizing children.
         */
        int num_changing_childs = 0; // Number of children that can change size.
        uint biggest_stepsize = 0;
        for (const auto &child_wid : this->children) {
                uint hor_step = child_wid->GetHorizontalStepSize(sizing);
                if (hor_step > 0) {
                        if (!(flags & NC_BIGFIRST)) num_changing_childs++;
                        biggest_stepsize = std::max(biggest_stepsize, hor_step);
                } else {
                        child_wid->current_x = child_wid->smallest_x;
                }

                uint vert_step = (sizing == ST_SMALLEST) ? 1 : child_wid->GetVerticalStepSize(sizing);
                child_wid->current_y = ComputeMaxSize(child_wid->smallest_y, given_height - child_wid->padding.Vertical(), vert_step);
        }

        /* First.5 loop: count how many children are of the biggest step size. */
        if ((flags & NC_BIGFIRST) && biggest_stepsize > 0) {
                for (const auto &child_wid : this->children) {
                        uint hor_step = child_wid->GetHorizontalStepSize(sizing);
                        if (hor_step == biggest_stepsize) {
                                num_changing_childs++;
                        }
                }
        }

        /* Second loop: Allocate the additional horizontal space over the resizing children, starting with the biggest resize steps. */
        while (biggest_stepsize > 0) {
                uint next_biggest_stepsize = 0;
                for (const auto &child_wid : this->children) {
                        uint hor_step = child_wid->GetHorizontalStepSize(sizing);
                        if (hor_step > biggest_stepsize) continue; // Already done
                        if (hor_step == biggest_stepsize) {
                                uint increment = additional_length / num_changing_childs;
                                num_changing_childs--;
                                if (hor_step > 1) increment -= increment % hor_step;
                                child_wid->current_x = child_wid->smallest_x + increment;
                                additional_length -= increment;
                                continue;
                        }
                        next_biggest_stepsize = std::max(next_biggest_stepsize, hor_step);
                }
                biggest_stepsize = next_biggest_stepsize;

                if (num_changing_childs == 0 && (flags & NC_BIGFIRST) && biggest_stepsize > 0) {
                        /* Second.5 loop: count how many children are of the updated biggest step size. */
                        for (const auto &child_wid : this->children) {
                                uint hor_step = child_wid->GetHorizontalStepSize(sizing);
                                if (hor_step == biggest_stepsize) {
                                        num_changing_childs++;
                                }
                        }
                }
        }
        assert(num_changing_childs == 0);

        uint pre = this->pip_pre;
        uint inter = this->pip_inter;

        if (additional_length > 0) {
                /* Allocate remaining space by pip ratios. If this doesn't round exactly, the unused space will fall into pip_post
                 * which is never explicitly needed. */
                int r = this->pip_ratio_pre + this->gaps * this->pip_ratio_inter + this->pip_ratio_post;
                if (r > 0) {
                        pre += this->pip_ratio_pre * additional_length / r;
                        if (this->gaps > 0) inter += this->pip_ratio_inter * additional_length / r;
                }
        }

        /* Third loop: Compute position and call the child. */
        uint position = rtl ? this->current_x - pre : pre; // Place to put next child relative to origin of the container.
        for (const auto &child_wid : this->children) {
                uint child_width = child_wid->current_x;
                uint child_x = x + (rtl ? position - child_width - child_wid->padding.left : position + child_wid->padding.left);
                uint child_y = y + child_wid->padding.top;

                child_wid->AssignSizePosition(sizing, child_x, child_y, child_width, child_wid->current_y, rtl);
                if (child_wid->current_x != 0) {
                        uint padded_child_width = child_width + child_wid->padding.Horizontal() + inter;
                        position = rtl ? position - padded_child_width : position + padded_child_width;
                }
        }
}

/** Horizontal left-to-right container widget. */
NWidgetHorizontalLTR::NWidgetHorizontalLTR(NWidContainerFlags flags) : NWidgetHorizontal(flags)
{
        this->type = NWID_HORIZONTAL_LTR;
}

void NWidgetHorizontalLTR::AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool)
{
        NWidgetHorizontal::AssignSizePosition(sizing, x, y, given_width, given_height, false);
}

/** Vertical container widget. */
NWidgetVertical::NWidgetVertical(NWidContainerFlags flags) : NWidgetPIPContainer(NWID_VERTICAL, flags)
{
}

void NWidgetVertical::SetupSmallestSize(Window *w)
{
        this->smallest_x = 0; // Biggest child.
        this->smallest_y = 0; // Sum of minimal size of all children.
        this->fill_x = 1;     // smallest common child fill step.
        this->fill_y = 0;     // smallest non-zero child widget fill step.
        this->resize_x = 1;   // smallest common child resize step.
        this->resize_y = 0;   // smallest non-zero child widget resize step.
        this->gaps = 0;

        /* 1a. Forward call, collect longest/widest child length. */
        uint highest = 0; // Highest child found.
        uint max_hor_fill = 0; // Biggest horizontal fill step.
        for (const auto &child_wid : this->children) {
                child_wid->SetupSmallestSize(w);
                highest = std::max(highest, child_wid->smallest_y);
                max_hor_fill = std::max(max_hor_fill, child_wid->GetHorizontalStepSize(ST_SMALLEST));
                this->smallest_x = std::max(this->smallest_x, child_wid->smallest_x + child_wid->padding.Horizontal());
                if (child_wid->smallest_y != 0 || child_wid->fill_y != 0) this->gaps++;
        }
        if (this->gaps > 0) this->gaps--; // Number of gaps is number of widgets less one.
        /* 1b. Make the container wider if needed to accommodate all children nicely. */
        [[maybe_unused]] uint max_smallest = this->smallest_x + 3 * max_hor_fill; // Upper limit to computing smallest height.
        uint cur_width = this->smallest_x;
        for (;;) {
                for (const auto &child_wid : this->children) {
                        uint step_size = child_wid->GetHorizontalStepSize(ST_SMALLEST);
                        uint child_width = child_wid->smallest_x + child_wid->padding.Horizontal();
                        if (step_size > 1 && child_width < cur_width) { // Small step sizes or already fitting children are not interesting.
                                uint remainder = (cur_width - child_width) % step_size;
                                if (remainder > 0) { // Child did not fit entirely, widen the container.
                                        cur_width += step_size - remainder;
                                        assert(cur_width < max_smallest); // Safeguard against infinite width expansion.
                                        /* Remaining children will adapt to the new cur_width, thus speeding up the computation. */
                                }
                        }
                }
                if (this->smallest_x == cur_width) break;
                this->smallest_x = cur_width; // Smallest width got changed, try again.
        }
        /* 2. For containers that must maintain equal width, extend children minimal size. */
        for (const auto &child_wid : this->children) {
                child_wid->smallest_x = this->smallest_x - child_wid->padding.Horizontal();
                child_wid->ApplyAspectRatio();
                highest = std::max(highest, child_wid->smallest_y);
        }
        if (this->flags & NC_EQUALSIZE) {
                for (const auto &child_wid : this->children) {
                        if (child_wid->fill_y == 1) child_wid->smallest_y = highest;
                }
        }
        /* 3. Compute smallest, fill, and resize values of the container. */
        for (const auto &child_wid : this->children) {
                this->smallest_y += child_wid->smallest_y + child_wid->padding.Vertical();
                if (child_wid->fill_y > 0) {
                        if (this->fill_y == 0 || this->fill_y > child_wid->fill_y) this->fill_y = child_wid->fill_y;
                }
                this->fill_x = std::lcm(this->fill_x, child_wid->fill_x);

                if (child_wid->resize_y > 0) {
                        if (this->resize_y == 0 || this->resize_y > child_wid->resize_y) this->resize_y = child_wid->resize_y;
                }
                this->resize_x = std::lcm(this->resize_x, child_wid->resize_x);
        }
        if (this->fill_y == 0 && this->pip_ratio_pre + this->pip_ratio_inter + this->pip_ratio_post > 0) this->fill_y = 1;
        /* 4. Increase by required PIP space. */
        this->smallest_y += this->pip_pre + this->gaps * this->pip_inter + this->pip_post;
}

void NWidgetVertical::AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool rtl)
{
        assert(given_width >= this->smallest_x && given_height >= this->smallest_y);

        /* Compute additional height given to us. */
        uint additional_length = given_height - (this->pip_pre + this->gaps * this->pip_inter + this->pip_post);
        for (const auto &child_wid : this->children) {
                if (child_wid->smallest_y != 0 || child_wid->fill_y != 0) additional_length -= child_wid->smallest_y + child_wid->padding.Vertical();
        }

        this->StoreSizePosition(sizing, x, y, given_width, given_height);

        /* Like the horizontal container, the vertical container also distributes additional height evenly, starting with the children with the biggest resize steps.
         * It also stores computed widths and heights into current_x and current_y values of the child.
         */

        /* First loop: Find biggest stepsize, find number of children that want a piece of the pie, handle horizontal size for all children, handle vertical size for non-resizing child. */
        int num_changing_childs = 0; // Number of children that can change size.
        uint biggest_stepsize = 0;
        for (const auto &child_wid : this->children) {
                uint vert_step = child_wid->GetVerticalStepSize(sizing);
                if (vert_step > 0) {
                        if (!(flags & NC_BIGFIRST)) num_changing_childs++;
                        biggest_stepsize = std::max(biggest_stepsize, vert_step);
                } else {
                        child_wid->current_y = child_wid->smallest_y;
                }

                uint hor_step = (sizing == ST_SMALLEST) ? 1 : child_wid->GetHorizontalStepSize(sizing);
                child_wid->current_x = ComputeMaxSize(child_wid->smallest_x, given_width - child_wid->padding.Horizontal(), hor_step);
        }

        /* First.5 loop: count how many children are of the biggest step size. */
        if ((this->flags & NC_BIGFIRST) && biggest_stepsize > 0) {
                for (const auto &child_wid : this->children) {
                        uint vert_step = child_wid->GetVerticalStepSize(sizing);
                        if (vert_step == biggest_stepsize) {
                                num_changing_childs++;
                        }
                }
        }

        /* Second loop: Allocate the additional vertical space over the resizing children, starting with the biggest resize steps. */
        while (biggest_stepsize > 0) {
                uint next_biggest_stepsize = 0;
                for (const auto &child_wid : this->children) {
                        uint vert_step = child_wid->GetVerticalStepSize(sizing);
                        if (vert_step > biggest_stepsize) continue; // Already done
                        if (vert_step == biggest_stepsize) {
                                uint increment = additional_length / num_changing_childs;
                                num_changing_childs--;
                                if (vert_step > 1) increment -= increment % vert_step;
                                child_wid->current_y = child_wid->smallest_y + increment;
                                additional_length -= increment;
                                continue;
                        }
                        next_biggest_stepsize = std::max(next_biggest_stepsize, vert_step);
                }
                biggest_stepsize = next_biggest_stepsize;

                if (num_changing_childs == 0 && (flags & NC_BIGFIRST) && biggest_stepsize > 0) {
                        /* Second.5 loop: count how many children are of the updated biggest step size. */
                        for (const auto &child_wid : this->children) {
                                uint vert_step = child_wid->GetVerticalStepSize(sizing);
                                if (vert_step == biggest_stepsize) {
                                        num_changing_childs++;
                                }
                        }
                }
        }
        assert(num_changing_childs == 0);

        uint pre = this->pip_pre;
        uint inter = this->pip_inter;

        if (additional_length > 0) {
                /* Allocate remaining space by pip ratios. If this doesn't round exactly, the unused space will fall into pip_post
                 * which is never explicitly needed. */
                int r = this->pip_ratio_pre + this->gaps * this->pip_ratio_inter + this->pip_ratio_post;
                if (r > 0) {
                        pre += this->pip_ratio_pre * additional_length / r;
                        if (this->gaps > 0) inter += this->pip_ratio_inter * additional_length / r;
                }
        }

        /* Third loop: Compute position and call the child. */
        uint position = pre; // Place to put next child relative to origin of the container.
        for (const auto &child_wid : this->children) {
                uint child_x = x + (rtl ? child_wid->padding.right : child_wid->padding.left);
                uint child_height = child_wid->current_y;

                child_wid->AssignSizePosition(sizing, child_x, y + position + child_wid->padding.top, child_wid->current_x, child_height, rtl);
                if (child_wid->current_y != 0) {
                        position += child_height + child_wid->padding.Vertical() + inter;
                }
        }
}

/**
 * Generic spacer widget.
 * @param width  Horizontal size of the spacer widget.
 * @param height Vertical size of the spacer widget.
 */
NWidgetSpacer::NWidgetSpacer(int width, int height) : NWidgetResizeBase(NWID_SPACER, 0, 0)
{
        this->SetMinimalSize(width, height);
        this->SetResize(0, 0);
}

void NWidgetSpacer::SetupSmallestSize(Window *)
{
        this->smallest_x = this->min_x;
        this->smallest_y = this->min_y;
        this->ApplyAspectRatio();
}

void NWidgetSpacer::FillWidgetLookup(WidgetLookup &)
{
}

void NWidgetSpacer::Draw(const Window *w)
{
        /* Spacer widget is never normally visible. */

        if (_draw_widget_outlines && this->current_x != 0 && this->current_y != 0) {
                /* Spacers indicate a potential design issue, so get extra highlighting. */
                GfxFillRect(this->GetCurrentRect(), PC_WHITE, FILLRECT_CHECKER);

                DrawOutline(w, this);
        }
}

void NWidgetSpacer::SetDirty(const Window *) const
{
        /* Spacer widget never need repainting. */
}

NWidgetCore *NWidgetSpacer::GetWidgetFromPos(int, int)
{
        return nullptr;
}

NWidgetMatrix::NWidgetMatrix(Colours colour, WidgetID index) : NWidgetPIPContainer(NWID_MATRIX, NC_EQUALSIZE), index(index), clicked(-1), count(-1)
{
        this->colour = colour;
}

/**
 * Sets the clicked element in the matrix.
 * @param clicked The clicked element.
 */
void NWidgetMatrix::SetClicked(int clicked)
{
        this->clicked = clicked;
        if (this->clicked >= 0 && this->sb != nullptr && this->widgets_x != 0) {
                int vpos = (this->clicked / this->widgets_x) * this->widget_h; // Vertical position of the top.
                /* Need to scroll down -> Scroll to the bottom.
                 * However, last entry has no 'this->pip_inter' underneath, and we must stay below this->sb->GetCount() */
                if (this->sb->GetPosition() < vpos) vpos += this->widget_h - this->pip_inter - 1;
                this->sb->ScrollTowards(vpos);
        }
}

/**
 * Set the number of elements in this matrix.
 * @note Updates the number of elements/capacity of the real scrollbar.
 * @param count The number of elements.
 */
void NWidgetMatrix::SetCount(int count)
{
        this->count = count;

        if (this->sb == nullptr || this->widgets_x == 0) return;

        /* We need to get the number of pixels the matrix is high/wide.
         * So, determine the number of rows/columns based on the number of
         * columns/rows (one is constant/unscrollable).
         * Then multiply that by the height of a widget, and add the pre
         * and post spacing "offsets". */
        count = CeilDiv(count, this->sb->IsVertical() ? this->widgets_x : this->widgets_y);
        count *= (this->sb->IsVertical() ? this->children.front()->smallest_y : this->children.front()->smallest_x) + this->pip_inter;
        if (count > 0) count -= this->pip_inter; // We counted an inter too much in the multiplication above
        count += this->pip_pre + this->pip_post;
        this->sb->SetCount(count);
        this->sb->SetCapacity(this->sb->IsVertical() ? this->current_y : this->current_x);
        this->sb->SetStepSize(this->sb->IsVertical() ? this->widget_h  : this->widget_w);
}

/**
 * Assign a scrollbar to this matrix.
 * @param sb The scrollbar to assign to us.
 */
void NWidgetMatrix::SetScrollbar(Scrollbar *sb)
{
        this->sb = sb;
}

/**
 * Get current element.
 * @returns index of current element.
 */
int NWidgetMatrix::GetCurrentElement() const
{
        return this->current_element;
}

void NWidgetMatrix::SetupSmallestSize(Window *w)
{
        assert(this->children.size() == 1);

        this->children.front()->SetupSmallestSize(w);

        Dimension padding = { (uint)this->pip_pre + this->pip_post, (uint)this->pip_pre + this->pip_post};
        Dimension size    = {this->children.front()->smallest_x + padding.width, this->children.front()->smallest_y + padding.height};
        Dimension fill    = {0, 0};
        Dimension resize  = {this->pip_inter + this->children.front()->smallest_x, this->pip_inter + this->children.front()->smallest_y};

        if (this->index >= 0) w->UpdateWidgetSize(this->index, size, padding, fill, resize);

        this->smallest_x = size.width;
        this->smallest_y = size.height;
        this->fill_x = fill.width;
        this->fill_y = fill.height;
        this->resize_x = resize.width;
        this->resize_y = resize.height;
        this->ApplyAspectRatio();
}

void NWidgetMatrix::AssignSizePosition(SizingType, int x, int y, uint given_width, uint given_height, bool)
{
        assert(given_width >= this->smallest_x && given_height >= this->smallest_y);

        this->pos_x = x;
        this->pos_y = y;
        this->current_x = given_width;
        this->current_y = given_height;

        /* Determine the size of the widgets, and the number of visible widgets on each of the axis. */
        this->widget_w = this->children.front()->smallest_x + this->pip_inter;
        this->widget_h = this->children.front()->smallest_y + this->pip_inter;

        /* Account for the pip_inter is between widgets, so we need to account for that when
         * the division assumes pip_inter is used for all widgets. */
        this->widgets_x = CeilDiv(this->current_x - this->pip_pre - this->pip_post + this->pip_inter, this->widget_w);
        this->widgets_y = CeilDiv(this->current_y - this->pip_pre - this->pip_post + this->pip_inter, this->widget_h);

        /* When resizing, update the scrollbar's count. E.g. with a vertical
         * scrollbar becoming wider or narrower means the amount of rows in
         * the scrollbar becomes respectively smaller or higher. */
        this->SetCount(this->count);
}

void NWidgetMatrix::FillWidgetLookup(WidgetLookup &widget_lookup)
{
        if (this->index >= 0) widget_lookup[this->index] = this;
        NWidgetContainer::FillWidgetLookup(widget_lookup);
}

NWidgetCore *NWidgetMatrix::GetWidgetFromPos(int x, int y)
{
        /* Falls outside of the matrix widget. */
        if (!IsInsideBS(x, this->pos_x, this->current_x) || !IsInsideBS(y, this->pos_y, this->current_y)) return nullptr;

        int start_x, start_y, base_offs_x, base_offs_y;
        this->GetScrollOffsets(start_x, start_y, base_offs_x, base_offs_y);

        bool rtl = _current_text_dir == TD_RTL;

        int widget_col = (rtl ?
                                -x + (int)this->pip_post + this->pos_x + base_offs_x + this->widget_w - 1 - (int)this->pip_inter :
                                 x - (int)this->pip_pre  - this->pos_x - base_offs_x
                        ) / this->widget_w;

        int widget_row = (y - base_offs_y - (int)this->pip_pre - this->pos_y) / this->widget_h;

        this->current_element = (widget_row + start_y) * this->widgets_x + start_x + widget_col;
        if (this->current_element >= this->count) return nullptr;

        NWidgetCore *child = dynamic_cast<NWidgetCore *>(this->children.front().get());
        assert(child != nullptr);
        child->AssignSizePosition(ST_RESIZE,
                        this->pos_x + (rtl ? this->pip_post - widget_col * this->widget_w : this->pip_pre + widget_col * this->widget_w) + base_offs_x,
                        this->pos_y + this->pip_pre + widget_row * this->widget_h + base_offs_y,
                        child->smallest_x, child->smallest_y, rtl);

        return child->GetWidgetFromPos(x, y);
}

/* virtual */ void NWidgetMatrix::Draw(const Window *w)
{
        /* Fill the background. */
        GfxFillRect(this->GetCurrentRect(), GetColourGradient(this->colour, SHADE_LIGHT));

        /* Set up a clipping area for the previews. */
        bool rtl = _current_text_dir == TD_RTL;
        DrawPixelInfo tmp_dpi;
        if (!FillDrawPixelInfo(&tmp_dpi, this->pos_x + (rtl ? this->pip_post : this->pip_pre), this->pos_y + this->pip_pre, this->current_x - this->pip_pre - this->pip_post, this->current_y - this->pip_pre - this->pip_post)) return;

        {
                AutoRestoreBackup dpi_backup(_cur_dpi, &tmp_dpi);

                /* Get the appropriate offsets so we can draw the right widgets. */
                NWidgetCore *child = dynamic_cast<NWidgetCore *>(this->children.front().get());
                assert(child != nullptr);
                int start_x, start_y, base_offs_x, base_offs_y;
                this->GetScrollOffsets(start_x, start_y, base_offs_x, base_offs_y);

                int offs_y = base_offs_y;
                for (int y = start_y; y < start_y + this->widgets_y + 1; y++, offs_y += this->widget_h) {
                        /* Are we within bounds? */
                        if (offs_y + child->smallest_y <= 0) continue;
                        if (offs_y >= (int)this->current_y) break;

                        /* We've passed our amount of widgets. */
                        if (y * this->widgets_x >= this->count) break;

                        int offs_x = base_offs_x;
                        for (int x = start_x; x < start_x + this->widgets_x + 1; x++, offs_x += rtl ? -this->widget_w : this->widget_w) {
                                /* Are we within bounds? */
                                if (offs_x + child->smallest_x <= 0) continue;
                                if (offs_x >= (int)this->current_x) continue;

                                /* Do we have this many widgets? */
                                this->current_element = y * this->widgets_x + x;
                                if (this->current_element >= this->count) break;

                                child->AssignSizePosition(ST_RESIZE, offs_x, offs_y, child->smallest_x, child->smallest_y, rtl);
                                child->SetLowered(this->clicked == this->current_element);
                                child->Draw(w);
                        }
                }
        }

        DrawOutline(w, this);
}

/**
 * Get the different offsets that are influenced by scrolling.
 * @param[out] start_x     The start position in columns (index of the left-most column, swapped in RTL).
 * @param[out] start_y     The start position in rows.
 * @param[out] base_offs_x The base horizontal offset in pixels (X position of the column \a start_x).
 * @param[out] base_offs_y The base vertical offset in pixels (Y position of the column \a start_y).
 */
void NWidgetMatrix::GetScrollOffsets(int &start_x, int &start_y, int &base_offs_x, int &base_offs_y)
{
        base_offs_x = _current_text_dir == TD_RTL ? this->widget_w * (this->widgets_x - 1) : 0;
        base_offs_y = 0;
        start_x = 0;
        start_y = 0;
        if (this->sb != nullptr) {
                if (this->sb->IsVertical()) {
                        start_y = this->sb->GetPosition() / this->widget_h;
                        base_offs_y += -this->sb->GetPosition() + start_y * this->widget_h;
                } else {
                        start_x = this->sb->GetPosition() / this->widget_w;
                        int sub_x = this->sb->GetPosition() - start_x * this->widget_w;
                        if (_current_text_dir == TD_RTL) {
                                base_offs_x += sub_x;
                        } else {
                                base_offs_x -= sub_x;
                        }
                }
        }
}

/**
 * Constructor parent nested widgets.
 * @param tp     Type of parent widget.
 * @param colour Colour of the parent widget.
 * @param index  Index of the widget.
 * @param child  Child container widget (if supplied). If not supplied, a
 *               vertical container will be inserted while adding the first
 *               child widget.
 */
NWidgetBackground::NWidgetBackground(WidgetType tp, Colours colour, WidgetID index, std::unique_ptr<NWidgetPIPContainer> &&child) : NWidgetCore(tp, colour, index, 1, 1, 0x0, STR_NULL)
{
        assert(tp == WWT_PANEL || tp == WWT_INSET || tp == WWT_FRAME);
        this->child = std::move(child);
        if (this->child != nullptr) this->child->parent = this;
        this->SetAlignment(SA_TOP | SA_LEFT);
}

/**
 * Add a child to the parent.
 * @param nwid Nested widget to add to the background widget.
 *
 * Unless a child container has been given in the constructor, a parent behaves as a vertical container.
 * You can add several children to it, and they are put underneath each other.
 */
void NWidgetBackground::Add(std::unique_ptr<NWidgetBase> &&nwid)
{
        if (this->child == nullptr) {
                this->child = std::make_unique<NWidgetVertical>();
        }
        nwid->parent = this->child.get();
        this->child->Add(std::move(nwid));
}

/**
 * Set additional pre/inter/post space for the background widget.
 *
 * @param pip_pre   Additional space in front of the first child widget (above
 *                  for the vertical container, at the left for the horizontal container).
 * @param pip_inter Additional space between two child widgets.
 * @param pip_post  Additional space after the last child widget (below for the
 *                  vertical container, at the right for the horizontal container).
 * @note Using this function implies that the widget has (or will have) child widgets.
 */
void NWidgetBackground::SetPIP(uint8_t pip_pre, uint8_t pip_inter, uint8_t pip_post)
{
        if (this->child == nullptr) {
                this->child = std::make_unique<NWidgetVertical>();
        }
        this->child->parent = this;
        this->child->SetPIP(pip_pre, pip_inter, pip_post);
}

/**
 * Set additional pre/inter/post space ratios for the background widget.
 *
 * @param pip_ratio_pre   Ratio of additional space in front of the first child widget (above
 *                        for the vertical container, at the left for the horizontal container).
 * @param pip_ratio_inter Ratio of additional space between two child widgets.
 * @param pip_ratio_post  Ratio of additional space after the last child widget (below for the
 *                        vertical container, at the right for the horizontal container).
 * @note Using this function implies that the widget has (or will have) child widgets.
 */
void NWidgetBackground::SetPIPRatio(uint8_t pip_ratio_pre, uint8_t pip_ratio_inter, uint8_t pip_ratio_post)
{
        if (this->child == nullptr) {
                this->child = std::make_unique<NWidgetVertical>();
        }
        this->child->parent = this;
        this->child->SetPIPRatio(pip_ratio_pre, pip_ratio_inter, pip_ratio_post);
}

void NWidgetBackground::AdjustPaddingForZoom()
{
        if (child != nullptr) child->AdjustPaddingForZoom();
        NWidgetCore::AdjustPaddingForZoom();
}

void NWidgetBackground::SetupSmallestSize(Window *w)
{
        if (this->child != nullptr) {
                this->child->SetupSmallestSize(w);

                this->smallest_x = this->child->smallest_x;
                this->smallest_y = this->child->smallest_y;
                this->fill_x = this->child->fill_x;
                this->fill_y = this->child->fill_y;
                this->resize_x = this->child->resize_x;
                this->resize_y = this->child->resize_y;

                /* Don't apply automatic padding if there is no child widget. */
                if (w == nullptr) return;

                if (this->type == WWT_FRAME) {
                        /* Account for the size of the frame's text if that exists */
                        this->child->padding     = WidgetDimensions::scaled.frametext;
                        this->child->padding.top = std::max<uint8_t>(WidgetDimensions::scaled.frametext.top, this->widget_data != STR_NULL ? GetCharacterHeight(FS_NORMAL) + WidgetDimensions::scaled.frametext.top / 2 : 0);

                        this->smallest_x += this->child->padding.Horizontal();
                        this->smallest_y += this->child->padding.Vertical();

                        if (this->index >= 0) w->SetStringParameters(this->index);
                        this->smallest_x = std::max(this->smallest_x, GetStringBoundingBox(this->widget_data, this->text_size).width + WidgetDimensions::scaled.frametext.Horizontal());
                } else if (this->type == WWT_INSET) {
                        /* Apply automatic padding for bevel thickness. */
                        this->child->padding = WidgetDimensions::scaled.bevel;

                        this->smallest_x += this->child->padding.Horizontal();
                        this->smallest_y += this->child->padding.Vertical();
                }
                this->ApplyAspectRatio();
        } else {
                Dimension d = {this->min_x, this->min_y};
                Dimension fill = {this->fill_x, this->fill_y};
                Dimension resize  = {this->resize_x, this->resize_y};
                if (w != nullptr) { // A non-nullptr window pointer acts as switch to turn dynamic widget size on.
                        if (this->type == WWT_FRAME || this->type == WWT_INSET) {
                                if (this->index >= 0) w->SetStringParameters(this->index);
                                Dimension background = GetStringBoundingBox(this->widget_data, this->text_size);
                                background.width += (this->type == WWT_FRAME) ? (WidgetDimensions::scaled.frametext.Horizontal()) : (WidgetDimensions::scaled.inset.Horizontal());
                                d = maxdim(d, background);
                        }
                        if (this->index >= 0) {
                                Dimension padding;
                                switch (this->type) {
                                        default: NOT_REACHED();
                                        case WWT_PANEL: padding = {WidgetDimensions::scaled.framerect.Horizontal(), WidgetDimensions::scaled.framerect.Vertical()}; break;
                                        case WWT_FRAME: padding = {WidgetDimensions::scaled.frametext.Horizontal(), WidgetDimensions::scaled.frametext.Vertical()}; break;
                                        case WWT_INSET: padding = {WidgetDimensions::scaled.inset.Horizontal(),     WidgetDimensions::scaled.inset.Vertical()};     break;
                                }
                                w->UpdateWidgetSize(this->index, d, padding, fill, resize);
                        }
                }
                this->smallest_x = d.width;
                this->smallest_y = d.height;
                this->fill_x = fill.width;
                this->fill_y = fill.height;
                this->resize_x = resize.width;
                this->resize_y = resize.height;
                this->ApplyAspectRatio();
        }
}

void NWidgetBackground::AssignSizePosition(SizingType sizing, int x, int y, uint given_width, uint given_height, bool rtl)
{
        this->StoreSizePosition(sizing, x, y, given_width, given_height);

        if (this->child != nullptr) {
                uint x_offset = (rtl ? this->child->padding.right : this->child->padding.left);
                uint width = given_width - this->child->padding.Horizontal();
                uint height = given_height - this->child->padding.Vertical();
                this->child->AssignSizePosition(sizing, x + x_offset, y + this->child->padding.top, width, height, rtl);
        }
}

void NWidgetBackground::FillWidgetLookup(WidgetLookup &widget_lookup)
{
        if (this->index >= 0) widget_lookup[this->index] = this;
        if (this->child != nullptr) this->child->FillWidgetLookup(widget_lookup);
}

void NWidgetBackground::Draw(const Window *w)
{
        if (this->current_x == 0 || this->current_y == 0) return;

        Rect r = this->GetCurrentRect();

        const DrawPixelInfo *dpi = _cur_dpi;
        if (dpi->left > r.right || dpi->left + dpi->width <= r.left || dpi->top > r.bottom || dpi->top + dpi->height <= r.top) return;

        switch (this->type) {
                case WWT_PANEL:
                        assert(this->widget_data == 0);
                        DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, this->IsLowered() ? FR_LOWERED : FR_NONE);
                        break;

                case WWT_FRAME:
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        DrawFrame(r, this->colour, this->text_colour, this->widget_data, this->align, this->text_size);
                        break;

                case WWT_INSET:
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        DrawInset(r, this->colour, this->text_colour, this->widget_data, this->align, this->text_size);
                        break;

                default:
                        NOT_REACHED();
        }

        if (this->index >= 0) w->DrawWidget(r, this->index);
        if (this->child != nullptr) this->child->Draw(w);

        if (this->IsDisabled()) {
                GfxFillRect(r.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(this->colour, SHADE_DARKER), FILLRECT_CHECKER);
        }

        DrawOutline(w, this);
}

NWidgetCore *NWidgetBackground::GetWidgetFromPos(int x, int y)
{
        NWidgetCore *nwid = nullptr;
        if (IsInsideBS(x, this->pos_x, this->current_x) && IsInsideBS(y, this->pos_y, this->current_y)) {
                if (this->child != nullptr) nwid = this->child->GetWidgetFromPos(x, y);
                if (nwid == nullptr) nwid = this;
        }
        return nwid;
}

NWidgetBase *NWidgetBackground::GetWidgetOfType(WidgetType tp)
{
        NWidgetBase *nwid = nullptr;
        if (this->child != nullptr) nwid = this->child->GetWidgetOfType(tp);
        if (nwid == nullptr && this->type == tp) nwid = this;
        return nwid;
}

NWidgetViewport::NWidgetViewport(WidgetID index) : NWidgetCore(NWID_VIEWPORT, INVALID_COLOUR, index, 1, 1, 0x0, STR_NULL)
{
}

void NWidgetViewport::SetupSmallestSize(Window *)
{
        this->smallest_x = this->min_x;
        this->smallest_y = this->min_y;
        this->ApplyAspectRatio();
}

void NWidgetViewport::Draw(const Window *w)
{
        if (this->current_x == 0 || this->current_y == 0) return;

        if (this->disp_flags & ND_NO_TRANSPARENCY) {
                TransparencyOptionBits to_backup = _transparency_opt;
                _transparency_opt &= (1 << TO_SIGNS) | (1 << TO_TEXT); // Disable all transparency, except textual stuff
                w->DrawViewport();
                _transparency_opt = to_backup;
        } else {
                w->DrawViewport();
        }

        /* Optionally shade the viewport. */
        if (this->disp_flags & (ND_SHADE_GREY | ND_SHADE_DIMMED)) {
                GfxFillRect(this->GetCurrentRect(), (this->disp_flags & ND_SHADE_DIMMED) ? PALETTE_TO_TRANSPARENT : PALETTE_NEWSPAPER, FILLRECT_RECOLOUR);
        }

        DrawOutline(w, this);
}

/**
 * Initialize the viewport of the window.
 * @param w            Window owning the viewport.
 * @param focus        Either the tile index or vehicle ID to focus.
 * @param zoom         Zoom level.
 */
void NWidgetViewport::InitializeViewport(Window *w, std::variant<TileIndex, VehicleID> focus, ZoomLevel zoom)
{
        InitializeWindowViewport(w, this->pos_x, this->pos_y, this->current_x, this->current_y, focus, zoom);
}

/**
 * Update the position and size of the viewport (after eg a resize).
 * @param w Window owning the viewport.
 */
void NWidgetViewport::UpdateViewportCoordinates(Window *w)
{
        Viewport *vp = w->viewport;
        if (vp != nullptr) {
                vp->left = w->left + this->pos_x;
                vp->top  = w->top + this->pos_y;
                vp->width  = this->current_x;
                vp->height = this->current_y;

                vp->virtual_width  = ScaleByZoom(vp->width, vp->zoom);
                vp->virtual_height = ScaleByZoom(vp->height, vp->zoom);
        }
}

/**
 * Compute the row of a scrolled widget that a user clicked in.
 * @param clickpos    Vertical position of the mouse click (without taking scrolling into account).
 * @param w           The window the click was in.
 * @param widget      Widget number of the widget clicked in.
 * @param padding     Amount of empty space between the widget edge and the top of the first row. Default value is \c 0.
 * @param line_height Height of a single row. A negative value means using the vertical resize step of the widget.
 * @return Row number clicked at. If clicked at a wrong position, #Scrollbar::npos is returned.
 */
Scrollbar::size_type Scrollbar::GetScrolledRowFromWidget(int clickpos, const Window * const w, WidgetID widget, int padding, int line_height) const
{
        int pos = w->GetRowFromWidget(clickpos, widget, padding, line_height);
        if (pos != INT_MAX) pos += this->GetPosition();
        return (pos < 0 || pos >= this->GetCount()) ? Scrollbar::npos : pos;
}

/**
 * Update the given list position as if it were on this scroll bar when the given keycode was pressed.
 * This does not update the actual position of this scroll bar, that is left to the caller. It does,
 * however use the capacity and count of the scroll bar for the bounds and amount to scroll.
 *
 * When the count is 0 or the return is ES_NOT_HANDLED, then the position is not updated.
 * With WKC_UP and WKC_DOWN the position goes one up or down respectively.
 * With WKC_PAGEUP and WKC_PAGEDOWN the position goes one capacity up or down respectively.
 * With WKC_HOME the first position is selected and with WKC_END the last position is selected.
 * This function ensures that pos is in the range [0..count).
 * @param list_position The current position in the list.
 * @param key_code      The pressed key code.
 * @return ES_NOT_HANDLED when another key than the 6 specific keys was pressed, otherwise ES_HANDLED.
 */
EventState Scrollbar::UpdateListPositionOnKeyPress(int &list_position, uint16_t keycode) const
{
        int new_pos = list_position;
        switch (keycode) {
                case WKC_UP:
                        /* scroll up by one */
                        new_pos--;
                        break;

                case WKC_DOWN:
                        /* scroll down by one */
                        new_pos++;
                        break;

                case WKC_PAGEUP:
                        /* scroll up a page */
                        new_pos -= this->GetCapacity();
                        break;

                case WKC_PAGEDOWN:
                        /* scroll down a page */
                        new_pos += this->GetCapacity();
                        break;

                case WKC_HOME:
                        /* jump to beginning */
                        new_pos = 0;
                        break;

                case WKC_END:
                        /* jump to end */
                        new_pos = this->GetCount() - 1;
                        break;

                default:
                        return ES_NOT_HANDLED;
        }

        /* If there are no elements, there is nothing to scroll/update. */
        if (this->GetCount() != 0) {
                list_position = Clamp(new_pos, 0, this->GetCount() - 1);
        }
        return ES_HANDLED;
}


/**
 * Set capacity of visible elements from the size and resize properties of a widget.
 * @param w       Window.
 * @param widget  Widget with size and resize properties.
 * @param padding Padding to subtract from the size.
 * @note Updates the position if needed.
 */
void Scrollbar::SetCapacityFromWidget(Window *w, WidgetID widget, int padding)
{
        NWidgetBase *nwid = w->GetWidget<NWidgetBase>(widget);
        if (this->IsVertical()) {
                this->SetCapacity(((int)nwid->current_y - padding) / (int)nwid->resize_y);
        } else {
                this->SetCapacity(((int)nwid->current_x - padding) / (int)nwid->resize_x);
        }
}

/**
 * Apply 'scroll' to a rect to be drawn in.
 * @param r Rect to be 'scrolled'.
 * @param sb The scrollbar affecting the scroll.
 * @param resize_step Resize step of the widget/scrollbar (1 if the scrollbar is pixel-based.)
 * @returns Scrolled rect.
 */
Rect ScrollRect(Rect r, const Scrollbar &sb, int resize_step)
{
        const int count = sb.GetCount() * resize_step;
        const int position = sb.GetPosition() * resize_step;

        if (sb.IsVertical()) {
                r.top -= position;
                r.bottom = r.top + count;
        } else {
                bool rtl = _current_text_dir == TD_RTL;
                if (rtl) {
                        r.right += position;
                        r.left = r.right - count;
                } else {
                        r.left -= position;
                        r.right = r.left + count;
                }
        }

        return r;
}

/**
 * Scrollbar widget.
 * @param tp     Scrollbar type. (horizontal/vertical)
 * @param colour Colour of the scrollbar.
 * @param index  Index of the widget.
 */
NWidgetScrollbar::NWidgetScrollbar(WidgetType tp, Colours colour, WidgetID index) : NWidgetCore(tp, colour, index, 1, 1, 0x0, STR_NULL), Scrollbar(tp != NWID_HSCROLLBAR)
{
        assert(tp == NWID_HSCROLLBAR || tp == NWID_VSCROLLBAR);

        switch (this->type) {
                case NWID_HSCROLLBAR:
                        this->SetResize(1, 0);
                        this->SetFill(1, 0);
                        this->SetDataTip(0x0, STR_TOOLTIP_HSCROLL_BAR_SCROLLS_LIST);
                        break;

                case NWID_VSCROLLBAR:
                        this->SetResize(0, 1);
                        this->SetFill(0, 1);
                        this->SetDataTip(0x0, STR_TOOLTIP_VSCROLL_BAR_SCROLLS_LIST);
                        break;

                default: NOT_REACHED();
        }
}

void NWidgetScrollbar::SetupSmallestSize(Window *)
{
        this->min_x = 0;
        this->min_y = 0;

        switch (this->type) {
                case NWID_HSCROLLBAR:
                        this->SetMinimalSizeAbsolute(NWidgetScrollbar::GetHorizontalDimension().width * 3, NWidgetScrollbar::GetHorizontalDimension().height);
                        break;

                case NWID_VSCROLLBAR:
                        this->SetMinimalSizeAbsolute(NWidgetScrollbar::GetVerticalDimension().width, NWidgetScrollbar::GetVerticalDimension().height * 3);
                        break;

                default: NOT_REACHED();
        }

        this->smallest_x = this->min_x;
        this->smallest_y = this->min_y;
}

void NWidgetScrollbar::Draw(const Window *w)
{
        if (this->current_x == 0 || this->current_y == 0) return;

        Rect r = this->GetCurrentRect();

        const DrawPixelInfo *dpi = _cur_dpi;
        if (dpi->left > r.right || dpi->left + dpi->width <= r.left || dpi->top > r.bottom || dpi->top + dpi->height <= r.top) return;

        bool up_lowered = HasBit(this->disp_flags, NDB_SCROLLBAR_UP);
        bool down_lowered = HasBit(this->disp_flags, NDB_SCROLLBAR_DOWN);
        bool middle_lowered = !(this->disp_flags & ND_SCROLLBAR_BTN) && w->mouse_capture_widget == this->index;

        if (this->type == NWID_HSCROLLBAR) {
                DrawHorizontalScrollbar(r, this->colour, up_lowered, middle_lowered, down_lowered, this);
        } else {
                DrawVerticalScrollbar(r, this->colour, up_lowered, middle_lowered, down_lowered, this);
        }

        if (this->IsDisabled()) {
                GfxFillRect(r.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(this->colour, SHADE_DARKER), FILLRECT_CHECKER);
        }

        DrawOutline(w, this);
}

/* static */ void NWidgetScrollbar::InvalidateDimensionCache()
{
        vertical_dimension.width   = vertical_dimension.height   = 0;
        horizontal_dimension.width = horizontal_dimension.height = 0;
}

/* static */ Dimension NWidgetScrollbar::GetVerticalDimension()
{
        if (vertical_dimension.width == 0) {
                vertical_dimension = maxdim(GetScaledSpriteSize(SPR_ARROW_UP), GetScaledSpriteSize(SPR_ARROW_DOWN));
                vertical_dimension.width += WidgetDimensions::scaled.vscrollbar.Horizontal();
                vertical_dimension.height += WidgetDimensions::scaled.vscrollbar.Vertical();
        }
        return vertical_dimension;
}

/* static */ Dimension NWidgetScrollbar::GetHorizontalDimension()
{
        if (horizontal_dimension.width == 0) {
                horizontal_dimension = maxdim(GetScaledSpriteSize(SPR_ARROW_LEFT), GetScaledSpriteSize(SPR_ARROW_RIGHT));
                horizontal_dimension.width += WidgetDimensions::scaled.hscrollbar.Horizontal();
                horizontal_dimension.height += WidgetDimensions::scaled.hscrollbar.Vertical();
        }
        return horizontal_dimension;
}

Dimension NWidgetScrollbar::vertical_dimension = {0, 0};
Dimension NWidgetScrollbar::horizontal_dimension = {0, 0};

/** Reset the cached dimensions. */
/* static */ void NWidgetLeaf::InvalidateDimensionCache()
{
        shadebox_dimension.width   = shadebox_dimension.height   = 0;
        debugbox_dimension.width   = debugbox_dimension.height   = 0;
        defsizebox_dimension.width = defsizebox_dimension.height = 0;
        stickybox_dimension.width  = stickybox_dimension.height  = 0;
        resizebox_dimension.width  = resizebox_dimension.height  = 0;
        closebox_dimension.width   = closebox_dimension.height   = 0;
        dropdown_dimension.width   = dropdown_dimension.height   = 0;
}

Dimension NWidgetLeaf::shadebox_dimension   = {0, 0};
Dimension NWidgetLeaf::debugbox_dimension   = {0, 0};
Dimension NWidgetLeaf::defsizebox_dimension = {0, 0};
Dimension NWidgetLeaf::stickybox_dimension  = {0, 0};
Dimension NWidgetLeaf::resizebox_dimension  = {0, 0};
Dimension NWidgetLeaf::closebox_dimension   = {0, 0};
Dimension NWidgetLeaf::dropdown_dimension   = {0, 0};

/**
 * Nested leaf widget.
 * @param tp     Type of leaf widget.
 * @param colour Colour of the leaf widget.
 * @param index  Index of the widget.
 * @param data   Data of the widget.
 * @param tip    Tooltip of the widget.
 */
NWidgetLeaf::NWidgetLeaf(WidgetType tp, Colours colour, WidgetID index, uint32_t data, StringID tip) : NWidgetCore(tp, colour, index, 1, 1, data, tip)
{
        assert(index >= 0 || tp == WWT_LABEL || tp == WWT_TEXT || tp == WWT_CAPTION || tp == WWT_RESIZEBOX || tp == WWT_SHADEBOX || tp == WWT_DEFSIZEBOX || tp == WWT_DEBUGBOX || tp == WWT_STICKYBOX || tp == WWT_CLOSEBOX);
        this->min_x = 0;
        this->min_y = 0;
        this->SetResize(0, 0);

        switch (tp) {
                case WWT_EMPTY:
                        break;

                case WWT_TEXT:
                        this->SetFill(0, 0);
                        this->SetAlignment(SA_LEFT | SA_VERT_CENTER);
                        break;

                case WWT_PUSHBTN:
                case WWT_IMGBTN:
                case WWT_PUSHIMGBTN:
                case WWT_IMGBTN_2:
                case WWT_TEXTBTN:
                case WWT_PUSHTXTBTN:
                case WWT_TEXTBTN_2:
                case WWT_LABEL:
                case WWT_MATRIX:
                case NWID_BUTTON_DROPDOWN:
                case NWID_PUSHBUTTON_DROPDOWN:
                        this->SetFill(0, 0);
                        break;

                case WWT_ARROWBTN:
                case WWT_PUSHARROWBTN:
                        this->SetFill(0, 0);
                        this->SetAspect(WidgetDimensions::ASPECT_LEFT_RIGHT_BUTTON);
                        break;

                case WWT_EDITBOX:
                        this->SetFill(0, 0);
                        break;

                case WWT_CAPTION:
                        this->SetFill(1, 0);
                        this->SetResize(1, 0);
                        this->SetMinimalSize(0, WidgetDimensions::WD_CAPTION_HEIGHT);
                        this->SetMinimalTextLines(1, WidgetDimensions::unscaled.captiontext.Vertical(), FS_NORMAL);
                        this->SetDataTip(data, STR_TOOLTIP_WINDOW_TITLE_DRAG_THIS);
                        break;

                case WWT_STICKYBOX:
                        this->SetFill(0, 0);
                        this->SetMinimalSize(WidgetDimensions::WD_STICKYBOX_WIDTH, WidgetDimensions::WD_CAPTION_HEIGHT);
                        this->SetDataTip(STR_NULL, STR_TOOLTIP_STICKY);
                        this->SetAspect(this->min_x, this->min_y);
                        break;

                case WWT_SHADEBOX:
                        this->SetFill(0, 0);
                        this->SetMinimalSize(WidgetDimensions::WD_SHADEBOX_WIDTH, WidgetDimensions::WD_CAPTION_HEIGHT);
                        this->SetDataTip(STR_NULL, STR_TOOLTIP_SHADE);
                        this->SetAspect(this->min_x, this->min_y);
                        break;

                case WWT_DEBUGBOX:
                        this->SetFill(0, 0);
                        this->SetMinimalSize(WidgetDimensions::WD_DEBUGBOX_WIDTH, WidgetDimensions::WD_CAPTION_HEIGHT);
                        this->SetDataTip(STR_NULL, STR_TOOLTIP_DEBUG);
                        this->SetAspect(this->min_x, this->min_y);
                        break;

                case WWT_DEFSIZEBOX:
                        this->SetFill(0, 0);
                        this->SetMinimalSize(WidgetDimensions::WD_DEFSIZEBOX_WIDTH, WidgetDimensions::WD_CAPTION_HEIGHT);
                        this->SetDataTip(STR_NULL, STR_TOOLTIP_DEFSIZE);
                        this->SetAspect(this->min_x, this->min_y);
                        break;

                case WWT_RESIZEBOX:
                        this->SetFill(0, 0);
                        this->SetMinimalSize(WidgetDimensions::WD_RESIZEBOX_WIDTH, 12);
                        this->SetDataTip(RWV_SHOW_BEVEL, STR_TOOLTIP_RESIZE);
                        break;

                case WWT_CLOSEBOX:
                        this->SetFill(0, 0);
                        this->SetMinimalSize(WidgetDimensions::WD_CLOSEBOX_WIDTH, WidgetDimensions::WD_CAPTION_HEIGHT);
                        this->SetDataTip(STR_NULL, STR_TOOLTIP_CLOSE_WINDOW);
                        this->SetAspect(this->min_x, this->min_y);
                        break;

                case WWT_DROPDOWN:
                        this->SetFill(0, 0);
                        this->SetMinimalSize(0, WidgetDimensions::WD_DROPDOWN_HEIGHT);
                        this->SetAlignment(SA_TOP | SA_LEFT);
                        break;

                default:
                        NOT_REACHED();
        }
}

void NWidgetLeaf::SetupSmallestSize(Window *w)
{
        Dimension padding = {0, 0};
        Dimension size = {this->min_x, this->min_y};
        Dimension fill = {this->fill_x, this->fill_y};
        Dimension resize = {this->resize_x, this->resize_y};
        switch (this->type) {
                case WWT_EMPTY: {
                        break;
                }
                case WWT_MATRIX: {
                        padding = {WidgetDimensions::scaled.matrix.Horizontal(), WidgetDimensions::scaled.matrix.Vertical()};
                        break;
                }
                case WWT_SHADEBOX: {
                        padding = {WidgetDimensions::scaled.shadebox.Horizontal(), WidgetDimensions::scaled.shadebox.Vertical()};
                        if (NWidgetLeaf::shadebox_dimension.width == 0) {
                                NWidgetLeaf::shadebox_dimension = maxdim(GetScaledSpriteSize(SPR_WINDOW_SHADE), GetScaledSpriteSize(SPR_WINDOW_UNSHADE));
                                NWidgetLeaf::shadebox_dimension.width += padding.width;
                                NWidgetLeaf::shadebox_dimension.height += padding.height;
                        }
                        size = maxdim(size, NWidgetLeaf::shadebox_dimension);
                        break;
                }
                case WWT_DEBUGBOX:
                        if (_settings_client.gui.newgrf_developer_tools && w->IsNewGRFInspectable()) {
                                padding = {WidgetDimensions::scaled.debugbox.Horizontal(), WidgetDimensions::scaled.debugbox.Vertical()};
                                if (NWidgetLeaf::debugbox_dimension.width == 0) {
                                        NWidgetLeaf::debugbox_dimension = GetScaledSpriteSize(SPR_WINDOW_DEBUG);
                                        NWidgetLeaf::debugbox_dimension.width += padding.width;
                                        NWidgetLeaf::debugbox_dimension.height += padding.height;
                                }
                                size = maxdim(size, NWidgetLeaf::debugbox_dimension);
                        } else {
                                /* If the setting is disabled we don't want to see it! */
                                size.width = 0;
                                fill.width = 0;
                                resize.width = 0;
                        }
                        break;

                case WWT_STICKYBOX: {
                        padding = {WidgetDimensions::scaled.stickybox.Horizontal(), WidgetDimensions::scaled.stickybox.Vertical()};
                        if (NWidgetLeaf::stickybox_dimension.width == 0) {
                                NWidgetLeaf::stickybox_dimension = maxdim(GetScaledSpriteSize(SPR_PIN_UP), GetScaledSpriteSize(SPR_PIN_DOWN));
                                NWidgetLeaf::stickybox_dimension.width += padding.width;
                                NWidgetLeaf::stickybox_dimension.height += padding.height;
                        }
                        size = maxdim(size, NWidgetLeaf::stickybox_dimension);
                        break;
                }

                case WWT_DEFSIZEBOX: {
                        padding = {WidgetDimensions::scaled.defsizebox.Horizontal(), WidgetDimensions::scaled.defsizebox.Vertical()};
                        if (NWidgetLeaf::defsizebox_dimension.width == 0) {
                                NWidgetLeaf::defsizebox_dimension = GetScaledSpriteSize(SPR_WINDOW_DEFSIZE);
                                NWidgetLeaf::defsizebox_dimension.width += padding.width;
                                NWidgetLeaf::defsizebox_dimension.height += padding.height;
                        }
                        size = maxdim(size, NWidgetLeaf::defsizebox_dimension);
                        break;
                }

                case WWT_RESIZEBOX: {
                        padding = {WidgetDimensions::scaled.resizebox.Horizontal(), WidgetDimensions::scaled.resizebox.Vertical()};
                        if (NWidgetLeaf::resizebox_dimension.width == 0) {
                                NWidgetLeaf::resizebox_dimension = maxdim(GetScaledSpriteSize(SPR_WINDOW_RESIZE_LEFT), GetScaledSpriteSize(SPR_WINDOW_RESIZE_RIGHT));
                                NWidgetLeaf::resizebox_dimension.width += padding.width;
                                NWidgetLeaf::resizebox_dimension.height += padding.height;
                        }
                        size = maxdim(size, NWidgetLeaf::resizebox_dimension);
                        break;
                }
                case WWT_EDITBOX: {
                        Dimension sprite_size = GetScaledSpriteSize(_current_text_dir == TD_RTL ? SPR_IMG_DELETE_RIGHT : SPR_IMG_DELETE_LEFT);
                        size.width = std::max(size.width, ScaleGUITrad(30) + sprite_size.width);
                        size.height = std::max(sprite_size.height, GetStringBoundingBox("_").height + WidgetDimensions::scaled.framerect.Vertical());
                }
                [[fallthrough]];
                case WWT_PUSHBTN: {
                        padding = {WidgetDimensions::scaled.frametext.Horizontal(), WidgetDimensions::scaled.framerect.Vertical()};
                        break;
                }
                case WWT_IMGBTN:
                case WWT_IMGBTN_2:
                case WWT_PUSHIMGBTN: {
                        padding = {WidgetDimensions::scaled.imgbtn.Horizontal(), WidgetDimensions::scaled.imgbtn.Vertical()};
                        Dimension d2 = GetScaledSpriteSize(this->widget_data);
                        if (this->type == WWT_IMGBTN_2) d2 = maxdim(d2, GetScaledSpriteSize(this->widget_data + 1));
                        d2.width += padding.width;
                        d2.height += padding.height;
                        size = maxdim(size, d2);
                        break;
                }
                case WWT_ARROWBTN:
                case WWT_PUSHARROWBTN: {
                        padding = {WidgetDimensions::scaled.imgbtn.Horizontal(), WidgetDimensions::scaled.imgbtn.Vertical()};
                        Dimension d2 = maxdim(GetScaledSpriteSize(SPR_ARROW_LEFT), GetScaledSpriteSize(SPR_ARROW_RIGHT));
                        d2.width += padding.width;
                        d2.height += padding.height;
                        size = maxdim(size, d2);
                        break;
                }

                case WWT_CLOSEBOX: {
                        padding = {WidgetDimensions::scaled.closebox.Horizontal(), WidgetDimensions::scaled.closebox.Vertical()};
                        if (NWidgetLeaf::closebox_dimension.width == 0) {
                                NWidgetLeaf::closebox_dimension = GetScaledSpriteSize(SPR_CLOSEBOX);
                                NWidgetLeaf::closebox_dimension.width += padding.width;
                                NWidgetLeaf::closebox_dimension.height += padding.height;
                        }
                        size = maxdim(size, NWidgetLeaf::closebox_dimension);
                        break;
                }
                case WWT_TEXTBTN:
                case WWT_PUSHTXTBTN:
                case WWT_TEXTBTN_2: {
                        padding = {WidgetDimensions::scaled.framerect.Horizontal(), WidgetDimensions::scaled.framerect.Vertical()};
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        Dimension d2 = GetStringBoundingBox(this->widget_data, this->text_size);
                        d2.width += padding.width;
                        d2.height += padding.height;
                        size = maxdim(size, d2);
                        break;
                }
                case WWT_LABEL:
                case WWT_TEXT: {
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        size = maxdim(size, GetStringBoundingBox(this->widget_data, this->text_size));
                        break;
                }
                case WWT_CAPTION: {
                        padding = {WidgetDimensions::scaled.captiontext.Horizontal(), WidgetDimensions::scaled.captiontext.Vertical()};
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        Dimension d2 = GetStringBoundingBox(this->widget_data, this->text_size);
                        d2.width += padding.width;
                        d2.height += padding.height;
                        size = maxdim(size, d2);
                        break;
                }
                case WWT_DROPDOWN:
                case NWID_BUTTON_DROPDOWN:
                case NWID_PUSHBUTTON_DROPDOWN: {
                        if (NWidgetLeaf::dropdown_dimension.width == 0) {
                                NWidgetLeaf::dropdown_dimension = GetScaledSpriteSize(SPR_ARROW_DOWN);
                                NWidgetLeaf::dropdown_dimension.width += WidgetDimensions::scaled.vscrollbar.Horizontal();
                                NWidgetLeaf::dropdown_dimension.height += WidgetDimensions::scaled.vscrollbar.Vertical();
                        }
                        padding = {WidgetDimensions::scaled.dropdowntext.Horizontal() + NWidgetLeaf::dropdown_dimension.width + WidgetDimensions::scaled.fullbevel.Horizontal(), WidgetDimensions::scaled.dropdowntext.Vertical()};
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        Dimension d2 = GetStringBoundingBox(this->widget_data, this->text_size);
                        d2.width += padding.width;
                        d2.height = std::max(d2.height + padding.height, NWidgetLeaf::dropdown_dimension.height);
                        size = maxdim(size, d2);
                        break;
                }
                default:
                        NOT_REACHED();
        }

        if (this->index >= 0) w->UpdateWidgetSize(this->index, size, padding, fill, resize);

        this->smallest_x = size.width;
        this->smallest_y = size.height;
        this->fill_x = fill.width;
        this->fill_y = fill.height;
        this->resize_x = resize.width;
        this->resize_y = resize.height;
        this->ApplyAspectRatio();
}

void NWidgetLeaf::Draw(const Window *w)
{
        if (this->current_x == 0 || this->current_y == 0) return;

        /* Setup a clipping rectangle... for WWT_EMPTY or WWT_TEXT, an extra scaled pixel is allowed in case text shadow encroaches. */
        int extra = (this->type == WWT_EMPTY || this->type == WWT_TEXT) ? ScaleGUITrad(1) : 0;
        DrawPixelInfo new_dpi;
        if (!FillDrawPixelInfo(&new_dpi, this->pos_x, this->pos_y, this->current_x + extra, this->current_y + extra)) return;
        /* ...but keep coordinates relative to the window. */
        new_dpi.left += this->pos_x;
        new_dpi.top += this->pos_y;

        AutoRestoreBackup dpi_backup(_cur_dpi, &new_dpi);

        Rect r = this->GetCurrentRect();

        bool clicked = this->IsLowered();
        switch (this->type) {
                case WWT_EMPTY:
                        /* WWT_EMPTY used as a spacer indicates a potential design issue. */
                        if (this->index == -1 && _draw_widget_outlines) {
                                GfxFillRect(r, PC_BLACK, FILLRECT_CHECKER);
                        }
                        break;

                case WWT_PUSHBTN:
                        assert(this->widget_data == 0);
                        DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, (clicked) ? FR_LOWERED : FR_NONE);
                        break;

                case WWT_IMGBTN:
                case WWT_PUSHIMGBTN:
                case WWT_IMGBTN_2:
                        DrawImageButtons(r, this->type, this->colour, clicked, this->widget_data, this->align);
                        break;

                case WWT_TEXTBTN:
                case WWT_PUSHTXTBTN:
                case WWT_TEXTBTN_2:
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        DrawFrameRect(r.left, r.top, r.right, r.bottom, this->colour, (clicked) ? FR_LOWERED : FR_NONE);
                        DrawLabel(r, this->type, clicked, this->text_colour, this->widget_data, this->align, this->text_size);
                        break;

                case WWT_ARROWBTN:
                case WWT_PUSHARROWBTN: {
                        SpriteID sprite;
                        switch (this->widget_data) {
                                case AWV_DECREASE: sprite = _current_text_dir != TD_RTL ? SPR_ARROW_LEFT : SPR_ARROW_RIGHT; break;
                                case AWV_INCREASE: sprite = _current_text_dir == TD_RTL ? SPR_ARROW_LEFT : SPR_ARROW_RIGHT; break;
                                case AWV_LEFT:     sprite = SPR_ARROW_LEFT;  break;
                                case AWV_RIGHT:    sprite = SPR_ARROW_RIGHT; break;
                                default: NOT_REACHED();
                        }
                        DrawImageButtons(r, WWT_PUSHIMGBTN, this->colour, clicked, sprite, this->align);
                        break;
                }

                case WWT_LABEL:
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        DrawLabel(r, this->type, clicked, this->text_colour, this->widget_data, this->align, this->text_size);
                        break;

                case WWT_TEXT:
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        DrawText(r, this->text_colour, this->widget_data, this->align, this->text_size);
                        break;

                case WWT_MATRIX:
                        DrawMatrix(r, this->colour, clicked, this->widget_data, this->resize_x, this->resize_y);
                        break;

                case WWT_EDITBOX: {
                        const QueryString *query = w->GetQueryString(this->index);
                        if (query != nullptr) query->DrawEditBox(w, this->index);
                        break;
                }

                case WWT_CAPTION:
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        DrawCaption(r, this->colour, w->owner, this->text_colour, this->widget_data, this->align, this->text_size);
                        break;

                case WWT_SHADEBOX:
                        assert(this->widget_data == 0);
                        DrawShadeBox(r, this->colour, w->IsShaded());
                        break;

                case WWT_DEBUGBOX:
                        DrawDebugBox(r, this->colour, clicked);
                        break;

                case WWT_STICKYBOX:
                        assert(this->widget_data == 0);
                        DrawStickyBox(r, this->colour, !!(w->flags & WF_STICKY));
                        break;

                case WWT_DEFSIZEBOX:
                        assert(this->widget_data == 0);
                        DrawDefSizeBox(r, this->colour, clicked);
                        break;

                case WWT_RESIZEBOX:
                        DrawResizeBox(r, this->colour, this->pos_x < (w->width / 2), !!(w->flags & WF_SIZING), this->widget_data == 0);
                        break;

                case WWT_CLOSEBOX:
                        DrawCloseBox(r, this->colour);
                        break;

                case WWT_DROPDOWN:
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        DrawButtonDropdown(r, this->colour, false, clicked, this->widget_data, this->align);
                        break;

                case NWID_BUTTON_DROPDOWN:
                case NWID_PUSHBUTTON_DROPDOWN:
                        if (this->index >= 0) w->SetStringParameters(this->index);
                        DrawButtonDropdown(r, this->colour, clicked, (this->disp_flags & ND_DROPDOWN_ACTIVE) != 0, this->widget_data, this->align);
                        break;

                default:
                        NOT_REACHED();
        }
        if (this->index >= 0) w->DrawWidget(r, this->index);

        if (this->IsDisabled()) {
                GfxFillRect(r.Shrink(WidgetDimensions::scaled.bevel), GetColourGradient(this->colour, SHADE_DARKER), FILLRECT_CHECKER);
        }

        DrawOutline(w, this);
}

/**
 * For a #NWID_BUTTON_DROPDOWN, test whether \a pt refers to the button or to the drop-down.
 * @param pt Point in the widget.
 * @return The point refers to the button.
 *
 * @note The magic constants are also used at #DrawButtonDropdown.
 */
bool NWidgetLeaf::ButtonHit(const Point &pt)
{
        if (_current_text_dir == TD_LTR) {
                int button_width = this->pos_x + this->current_x - NWidgetLeaf::dropdown_dimension.width;
                return pt.x < button_width;
        } else {
                int button_left = this->pos_x + NWidgetLeaf::dropdown_dimension.width;
                return pt.x >= button_left;
        }
}

/* == Conversion code from NWidgetPart array to NWidgetBase* tree == */

/**
 * Test if (an NWidgetPart) WidgetType is an attribute widget part type.
 * @param tp WidgetType to test.
 * @return True iff WidgetType is an attribute widget.
 */
static bool IsAttributeWidgetPartType(WidgetType tp)
{
        return tp > WPT_ATTRIBUTE_BEGIN && tp < WPT_ATTRIBUTE_END;
}

/**
 * Apply an attribute NWidgetPart to an NWidget.
 * @param nwid Attribute NWidgetPart
 * @param dest NWidget to apply attribute to.
 * @pre NWidgetPart must be an attribute NWidgetPart.
 */
static void ApplyNWidgetPartAttribute(const NWidgetPart &nwid, NWidgetBase *dest)
{
        switch (nwid.type) {
                case WPT_RESIZE: {
                        NWidgetResizeBase *nwrb = dynamic_cast<NWidgetResizeBase *>(dest);
                        if (nwrb == nullptr) [[unlikely]] throw std::runtime_error("WPT_RESIZE requires NWidgetResizeBase");
                        assert(nwid.u.xy.x >= 0 && nwid.u.xy.y >= 0);
                        nwrb->SetResize(nwid.u.xy.x, nwid.u.xy.y);
                        break;
                }

                case WPT_MINSIZE: {
                        NWidgetResizeBase *nwrb = dynamic_cast<NWidgetResizeBase *>(dest);
                        if (nwrb == nullptr) [[unlikely]] throw std::runtime_error("WPT_MINSIZE requires NWidgetResizeBase");
                        assert(nwid.u.xy.x >= 0 && nwid.u.xy.y >= 0);
                        nwrb->SetMinimalSize(nwid.u.xy.x, nwid.u.xy.y);
                        break;
                }

                case WPT_MINTEXTLINES: {
                        NWidgetResizeBase *nwrb = dynamic_cast<NWidgetResizeBase *>(dest);
                        if (nwrb == nullptr) [[unlikely]] throw std::runtime_error("WPT_MINTEXTLINES requires NWidgetResizeBase");
                        assert(nwid.u.text_lines.size >= FS_BEGIN && nwid.u.text_lines.size < FS_END);
                        nwrb->SetMinimalTextLines(nwid.u.text_lines.lines, nwid.u.text_lines.spacing, nwid.u.text_lines.size);
                        break;
                }

                case WPT_TEXTSTYLE: {
                        NWidgetCore *nwc = dynamic_cast<NWidgetCore *>(dest);
                        if (nwc == nullptr) [[unlikely]] throw std::runtime_error("WPT_TEXTSTYLE requires NWidgetCore");
                        nwc->SetTextStyle(nwid.u.text_style.colour, nwid.u.text_style.size);
                        break;
                }

                case WPT_ALIGNMENT: {
                        NWidgetCore *nwc = dynamic_cast<NWidgetCore *>(dest);
                        if (nwc == nullptr) [[unlikely]] throw std::runtime_error("WPT_ALIGNMENT requires NWidgetCore");
                        nwc->SetAlignment(nwid.u.align.align);
                        break;
                }

                case WPT_FILL: {
                        NWidgetResizeBase *nwrb = dynamic_cast<NWidgetResizeBase *>(dest);
                        if (nwrb == nullptr) [[unlikely]] throw std::runtime_error("WPT_FILL requires NWidgetResizeBase");
                        nwrb->SetFill(nwid.u.xy.x, nwid.u.xy.y);
                        break;
                }

                case WPT_DATATIP: {
                        NWidgetCore *nwc = dynamic_cast<NWidgetCore *>(dest);
                        if (nwc == nullptr) [[unlikely]] throw std::runtime_error("WPT_DATATIP requires NWidgetCore");
                        nwc->widget_data = nwid.u.data_tip.data;
                        nwc->tool_tip = nwid.u.data_tip.tooltip;
                        break;
                }

                case WPT_PADDING:
                        if (dest == nullptr) [[unlikely]] throw std::runtime_error("WPT_PADDING requires NWidgetBase");
                        dest->SetPadding(nwid.u.padding);
                        break;

                case WPT_PIPSPACE: {
                        NWidgetPIPContainer *nwc = dynamic_cast<NWidgetPIPContainer *>(dest);
                        if (nwc != nullptr) nwc->SetPIP(nwid.u.pip.pre, nwid.u.pip.inter, nwid.u.pip.post);

                        NWidgetBackground *nwb = dynamic_cast<NWidgetBackground *>(dest);
                        if (nwb != nullptr) nwb->SetPIP(nwid.u.pip.pre, nwid.u.pip.inter, nwid.u.pip.post);

                        if (nwc == nullptr && nwb == nullptr) [[unlikely]] throw std::runtime_error("WPT_PIPSPACE requires NWidgetPIPContainer or NWidgetBackground");
                        break;
                }

                case WPT_PIPRATIO: {
                        NWidgetPIPContainer *nwc = dynamic_cast<NWidgetPIPContainer *>(dest);
                        if (nwc != nullptr) nwc->SetPIPRatio(nwid.u.pip.pre, nwid.u.pip.inter, nwid.u.pip.post);

                        NWidgetBackground *nwb = dynamic_cast<NWidgetBackground *>(dest);
                        if (nwb != nullptr) nwb->SetPIPRatio(nwid.u.pip.pre, nwid.u.pip.inter, nwid.u.pip.post);

                        if (nwc == nullptr && nwb == nullptr) [[unlikely]] throw std::runtime_error("WPT_PIPRATIO requires NWidgetPIPContainer or NWidgetBackground");
                        break;
                }

                case WPT_SCROLLBAR: {
                        NWidgetCore *nwc = dynamic_cast<NWidgetCore *>(dest);
                        if (nwc == nullptr) [[unlikely]] throw std::runtime_error("WPT_SCROLLBAR requires NWidgetCore");
                        nwc->scrollbar_index = nwid.u.widget.index;
                        break;
                }

                case WPT_ASPECT: {
                        if (dest == nullptr) [[unlikely]] throw std::runtime_error("WPT_ASPECT requires NWidgetBase");
                        dest->aspect_ratio = nwid.u.aspect.ratio;
                        dest->aspect_flags = nwid.u.aspect.flags;
                        break;
                }

                default:
                        NOT_REACHED();
        }
}

/**
 * Make NWidget from an NWidgetPart.
 * @param nwid NWidgetPart.
 * @pre NWidgetPart must not be an attribute NWidgetPart nor WPT_ENDCONTAINER.
 * @return Pointer to created NWidget.
 */
static std::unique_ptr<NWidgetBase> MakeNWidget(const NWidgetPart &nwid)
{
        assert(!IsAttributeWidgetPartType(nwid.type));
        assert(nwid.type != WPT_ENDCONTAINER);

        switch (nwid.type) {
                case NWID_SPACER: return std::make_unique<NWidgetSpacer>(0, 0);

                case WWT_PANEL: [[fallthrough]];
                case WWT_INSET: [[fallthrough]];
                case WWT_FRAME: return std::make_unique<NWidgetBackground>(nwid.type, nwid.u.widget.colour, nwid.u.widget.index);

                case NWID_HORIZONTAL: return std::make_unique<NWidgetHorizontal>(nwid.u.cont_flags);
                case NWID_HORIZONTAL_LTR: return std::make_unique<NWidgetHorizontalLTR>(nwid.u.cont_flags);
                case NWID_VERTICAL: return std::make_unique<NWidgetVertical>(nwid.u.cont_flags);
                case NWID_SELECTION: return std::make_unique<NWidgetStacked>(nwid.u.widget.index);
                case NWID_MATRIX: return std::make_unique<NWidgetMatrix>(nwid.u.widget.colour, nwid.u.widget.index);
                case NWID_VIEWPORT: return std::make_unique<NWidgetViewport>(nwid.u.widget.index);
                case NWID_LAYER: return std::make_unique<NWidgetLayer>(nwid.u.widget.index);

                case NWID_HSCROLLBAR: [[fallthrough]];
                case NWID_VSCROLLBAR: return std::make_unique<NWidgetScrollbar>(nwid.type, nwid.u.widget.colour, nwid.u.widget.index);

                case WPT_FUNCTION: return nwid.u.func_ptr();

                default:
                        assert((nwid.type & WWT_MASK) < WWT_LAST || (nwid.type & WWT_MASK) == NWID_BUTTON_DROPDOWN);
                        return std::make_unique<NWidgetLeaf>(nwid.type, nwid.u.widget.colour, nwid.u.widget.index, 0x0, STR_NULL);
        }
}

/**
 * Construct a single nested widget in \a *dest from its parts.
 *
 * Construct a NWidgetBase object from a #NWidget function, and apply all
 * attributes that follow it, until encountering a #EndContainer, another
 * #NWidget, or the end of the parts array.
 *
 * @param nwid_begin Iterator to beginning of nested widget parts.
 * @param nwid_end Iterator to ending of nested widget parts.
 * @param[out] dest Address of pointer to use for returning the composed widget.
 * @param[out] fill_dest Fill the composed widget with child widgets.
 * @return Iterator to remaining nested widget parts.
 */
static std::span<const NWidgetPart>::iterator MakeNWidget(std::span<const NWidgetPart>::iterator nwid_begin, std::span<const NWidgetPart>::iterator nwid_end, std::unique_ptr<NWidgetBase> &dest, bool &fill_dest)
{
        dest = nullptr;

        if (IsAttributeWidgetPartType(nwid_begin->type)) [[unlikely]] throw std::runtime_error("Expected non-attribute NWidgetPart type");
        if (nwid_begin->type == WPT_ENDCONTAINER) return nwid_begin;

        fill_dest = IsContainerWidgetType(nwid_begin->type);
        dest = MakeNWidget(*nwid_begin);
        if (dest == nullptr) return nwid_begin;

        ++nwid_begin;

        /* Once a widget is created, we're now looking for attributes. */
        while (nwid_begin != nwid_end && IsAttributeWidgetPartType(nwid_begin->type)) {
                ApplyNWidgetPartAttribute(*nwid_begin, dest.get());
                ++nwid_begin;
        }

        return nwid_begin;
}

/**
 * Test if WidgetType is a container widget.
 * @param tp WidgetType to test.
 * @return True iff WidgetType is a container widget.
 */
bool IsContainerWidgetType(WidgetType tp)
{
        return tp == NWID_HORIZONTAL || tp == NWID_HORIZONTAL_LTR || tp == NWID_VERTICAL || tp == NWID_MATRIX
                || tp == WWT_PANEL || tp == WWT_FRAME || tp == WWT_INSET || tp == NWID_SELECTION || tp == NWID_LAYER;
}

/**
 * Build a nested widget tree by recursively filling containers with nested widgets read from their parts.
 * @param nwid_begin Iterator to beginning of nested widget parts.
 * @param nwid_end Iterator to ending of nested widget parts.
 * @param parent Pointer or container to use for storing the child widgets (*parent == nullptr or *parent == container or background widget).
 * @return Iterator to remaining nested widget parts.
 */
static std::span<const NWidgetPart>::iterator MakeWidgetTree(std::span<const NWidgetPart>::iterator nwid_begin, std::span<const NWidgetPart>::iterator nwid_end, std::unique_ptr<NWidgetBase> &parent)
{
        /* If *parent == nullptr, only the first widget is read and returned. Otherwise, *parent must point to either
         * a #NWidgetContainer or a #NWidgetBackground object, and parts are added as much as possible. */
        NWidgetContainer *nwid_cont = dynamic_cast<NWidgetContainer *>(parent.get());
        NWidgetBackground *nwid_parent = dynamic_cast<NWidgetBackground *>(parent.get());
        assert(parent == nullptr || (nwid_cont != nullptr && nwid_parent == nullptr) || (nwid_cont == nullptr && nwid_parent != nullptr));

        while (nwid_begin != nwid_end) {
                std::unique_ptr<NWidgetBase> sub_widget = nullptr;
                bool fill_sub = false;
                nwid_begin = MakeNWidget(nwid_begin, nwid_end, sub_widget, fill_sub);

                /* Break out of loop when end reached */
                if (sub_widget == nullptr) break;

                /* If sub-widget is a container, recursively fill that container. */
                if (fill_sub && IsContainerWidgetType(sub_widget->type)) {
                        nwid_begin = MakeWidgetTree(nwid_begin, nwid_end, sub_widget);
                }

                /* Add sub_widget to parent container if available, otherwise return the widget to the caller. */
                if (nwid_cont != nullptr) nwid_cont->Add(std::move(sub_widget));
                if (nwid_parent != nullptr) nwid_parent->Add(std::move(sub_widget));
                if (nwid_cont == nullptr && nwid_parent == nullptr) {
                        parent = std::move(sub_widget);
                        return nwid_begin;
                }
        }

        if (nwid_begin == nwid_end) return nwid_begin; // Reached the end of the array of parts?

        assert(nwid_begin < nwid_end);
        assert(nwid_begin->type == WPT_ENDCONTAINER);
        return std::next(nwid_begin); // *nwid_begin is also 'used'
}

/**
 * Construct a nested widget tree from an array of parts.
 * @param nwid_parts Span of nested widget parts.
 * @param container Container to add the nested widgets to. In case it is nullptr a vertical container is used.
 * @return Root of the nested widget tree, a vertical container containing the entire GUI.
 * @ingroup NestedWidgetParts
 */
std::unique_ptr<NWidgetBase> MakeNWidgets(std::span<const NWidgetPart> nwid_parts, std::unique_ptr<NWidgetBase> &&container)
{
        if (container == nullptr) container = std::make_unique<NWidgetVertical>();
        [[maybe_unused]] auto nwid_part = MakeWidgetTree(std::begin(nwid_parts), std::end(nwid_parts), container);
#ifdef WITH_ASSERT
        if (nwid_part != std::end(nwid_parts)) [[unlikely]] throw std::runtime_error("Did not consume all NWidgetParts");
#endif
        return std::move(container);
}

/**
 * Make a nested widget tree for a window from a parts array. Besides loading, it inserts a shading selection widget
 * between the title bar and the window body if the first widget in the parts array looks like a title bar (it is a horizontal
 * container with a caption widget) and has a shade box widget.
 * @param nwid_parts Span of nested widget parts.
 * @param[out] shade_select Pointer to the inserted shade selection widget (\c nullptr if not unserted).
 * @return Root of the nested widget tree, a vertical container containing the entire GUI.
 * @ingroup NestedWidgetParts
 */
std::unique_ptr<NWidgetBase> MakeWindowNWidgetTree(std::span<const NWidgetPart> nwid_parts, NWidgetStacked **shade_select)
{
        auto nwid_begin = std::begin(nwid_parts);
        auto nwid_end = std::end(nwid_parts);

        *shade_select = nullptr;

        /* Read the first widget recursively from the array. */
        std::unique_ptr<NWidgetBase> nwid = nullptr;
        nwid_begin = MakeWidgetTree(nwid_begin, nwid_end, nwid);
        assert(nwid != nullptr);

        NWidgetHorizontal *hor_cont = dynamic_cast<NWidgetHorizontal *>(nwid.get());

        auto root = std::make_unique<NWidgetVertical>();
        root->Add(std::move(nwid));
        if (nwid_begin == nwid_end) return root; // There is no body at all.

        if (hor_cont != nullptr && hor_cont->GetWidgetOfType(WWT_CAPTION) != nullptr && hor_cont->GetWidgetOfType(WWT_SHADEBOX) != nullptr) {
                /* If the first widget has a title bar and a shade box, silently add a shade selection widget in the tree. */
                auto shade_stack = std::make_unique<NWidgetStacked>(-1);
                *shade_select = shade_stack.get();
                /* Load the remaining parts into the shade stack. */
                shade_stack->Add(MakeNWidgets({nwid_begin, nwid_end}, std::make_unique<NWidgetVertical>()));
                root->Add(std::move(shade_stack));
                return root;
        }

        /* Load the remaining parts into 'root'. */
        return MakeNWidgets({nwid_begin, nwid_end}, std::move(root));
}

/**
 * Make a number of rows with button-like graphics, for enabling/disabling each company.
 * @param widget_first The first widget index to use.
 * @param widget_last The last widget index to use.
 * @param colour The colour in which to draw the button.
 * @param max_length Maximal number of company buttons in one row.
 * @param button_tooltip The tooltip-string of every button.
 * @param resizable Whether the rows are resizable.
 * @return Panel with rows of company buttons.
 */
std::unique_ptr<NWidgetBase> MakeCompanyButtonRows(WidgetID widget_first, WidgetID widget_last, Colours button_colour, int max_length, StringID button_tooltip, bool resizable)
{
        assert(max_length >= 1);
        std::unique_ptr<NWidgetVertical> vert = nullptr; // Storage for all rows.
        std::unique_ptr<NWidgetHorizontal> hor = nullptr; // Storage for buttons in one row.
        int hor_length = 0;

        Dimension sprite_size = GetSpriteSize(SPR_COMPANY_ICON, nullptr, ZOOM_LVL_NORMAL);
        sprite_size.width  += WidgetDimensions::unscaled.matrix.Horizontal();
        sprite_size.height += WidgetDimensions::unscaled.matrix.Vertical();

        for (WidgetID widnum = widget_first; widnum <= widget_last; widnum++) {
                /* Ensure there is room in 'hor' for another button. */
                if (hor_length == max_length) {
                        if (vert == nullptr) vert = std::make_unique<NWidgetVertical>();
                        vert->Add(std::move(hor));
                        hor = nullptr;
                        hor_length = 0;
                }
                if (hor == nullptr) {
                        hor = std::make_unique<NWidgetHorizontal>();
                        hor_length = 0;
                }

                auto panel = std::make_unique<NWidgetBackground>(WWT_PANEL, button_colour, widnum);
                panel->SetMinimalSize(sprite_size.width, sprite_size.height);
                panel->SetFill(1, 1);
                if (resizable) panel->SetResize(1, 0);
                panel->SetDataTip(0x0, button_tooltip);
                hor->Add(std::move(panel));
                hor_length++;
        }
        if (vert == nullptr) return hor; // All buttons fit in a single row.

        if (hor_length > 0 && hor_length < max_length) {
                /* Last row is partial, add a spacer at the end to force all buttons to the left. */
                auto spc = std::make_unique<NWidgetSpacer>(sprite_size.width, sprite_size.height);
                spc->SetFill(1, 1);
                if (resizable) spc->SetResize(1, 0);
                hor->Add(std::move(spc));
        }
        if (hor != nullptr) vert->Add(std::move(hor));
        return vert;
}