skia/ext/canvas_paint_win.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef SKIA_EXT_CANVAS_PAINT_WIN_H_
   6 #define SKIA_EXT_CANVAS_PAINT_WIN_H_
   7 #pragma once
   8
   9 #include "skia/ext/canvas_paint_common.h"
  10 #include "skia/ext/platform_canvas.h"
  11
  12 namespace skia {
  13
  14 // A class designed to help with WM_PAINT operations on Windows. It will
  15 // do BeginPaint/EndPaint on init/destruction, and will create the bitmap and
  16 // canvas with the correct size and transform for the dirty rect. The bitmap
  17 // will be automatically painted to the screen on destruction.
  18 //
  19 // You MUST call isEmpty before painting to determine if anything needs
  20 // painting. Sometimes the dirty rect can actually be empty, and this makes
  21 // the bitmap functions we call unhappy. The caller should not paint in this
  22 // case.
  23 //
  24 // Therefore, all you need to do is:
  25 //   case WM_PAINT: {
  26 //     gfx::PlatformCanvasPaint canvas(hwnd);
  27 //     if (!canvas.isEmpty()) {
  28 //       ... paint to the canvas ...
  29 //     }
  30 //     return 0;
  31 //   }
  32 template <class T>
  33 class CanvasPaintT : public T {
  34  public:
  35   // This constructor assumes the canvas is opaque.
  36   explicit CanvasPaintT(HWND hwnd) : hwnd_(hwnd), paint_dc_(NULL),
  37     for_paint_(true) {
  38     memset(&ps_, 0, sizeof(ps_));
  39     initPaint(true);
  40   }
  41
  42   CanvasPaintT(HWND hwnd, bool opaque) : hwnd_(hwnd), paint_dc_(NULL),
  43       for_paint_(true) {
  44     memset(&ps_, 0, sizeof(ps_));
  45     initPaint(opaque);
  46   }
  47
  48   // Creates a CanvasPaintT for the specified region that paints to the
  49   // specified dc. This does NOT do BeginPaint/EndPaint.
  50   CanvasPaintT(HDC dc, bool opaque, int x, int y, int w, int h)
  51       : hwnd_(NULL),
  52         paint_dc_(dc),
  53         for_paint_(false) {
  54     memset(&ps_, 0, sizeof(ps_));
  55     ps_.rcPaint.left = x;
  56     ps_.rcPaint.right = x + w;
  57     ps_.rcPaint.top = y;
  58     ps_.rcPaint.bottom = y + h;
  59     init(opaque);
  60   }
  61
  62   virtual ~CanvasPaintT() {
  63     if (!isEmpty()) {
  64       PlatformCanvas* canvas = GetPlatformCanvas(this);
  65       canvas->restoreToCount(1);
  66       // Commit the drawing to the screen
  67       skia::DrawToNativeContext(canvas, paint_dc_, ps_.rcPaint.left,
  68                                 ps_.rcPaint.top, NULL);
  69     }
  70     if (for_paint_)
  71       EndPaint(hwnd_, &ps_);
  72   }
  73
  74   // Returns true if the invalid region is empty. The caller should call this
  75   // function to determine if anything needs painting.
  76   bool isEmpty() const {
  77     return ps_.rcPaint.right - ps_.rcPaint.left == 0 ||
  78            ps_.rcPaint.bottom - ps_.rcPaint.top == 0;
  79   }
  80
  81   // Use to access the Windows painting parameters, especially useful for
  82   // getting the bounding rect for painting: paintstruct().rcPaint
  83   const PAINTSTRUCT& paintStruct() const {
  84     return ps_;
  85   }
  86
  87   // Returns the DC that will be painted to
  88   HDC paintDC() const {
  89     return paint_dc_;
  90   }
  91
  92  protected:
  93   HWND hwnd_;
  94   HDC paint_dc_;
  95   PAINTSTRUCT ps_;
  96
  97  private:
  98   void initPaint(bool opaque) {
  99     paint_dc_ = BeginPaint(hwnd_, &ps_);
 100
 101     init(opaque);
 102   }
 103
 104   void init(bool opaque) {
 105     PlatformCanvas* canvas = GetPlatformCanvas(this);
 106     // FIXME(brettw) for ClearType, we probably want to expand the bounds of
 107     // painting by one pixel so that the boundaries will be correct (ClearType
 108     // text can depend on the adjacent pixel). Then we would paint just the
 109     // inset pixels to the screen.
 110     const int width = ps_.rcPaint.right - ps_.rcPaint.left;
 111     const int height = ps_.rcPaint.bottom - ps_.rcPaint.top;
 112     if (!canvas->initialize(width, height, opaque, NULL)) {
 113       // Cause a deliberate crash;
 114       *(char*) 0 = 0;
 115     }
 116
 117     // This will bring the canvas into the screen coordinate system for the
 118     // dirty rect
 119     canvas->translate(SkIntToScalar(-ps_.rcPaint.left),
 120                       SkIntToScalar(-ps_.rcPaint.top));
 121   }
 122
 123   // If true, this canvas was created for a BeginPaint.
 124   const bool for_paint_;
 125
 126   // Disallow copy and assign.
 127   CanvasPaintT(const CanvasPaintT&);
 128   CanvasPaintT& operator=(const CanvasPaintT&);
 129 };
 130
 131 typedef CanvasPaintT<PlatformCanvas> PlatformCanvasPaint;
 132
 133 }  // namespace skia
 134
 135 #endif  // SKIA_EXT_CANVAS_PAINT_WIN_H_