ui/gfx/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 UI_GFX_CANVAS_PAINT_WIN_H_
   6 #define UI_GFX_CANVAS_PAINT_WIN_H_
   7
   8 #include "skia/ext/platform_canvas.h"
   9 #include "ui/gfx/canvas.h"
  10 #include "ui/gfx/geometry/size.h"
  11 #include "ui/gfx/win/dpi.h"
  12
  13 namespace gfx {
  14
  15 // A class designed to help with WM_PAINT operations on Windows. It will create
  16 // the bitmap and canvas with the correct size and transform for the dirty rect.
  17 // The bitmap 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 //     PAINTSTRUCT ps;
  27 //     HDC hdc = BeginPaint(hwnd, &ps);
  28 //     gfx::CanvasSkiaPaint canvas(hwnd, hdc, ps);
  29 //     if (!canvas.isEmpty()) {
  30 //       ... paint to the canvas ...
  31 //     }
  32 //     EndPaint(hwnd, &ps);
  33 //     return 0;
  34 //   }
  35 // Note: The created context is always inialized to (0, 0, 0, 0).
  36 class GFX_EXPORT CanvasSkiaPaint : public Canvas {
  37  public:
  38   // This constructor assumes the canvas is opaque.
  39   CanvasSkiaPaint(HWND hwnd, HDC dc, const PAINTSTRUCT& ps);
  40   virtual ~CanvasSkiaPaint();
  41
  42   // Creates a CanvasSkiaPaint for the specified region that paints to the
  43   // specified dc.
  44   CanvasSkiaPaint(HDC dc, bool opaque, int x, int y, int w, int h);
  45
  46   // Returns the rectangle that is invalid.
  47   virtual gfx::Rect GetInvalidRect() const;
  48
  49   // Returns true if the invalid region is empty. The caller should call this
  50   // function to determine if anything needs painting.
  51   bool is_empty() const {
  52     return ps_.rcPaint.right - ps_.rcPaint.left == 0 ||
  53            ps_.rcPaint.bottom - ps_.rcPaint.top == 0;
  54   };
  55
  56   // Use to access the Windows painting parameters, especially useful for
  57   // getting the bounding rect for painting: paintstruct().rcPaint
  58   const PAINTSTRUCT& paint_struct() const { return ps_; }
  59
  60   // Returns the DC that will be painted to
  61   HDC paint_dc() const { return paint_dc_; }
  62
  63  private:
  64   void Init(bool opaque);
  65
  66   HWND hwnd_;
  67   HDC paint_dc_;
  68   PAINTSTRUCT ps_;
  69
  70   // Disallow copy and assign.
  71   DISALLOW_COPY_AND_ASSIGN(CanvasSkiaPaint);
  72 };
  73
  74 }  // namespace gfx
  75
  76 #endif  // UI_GFX_CANVAS_PAINT_WIN_H_