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/canvas_paint.h"
  11 #include "ui/gfx/size.h"
  12
  13 namespace gfx {
  14
  15 // A class designed to help with WM_PAINT operations on Windows. It will
  16 // do BeginPaint/EndPaint on init/destruction, and will create the bitmap and
  17 // canvas with the correct size and transform for the dirty rect. The bitmap
  18 // will be automatically painted to the screen on destruction.
  19 //
  20 // You MUST call isEmpty before painting to determine if anything needs
  21 // painting. Sometimes the dirty rect can actually be empty, and this makes
  22 // the bitmap functions we call unhappy. The caller should not paint in this
  23 // case.
  24 //
  25 // Therefore, all you need to do is:
  26 //   case WM_PAINT: {
  27 //     gfx::PlatformCanvasPaint canvas(hwnd);
  28 //     if (!canvas.isEmpty()) {
  29 //       ... paint to the canvas ...
  30 //     }
  31 //     return 0;
  32 //   }
  33 // Note: The created context is always inialized to (0, 0, 0, 0).
  34 class UI_EXPORT CanvasSkiaPaint : public Canvas {
  35  public:
  36   // This constructor assumes the canvas is opaque.
  37   explicit CanvasSkiaPaint(HWND hwnd) : hwnd_(hwnd), paint_dc_(NULL),
  38     for_paint_(true) {
  39     memset(&ps_, 0, sizeof(ps_));
  40     initPaint(true);
  41   }
  42
  43   CanvasSkiaPaint(HWND hwnd, bool opaque) : hwnd_(hwnd), paint_dc_(NULL),
  44       for_paint_(true) {
  45     memset(&ps_, 0, sizeof(ps_));
  46     initPaint(opaque);
  47   }
  48
  49   // Creates a CanvasSkiaPaint for the specified region that paints to the
  50   // specified dc. This does NOT do BeginPaint/EndPaint.
  51   CanvasSkiaPaint(HDC dc, bool opaque, int x, int y, int w, int h)
  52       : hwnd_(NULL),
  53         paint_dc_(dc),
  54         for_paint_(false) {
  55     memset(&ps_, 0, sizeof(ps_));
  56     ps_.rcPaint.left = x;
  57     ps_.rcPaint.right = x + w;
  58     ps_.rcPaint.top = y;
  59     ps_.rcPaint.bottom = y + h;
  60     init(opaque);
  61   }
  62
  63   virtual ~CanvasSkiaPaint() {
  64     if (!isEmpty()) {
  65       skia::PlatformCanvas* canvas = platform_canvas();
  66       canvas->restoreToCount(1);
  67       // Commit the drawing to the screen
  68       skia::DrawToNativeContext(canvas, paint_dc_, ps_.rcPaint.left,
  69                                 ps_.rcPaint.top, NULL);
  70     }
  71     if (for_paint_)
  72       EndPaint(hwnd_, &ps_);
  73   }
  74
  75   // Returns true if the invalid region is empty. The caller should call this
  76   // function to determine if anything needs painting.
  77   bool isEmpty() const {
  78     return ps_.rcPaint.right - ps_.rcPaint.left == 0 ||
  79            ps_.rcPaint.bottom - ps_.rcPaint.top == 0;
  80   }
  81
  82   // Use to access the Windows painting parameters, especially useful for
  83   // getting the bounding rect for painting: paintstruct().rcPaint
  84   const PAINTSTRUCT& paintStruct() const {
  85     return ps_;
  86   }
  87
  88   // Returns the DC that will be painted to
  89   HDC paintDC() const {
  90     return paint_dc_;
  91   }
  92
  93  protected:
  94   HWND hwnd_;
  95   HDC paint_dc_;
  96   PAINTSTRUCT ps_;
  97
  98  private:
  99   void initPaint(bool opaque) {
 100     paint_dc_ = BeginPaint(hwnd_, &ps_);
 101
 102     init(opaque);
 103   }
 104
 105   void init(bool opaque) {
 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
 113     RecreateBackingCanvas(gfx::Size(width, height), ui::SCALE_FACTOR_100P,
 114                           opaque);
 115     skia::PlatformCanvas* canvas = platform_canvas();
 116
 117     canvas->clear(SkColorSetARGB(0, 0, 0, 0));
 118
 119     // This will bring the canvas into the screen coordinate system for the
 120     // dirty rect
 121     canvas->translate(SkIntToScalar(-ps_.rcPaint.left),
 122                       SkIntToScalar(-ps_.rcPaint.top));
 123   }
 124
 125   // If true, this canvas was created for a BeginPaint.
 126   const bool for_paint_;
 127
 128   // Disallow copy and assign.
 129   CanvasSkiaPaint(const CanvasSkiaPaint&);
 130   CanvasSkiaPaint& operator=(const CanvasSkiaPaint&);
 131 };
 132
 133 }  // namespace gfx
 134
 135 #endif  // UI_GFX_CANVAS_PAINT_WIN_H_