Initialize bitmap to (0, 0, 0, 0) for CanvasPaintT<T> instances.

skia/ext/canvas_paint_win.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SKIA_EXT_CANVAS_PAINT_WIN_H_
 #define SKIA_EXT_CANVAS_PAINT_WIN_H_
 #pragma once
 
 #include "skia/ext/canvas_paint_common.h"
 #include "skia/ext/platform_canvas.h"
@@ skipping 11 matching lines @@
 // case.
 //
 // Therefore, all you need to do is:
 //   case WM_PAINT: {
 //     gfx::PlatformCanvasPaint canvas(hwnd);
 //     if (!canvas.isEmpty()) {
 //       ... paint to the canvas ...
 //     }
 //     return 0;
 //   }
+// Note: The created context is always inialized to (0, 0, 0, 0).
 template <class T>
 class CanvasPaintT : public T {
  public:
   // This constructor assumes the canvas is opaque.
   explicit CanvasPaintT(HWND hwnd) : hwnd_(hwnd), paint_dc_(NULL),
     for_paint_(true) {
     memset(&ps_, 0, sizeof(ps_));
     initPaint(true);
   }
 
@@ skipping 64 matching lines @@
     // FIXME(brettw) for ClearType, we probably want to expand the bounds of
     // painting by one pixel so that the boundaries will be correct (ClearType
     // text can depend on the adjacent pixel). Then we would paint just the
     // inset pixels to the screen.
     const int width = ps_.rcPaint.right - ps_.rcPaint.left;
     const int height = ps_.rcPaint.bottom - ps_.rcPaint.top;
     if (!canvas->initialize(width, height, opaque, NULL)) {
       // Cause a deliberate crash;
       *(char*) 0 = 0;
     }
+    canvas->clear(SkColorSetARGB(0, 0, 0, 0));
 
     // This will bring the canvas into the screen coordinate system for the
     // dirty rect
     canvas->translate(SkIntToScalar(-ps_.rcPaint.left),
                       SkIntToScalar(-ps_.rcPaint.top));
   }
 
   // If true, this canvas was created for a BeginPaint.
   const bool for_paint_;
 
   // Disallow copy and assign.
   CanvasPaintT(const CanvasPaintT&);
   CanvasPaintT& operator=(const CanvasPaintT&);
 };
 
 typedef CanvasPaintT<PlatformCanvas> PlatformCanvasPaint;
 
 }  // namespace skia
 
 #endif  // SKIA_EXT_CANVAS_PAINT_WIN_H_