Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_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_BITMAP_PLATFORM_DEVICE_WIN_H_
 #define SKIA_EXT_BITMAP_PLATFORM_DEVICE_WIN_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ skipping 14 matching lines @@
 // another bitmap to this device's bitmap and everything will work properly.
 // For us, that other bitmap will become invalid as soon as the device becomes
 // invalid, which may lead to subtle bugs. Therefore, DO NOT ASSIGN THE
 // DEVICE'S PIXEL DATA TO ANOTHER BITMAP, make sure you copy instead.
 class SK_API BitmapPlatformDevice : public PlatformDevice, public SkDevice {
  public:
   // Factory function. The screen DC is used to create the bitmap, and will not
   // be stored beyond this function. is_opaque should be set if the caller
   // knows the bitmap will be completely opaque and allows some optimizations.
   //
-  // The shared_section parameter is optional (pass NULL for default behavior).
-  // If shared_section is non-null, then it must be a handle to a file-mapping
-  // object returned by CreateFileMapping.  See CreateDIBSection for details.
-  static BitmapPlatformDevice* create(HDC screen_dc, int width, int height,
+  // The |shared_section| parameter is optional (pass NULL for default
+  // behavior). If |shared_section| is non-null, then it must be a handle to a
+  // file-mapping object returned by CreateFileMapping.  See CreateDIBSection
+  // for details. If |shared_section| is null, the bitmap backing store is not
+  // initialized.
+  static BitmapPlatformDevice* Create(HDC screen_dc, int width, int height,
                                       bool is_opaque, HANDLE shared_section);
 
   // This version is the same as above but will get the screen DC itself.
-  static BitmapPlatformDevice* create(int width, int height, bool is_opaque,
+  static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
                                       HANDLE shared_section);
 
+  // Create a BitmapPlatformDevice with no shared section. The bitmap is not
+  // initialized to 0.
+  static BitmapPlatformDevice* Create(int width, int height, bool is_opaque);
+
+  // Creates a BitmapPlatformDevice instance respecting the parameters as above.
+  // If |is_opaque| is false, then the bitmap is initialzed to 0.
+  static BitmapPlatformDevice* CreateAndClear(int width, int height,
+                                              bool is_opaque);
+
   virtual ~BitmapPlatformDevice();
 
   // PlatformDevice overrides
   // Retrieves the bitmap DC, which is the memory DC for our bitmap data. The
   // bitmap DC is lazy created.
   virtual PlatformSurface BeginPlatformPaint() OVERRIDE;
   virtual void EndPlatformPaint() OVERRIDE;
 
   virtual void DrawToNativeContext(HDC dc, int x, int y,
                                    const RECT* src_rect) OVERRIDE;
@@ skipping 30 matching lines @@
 #ifdef SK_DEBUG
   int begin_paint_count_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(BitmapPlatformDevice);
 };
 
 }  // namespace skia
 
 #endif  // SKIA_EXT_BITMAP_PLATFORM_DEVICE_WIN_H_