Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_linux.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_LINUX_H_
 #define SKIA_EXT_BITMAP_PLATFORM_DEVICE_LINUX_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ skipping 53 matching lines @@
  public:
   // Create a BitmapPlatformDeviceLinux from an already constructed bitmap;
   // you should probably be using Create(). This may become private later if
   // we ever have to share state between some native drawing UI and Skia, like
   // the Windows and Mac versions of this class do.
   //
   // This object takes ownership of @data.
   BitmapPlatformDevice(const SkBitmap& other, BitmapPlatformDeviceData* data);
   virtual ~BitmapPlatformDevice();
 
+  // Constructs a device with size |width| * |height|.with contents initialized

[Alexei Svitkine (slow), 2012/03/16 05:57:56]

Replace the . after |height| with a space.

[Jeff Timanus, 2012/03/16 15:52:42]

Done.

+  // to zero. |is_opaque| should be set if the caller knows the bitmap will be
+  // completely opaque and allows some optimizations.
   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque);
 
-  // This doesn't take ownership of |data|
+  // Performs the same construction as Create.
+  // Other ports require a separate construction routine because Create does not
+  // initialize the bitmap to 0.
+  static BitmapPlatformDevice* CreateAndClear(int width, int height,
+                                              bool is_opaque);
+
+  // This doesn't take ownership of |data|. If |data| is NULL, the contents

[msw, 2012/03/16 07:13:22]

is this contingent on |data|'s value? sounds like it's always cleared.

[Jeff Timanus, 2012/03/16 15:52:42]

My understanding of this code is that if |data| is non-null, then the bitmap
will have the pixel-data contents of |data|.  Otherwise, a 0-initialized bitmap
is created.

+  // of the device are initialized to 0.
   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
                                       uint8_t* data);
 
   // Overridden from SkDevice:
   virtual void setMatrixClip(const SkMatrix& transform, const SkRegion& region,
                              const SkClipStack&) OVERRIDE;
 
   // Overridden from PlatformDevice:
   virtual cairo_t* BeginPlatformPaint() OVERRIDE;
   virtual void DrawToNativeContext(PlatformSurface surface, int x, int y,
                                    const PlatformRect* src_rect) OVERRIDE;
 
  protected:
   virtual SkDevice* onCreateCompatibleDevice(SkBitmap::Config, int width,
                                              int height, bool isOpaque,
                                              Usage usage) OVERRIDE;
 
  private:
   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
                                       cairo_surface_t* surface);
 
   scoped_refptr<BitmapPlatformDeviceData> data_;
 
   DISALLOW_COPY_AND_ASSIGN(BitmapPlatformDevice);
 };
 
 }  // namespace skia
 
 #endif  // SKIA_EXT_BITMAP_PLATFORM_DEVICE_LINUX_H_