Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_win.cc

Index: skia/ext/bitmap_platform_device_win.cc
===================================================================
--- skia/ext/bitmap_platform_device_win.cc	(revision 126621)
+++ skia/ext/bitmap_platform_device_win.cc	(working copy)
@@ -87,7 +87,7 @@
 // that we can create the pixel data before calling the constructor. This is
 // required so that we can call the base class' constructor with the pixel
 // data.
-BitmapPlatformDevice* BitmapPlatformDevice::create(
+BitmapPlatformDevice* BitmapPlatformDevice::Create(
     HDC screen_dc,
     int width,
     int height,
@@ -136,8 +136,6 @@
       // obviously wrong so it will be noticable when it is not cleared
       bitmap.eraseARGB(255, 0, 255, 128);  // bright bluish green
 #endif
-    } else {
-      bitmap.eraseARGB(0, 0, 0, 0);
     }
   }
 
@@ -148,17 +146,34 @@
 }
 
 // static
-BitmapPlatformDevice* BitmapPlatformDevice::create(int width,
+BitmapPlatformDevice* BitmapPlatformDevice::Create(int width,
                                                    int height,
                                                    bool is_opaque,
                                                    HANDLE shared_section) {
   HDC screen_dc = GetDC(NULL);
-  BitmapPlatformDevice* device = BitmapPlatformDevice::create(
+  BitmapPlatformDevice* device = BitmapPlatformDevice::Create(
       screen_dc, width, height, is_opaque, shared_section);
   ReleaseDC(NULL, screen_dc);
   return device;
 }
 
+// static
+BitmapPlatformDevice* BitmapPlatformDevice::Create(int width, int height,
+                                                   bool is_opaque) {
+  return Create(width, height, is_opaque, NULL);
+}
+
+// static
+BitmapPlatformDevice* BitmapPlatformDevice::CreateAndClear(int width,
+                                                           int height,
+                                                           bool is_opaque) {
+  BitmapPlatformDevice* device = BitmapPlatformDevice::Create(width, height,
+                                                              is_opaque);
+  if (!is_opaque)
+    device->accessBitmap(true).eraseARGB(0, 0, 0, 0);
+  return device;
+}
+
 // The device will own the HBITMAP, which corresponds to also owning the pixel
 // data. Therefore, we do not transfer ownership to the SkDevice's bitmap.
 BitmapPlatformDevice::BitmapPlatformDevice(
@@ -259,7 +274,9 @@
     SkBitmap::Config config, int width, int height, bool isOpaque,
     Usage /*usage*/) {
   SkASSERT(config == SkBitmap::kARGB_8888_Config);
-  return BitmapPlatformDevice::create(width, height, isOpaque, NULL);
+  SkDevice* bitmap_device = BitmapPlatformDevice::CreateAndClear(width, height,
+                                                                 isOpaque);
+  return bitmap_device;
 }
 
 }  // namespace skia