Refactor the PlatformContext layer to have only one class.

skia/ext/platform_canvas.h

 // Copyright (c) 2006-2008 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.
 
-// Declare a platform-neutral name for this platform's canvas class
-// that can be used by upper-level classes that just need to pass a reference
-// around.
+#ifndef SKIA_EXT_PLATFORM_CANVAS_H_
+#define SKIA_EXT_PLATFORM_CANVAS_H_
 
-#if defined(WIN32)
-#include "skia/ext/platform_canvas_win.h"
-#elif defined(__APPLE__)
-#include "skia/ext/platform_canvas_mac.h"
-#elif defined(__linux__)
-#include "skia/ext/platform_canvas_linux.h"
-#endif
+// The platform-specific device will include the necessary platform headers
+// to get the surface type.
+#include "skia/ext/platform_device.h"
+#include "third_party/skia/include/core/SkCanvas.h"
 
 namespace skia {
 
+// This class is a specialization of the regular SkCanvas that is designed to
+// work with a PlatformDevice to manage platform-specific drawing. It allows
+// using both Skia operations and platform-specific operations.
+class PlatformCanvas : public SkCanvas {
+ public:
+  // Set is_opaque if you are going to erase the bitmap and not use
+  // transparency: this will enable some optimizations.
+  // If you use the version with no arguments, you MUST call initialize()
+  PlatformCanvas();
+  PlatformCanvas(int width, int height, bool is_opaque);
+  virtual ~PlatformCanvas();
+
 #if defined(WIN32)
-typedef PlatformCanvasWin PlatformCanvas;
+  // Windows ------------------------------------------------------------------
+
+  // The shared_section parameter is passed to gfx::PlatformDevice::create.
+  // See it for details.
+  PlatformCanvas(int width, int height, bool is_opaque, HANDLE shared_section);
+
+  // For two-part init, call if you use the no-argument constructor above. Note
+  // that we want this to optionally match the Linux initialize if you only
+  // pass 3 arguments, hence the evil default argument.
+  bool initialize(int width, int height, bool is_opaque,
+                  HANDLE shared_section = NULL);
+
 #elif defined(__APPLE__)
-typedef PlatformCanvasMac PlatformCanvas;
+  // Mac -----------------------------------------------------------------------
+
+  PlatformCanvas(int width, int height, bool is_opaque,
+                 CGContextRef context);
+  PlatformCanvas(int width, int height, bool is_opaque, uint8_t* context);
+
+  // For two-part init, call if you use the no-argument constructor above
+  bool initialize(int width, int height, bool is_opaque, uint8_t* data = NULL);
+
 #elif defined(__linux__)
-typedef PlatformCanvasLinux PlatformCanvas;
+  // Linux ---------------------------------------------------------------------
+
+  // Construct a canvas from the given memory region. The memory is not cleared
+  // first. @data must be, at least, @height * StrideForWidth(@width) bytes.
+  PlatformCanvas(int width, int height, bool is_opaque, uint8_t* data);
+
+  // For two-part init, call if you use the no-argument constructor above
+  bool initialize(int width, int height, bool is_opaque, uint8_t* data = NULL);
+
 #endif
+  // Shared --------------------------------------------------------------------
+
+  // These calls should surround calls to platform drawing routines, the
+  // surface returned here can be used with the native platform routines
+  //
+  // Call endPlatformPaint when you are done and want to use Skia operations
+  // after calling the platform-specific beginPlatformPaint; this will
+  // synchronize the bitmap to OS if necessary.
+  PlatformDevice::PlatformSurface beginPlatformPaint();
+  void endPlatformPaint();
+
+  // Returns the platform device pointer of the topmost rect with a non-empty
+  // clip. In practice, this is usually either the top layer or nothing, since
+  // we usually set the clip to new layers when we make them.
+  //
+  // If there is no layer that is not all clipped out, this will return a
+  // dummy device so callers do not have to check. If you are concerned about
+  // performance, check the clip before doing any painting.
+  //
+  // This is different than SkCanvas' getDevice, because that returns the
+  // bottommost device.
+  //
+  // Danger: the resulting device should not be saved. It will be invalidated
+  // by the next call to save() or restore().
+  PlatformDevice& getTopPlatformDevice() const;
+
+  // Return the stride (length of a line in bytes) for the given width. Because
+  // we use 32-bits per pixel, this will be roughly 4*width. However, for
+  // alignment reasons we may wish to increase that.
+  static size_t StrideForWidth(unsigned width);
+
+  // Allow callers to see the non-virtual function even though we have an
+  // override of a virtual one.
+  // FIXME(brettw) is this necessary?
+  using SkCanvas::clipRect;
+
+ protected:
+  // Creates a device store for use by the canvas. We override this so that
+  // the device is always our own so we know that we can use platform
+  // operations on it.
+  virtual SkDevice* createDevice(SkBitmap::Config,
+                                 int width,
+                                 int height,
+                                 bool is_opaque,
+                                 bool isForLayer);
+
+ private:
+  // Unimplemented. This is to try to prevent people from calling this function
+  // on SkCanvas. SkCanvas' version is not virtual, so we can't prevent this
+  // 100%, but hopefully this will make people notice and not use the function.
+  // Calling SkCanvas' version will create a new device which is not compatible
+  // with us and we will crash if somebody tries to draw into it with
+  // CoreGraphics.
+  virtual SkDevice* setBitmapDevice(const SkBitmap& bitmap);
+
+  // Disallow copy and assign.
+  PlatformCanvas(const PlatformCanvas&);
+  PlatformCanvas& operator=(const PlatformCanvas&);
+};
 
 }  // namespace skia
+
+#endif  // SKIA_EXT_PLATFORM_CANVAS_H_