Switch from using GdkPixbuf to cairo for painting on Drawables.

base/gfx/bitmap_platform_device_linux.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.
 
 #ifndef BASE_GFX_BITMAP_PLATFORM_DEVICE_LINUX_H_
 #define BASE_GFX_BITMAP_PLATFORM_DEVICE_LINUX_H_
 
 #include "base/gfx/platform_device_linux.h"
 #include "base/ref_counted.h"
 
-#include <gdk-pixbuf/gdk-pixbuf.h>
+struct _cairo_surface;

[Evan Martin, 2008/11/05 23:52:23]

this isn't necessary when you have the following line

+typedef struct _cairo_surface cairo_surface_t;
+
+// -----------------------------------------------------------------------------
+// Image byte ordering on Linux:
+//
+// Pixels are packed into 32-bit words these days. Even for 24-bit images,
+// often 8-bits will be left unused for alignment reasons. Thus, when you see
+// ARGB as the byte order you have to wonder if that's in memory order or
+// little-endian order. Here I'll write A.R.G.B to specifiy the memory order.
+//
+// GdkPixbuf's provide a nice backing store and defaults to R.G.B.A order.
+// They'll do the needed byte swapping to match the X server when drawn.
+//
+// Skia can be controled in skia/include/corecg/SkUserConfig.h (see bits about
+// SK_R32_SHIFT). For Linux we define it to be ARGB in registers. For little
+// endian machines that means B.G.R.A in memory.
+//
+// The image loaders are controlled in
+// webkit/port/platform/image-decoders/ImageDecoder.h (see setRGBA). These are
+// also configured for ARGB in registers.
+//
+// Cairo's only 32-bit mode is ARGB in registers.
+//
+// X servers commonly have a 32-bit visual with xRGB in registers (since they
+// typically don't do alpha blending of drawables at the user level. Composite
+// extensions aside.)
+//
+// We don't use GdkPixbuf because its byte order differs from the rest. Most
+// importantly, it differs from Cairo which, being a system library, is
+// something that we can't easily change.
+// -----------------------------------------------------------------------------
 
 namespace gfx {
 
 // -----------------------------------------------------------------------------
-// This is the Linux bitmap backing for Skia. It's a GdkPixbuf of the correct
-// size and we implement a SkPixelRef in order that Skia can write directly to
-// the pixel memory backing the Pixbuf.
+// This is the Linux bitmap backing for Skia. We create a Cairo image surface
+// to store the backing buffer. This buffer is BGRA in memory (on little-endian
+// machines).
 //
-// We then provide an accessor for getting the pixbuf object and that can be
-// drawn to a GDK drawing area to display the rendering result.
+// For now we are also using Cairo to paint to the Drawables so we provide an
+// accessor for getting the surface.
 //
 // This is all quite ok for test_shell. In the future we will want to use
 // shared memory between the renderer and the main process at least. In this
-// case we'll probably create the pixbuf from a precreated region of memory.
+// case we'll probably create the buffer from a precreated region of memory.
 // -----------------------------------------------------------------------------
 class BitmapPlatformDeviceLinux : public PlatformDeviceLinux {
  public:
   /// Static constructor. I don't understand this, it's just a copy of the mac
   static BitmapPlatformDeviceLinux* Create(int width, int height,
                                            bool is_opaque);
 
-  /// 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.
-  BitmapPlatformDeviceLinux(const SkBitmap& other, GdkPixbuf* pixbuf);
+  // 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 @surface.
+  BitmapPlatformDeviceLinux(const SkBitmap& other, cairo_surface_t* surface);
   virtual ~BitmapPlatformDeviceLinux();
 
   // A stub copy constructor.  Needs to be properly implemented.
   BitmapPlatformDeviceLinux(const BitmapPlatformDeviceLinux& other);
 
   // Bitmaps aren't vector graphics.
   virtual bool IsVectorial() { return false; }
 
-  GdkPixbuf* pixbuf() const { return pixbuf_; }
+  cairo_surface_t* surface() const { return surface_; }
 
  private:
-  GdkPixbuf* pixbuf_;
+  cairo_surface_t* surface_;
 };
 
 }  // namespace gfx
 
 #endif  // BASE_GFX_BITMAP_PLATFORM_DEVICE_LINUX_H_