Switch from using GdkPixbuf to cairo for painting on Drawables.

Make everything use ARGB order in registers (B.G.R.A order in memory on
little-endian systems)

Review URL: http://codereview.chromium.org/8227


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@4845 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 58 insertions, 34 deletions

diff --git a/base/gfx/bitmap_platform_device_linux.cc b/base/gfx/bitmap_platform_device_linux.cc
index f86323e..c80a273 100644
--- a/base/gfx/bitmap_platform_device_linux.cc
+++ b/base/gfx/bitmap_platform_device_linux.cc
@@ -4,8 +4,7 @@
 
 #include "base/gfx/bitmap_platform_device_linux.h"
 
-#include <gdk/gdk.h>
-#include <gdk-pixbuf/gdk-pixbuf.h>
+#include <cairo/cairo.h>
 
 #include "base/logging.h"
 
@@ -17,21 +16,14 @@ namespace gfx {
 // data.
 BitmapPlatformDeviceLinux* BitmapPlatformDeviceLinux::Create(
     int width, int height, bool is_opaque) {
-  GdkPixbuf* pixbuf = gdk_pixbuf_new(GDK_COLORSPACE_RGB, true, 8, width, height);
-  if (!pixbuf)
-    return NULL;
-
-  DCHECK_EQ(gdk_pixbuf_get_colorspace(pixbuf), GDK_COLORSPACE_RGB);
-  DCHECK_EQ(gdk_pixbuf_get_bits_per_sample(pixbuf), 8);
-  DCHECK(gdk_pixbuf_get_has_alpha(pixbuf));
-  DCHECK_EQ(gdk_pixbuf_get_n_channels(pixbuf), 4);
-  DCHECK_EQ(gdk_pixbuf_get_width(pixbuf), width);
-  DCHECK_EQ(gdk_pixbuf_get_height(pixbuf), height);
+  cairo_surface_t* surface =
+      cairo_image_surface_create(CAIRO_FORMAT_ARGB32,
+                                 width, height);
 
   SkBitmap bitmap;
   bitmap.setConfig(SkBitmap::kARGB_8888_Config, width, height,
-                   gdk_pixbuf_get_rowstride(pixbuf));
-  bitmap.setPixels(gdk_pixbuf_get_pixels(pixbuf));
+                   cairo_image_surface_get_stride(surface));
+  bitmap.setPixels(cairo_image_surface_get_data(surface));
   bitmap.setIsOpaque(is_opaque);
 
 #ifndef NDEBUG
@@ -41,15 +33,15 @@ BitmapPlatformDeviceLinux* BitmapPlatformDeviceLinux::Create(
 #endif
 
   // The device object will take ownership of the graphics context.
-  return new BitmapPlatformDeviceLinux(bitmap, pixbuf);
+  return new BitmapPlatformDeviceLinux(bitmap, surface);
 }
 
 // The device will own the bitmap, which corresponds to also owning the pixel
 // data. Therefore, we do not transfer ownership to the SkDevice's bitmap.
 BitmapPlatformDeviceLinux::BitmapPlatformDeviceLinux(const SkBitmap& bitmap,
-                                                     GdkPixbuf* pixbuf)
+                                                     cairo_surface_t* surface)
     : PlatformDeviceLinux(bitmap),
-      pixbuf_(pixbuf) {
+      surface_(surface) {
 }
 
 BitmapPlatformDeviceLinux::BitmapPlatformDeviceLinux(
@@ -59,9 +51,9 @@ BitmapPlatformDeviceLinux::BitmapPlatformDeviceLinux(
 }
 
 BitmapPlatformDeviceLinux::~BitmapPlatformDeviceLinux() {
-  if (pixbuf_) {
-    g_object_unref(pixbuf_);
-    pixbuf_ = NULL;
+  if (surface_) {
+    cairo_surface_destroy(surface_);
+    surface_ = NULL;
   }
 }
 
diff --git a/base/gfx/bitmap_platform_device_linux.h b/base/gfx/bitmap_platform_device_linux.h
index 99ca534..c029293 100644
--- a/base/gfx/bitmap_platform_device_linux.h
+++ b/base/gfx/bitmap_platform_device_linux.h
@@ -8,21 +8,51 @@
 #include "base/gfx/platform_device_linux.h"
 #include "base/ref_counted.h"
 
-#include <gdk-pixbuf/gdk-pixbuf.h>
+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:
@@ -30,11 +60,13 @@ class BitmapPlatformDeviceLinux : public PlatformDeviceLinux {
   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.
@@ -43,10 +75,10 @@ class BitmapPlatformDeviceLinux : public PlatformDeviceLinux {
   // 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