fix slowness of getImageData() for CanvasRenderingContext2D in linux due to un-optimized format for…

src/gpu/gl/GrGpuGL.cpp

Index: src/gpu/gl/GrGpuGL.cpp
diff --git a/src/gpu/gl/GrGpuGL.cpp b/src/gpu/gl/GrGpuGL.cpp
index 035ef3bb1bf43c99d5d80552cf16c1bc317d959c..e9f61dcd74d71bf31b584995c8567994832bf11c 100644
--- a/src/gpu/gl/GrGpuGL.cpp
+++ b/src/gpu/gl/GrGpuGL.cpp
@@ -266,21 +266,28 @@ void GrGpuGL::fillInConfigRenderableTable() {
 }
 
 namespace {
-GrPixelConfig preferred_pixel_ops_config(GrPixelConfig config) {
-    if (GR_GL_RGBA_8888_PIXEL_OPS_SLOW && kRGBA_8888_GrPixelConfig == config) {
+GrPixelConfig preferred_pixel_ops_config(GrPixelConfig cpuConfig, GrPixelConfig surfaceConfig) {
+    if (GR_GL_RGBA_8888_PIXEL_OPS_SLOW && kRGBA_8888_GrPixelConfig == cpuConfig) {
         return kBGRA_8888_GrPixelConfig;

[robertphillips, 2013/05/22 15:33:24]

seems like there is an extra set of parens in here

+    } else if ((GrBytesPerPixel(cpuConfig) == 4 &&
+                GrPixelConfigSwapRAndB(cpuConfig) == surfaceConfig)) {
+        // It is believed to be slower (at least on Intel Linux GL drivers) to readback BGRA from

[Jun Jiang, 2013/05/22 17:27:20]

I think it may be more reasonable to say "it is believed to be slower on Mesa 3D
graphics library in Linux" instead of "Intel Linux GL drivers". The decision to
make it fall back to slow path is in Mesa library(src/mesa/main/readpix.c). 

+        // an RGBA surface and vice-versa. Perhaps this should be keyed off the GL vendor string.
+        return surfaceConfig;
     } else {
-        return config;
+        return cpuConfig;
     }
 }
 }
 
-GrPixelConfig GrGpuGL::preferredReadPixelsConfig(GrPixelConfig config) const {
-    return preferred_pixel_ops_config(config);
+GrPixelConfig GrGpuGL::preferredReadPixelsConfig(GrPixelConfig readConfig,
+                                                 GrPixelConfig surfaceConfig) const {
+    return preferred_pixel_ops_config(readConfig, surfaceConfig);
 }
 
-GrPixelConfig GrGpuGL::preferredWritePixelsConfig(GrPixelConfig config) const {
-    return preferred_pixel_ops_config(config);
+GrPixelConfig GrGpuGL::preferredWritePixelsConfig(GrPixelConfig writeConfig,
+                                                  GrPixelConfig surfaceConfig) const {
+    return preferred_pixel_ops_config(writeConfig, surfaceConfig);
 }
 
 bool GrGpuGL::canWriteTexturePixels(const GrTexture* texture, GrPixelConfig srcConfig) const {