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

src/gpu/gl/GrGpuGL.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGpuGL.h"
 #include "GrGLStencilBuffer.h"
@@ skipping 248 matching lines @@
     if (this->glCaps().rgba8RenderbufferSupport()) {
         fConfigRenderSupport[kRGBA_8888_GrPixelConfig] = true;
     }
 
     if (this->glCaps().bgraFormatSupport()) {
         fConfigRenderSupport[kBGRA_8888_GrPixelConfig] = true;
     }
 }
 
 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;
+    } else if (GrBytesPerPixel(cpuConfig) == 4 &&
+                GrPixelConfigSwapRAndB(cpuConfig) == surfaceConfig) {
+        // Mesa 3D takes a slow path on when reading back  BGRA from an RGBA surface and vice-versa.
+        // Perhaps this should be guarded by some compiletime or runtime check.
+        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 {
     if (kIndex_8_GrPixelConfig == srcConfig || kIndex_8_GrPixelConfig == texture->config()) {
         return false;
     }
     if (srcConfig != texture->config() && kES2_GrGLBinding == this->glBinding()) {
         // In general ES2 requires the internal format of the texture and the format of the src
         // pixels to match. However, It may or may not be possible to upload BGRA data to a RGBA
         // texture. It depends upon which extension added BGRA. The Apple extension allows it
@@ skipping 2209 matching lines @@
             this->setVertexArrayID(gpu, 0);
         }
         int attrCount = gpu->glCaps().maxVertexAttributes();
         if (fDefaultVertexArrayAttribState.count() != attrCount) {
             fDefaultVertexArrayAttribState.resize(attrCount);
         }
         attribState = &fDefaultVertexArrayAttribState;
     }
     return attribState;
 }