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

This is a continuation of https://codereview.chromium.org/15331003/

BUG=242093
R=robertphillips@google.com, jun.a.jiang@intel.com, bsalomon@google.com

Author: bsalomon@google.com

Review URL: https://chromiumcodereview.appspot.com/15746007

git-svn-id: http://skia.googlecode.com/svn/trunk@9280 2bbb7eff-a529-9590-31e7-b0007b416f81

4 files changed, 33 insertions, 15 deletions

diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index d25709f0ea..751d869cfa 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -1280,7 +1280,8 @@ bool GrContext::readRenderTargetPixels(GrRenderTarget* target,
     // dstConfig.
     GrPixelConfig readConfig = dstConfig;
     bool swapRAndB = false;
-    if (GrPixelConfigSwapRAndB(dstConfig) == fGpu->preferredReadPixelsConfig(dstConfig)) {
+    if (GrPixelConfigSwapRAndB(dstConfig) ==
+        fGpu->preferredReadPixelsConfig(dstConfig, target->config())) {
         readConfig = GrPixelConfigSwapRAndB(readConfig);
         swapRAndB = true;
     }
@@ -1478,7 +1479,8 @@ bool GrContext::writeRenderTargetPixels(GrRenderTarget* target,
     // when drawing the scratch to the dst using a conversion effect.
     bool swapRAndB = false;
     GrPixelConfig writeConfig = srcConfig;
-    if (fGpu->preferredWritePixelsConfig(srcConfig) == GrPixelConfigSwapRAndB(srcConfig)) {
+    if (GrPixelConfigSwapRAndB(srcConfig) ==
+        fGpu->preferredWritePixelsConfig(srcConfig, target->config())) {
         writeConfig = GrPixelConfigSwapRAndB(srcConfig);
         swapRAndB = true;
     }
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index ade64312b8..5b556c5b25 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -152,11 +152,18 @@ public:
     void forceRenderTargetFlush();
 
     /**
-     * Gets a preferred 8888 config to use for writing / reading pixel data. The returned config
-     * must have at least as many bits per channel as the config param.
+     * Gets a preferred 8888 config to use for writing/reading pixel data to/from a surface with
+     * config surfaceConfig. The returned config must have at least as many bits per channel as the
+     * readConfig or writeConfig param.
      */
-    virtual GrPixelConfig preferredReadPixelsConfig(GrPixelConfig config) const { return config; }
-    virtual GrPixelConfig preferredWritePixelsConfig(GrPixelConfig config) const { return config; }
+    virtual GrPixelConfig preferredReadPixelsConfig(GrPixelConfig readConfig,
+                                                    GrPixelConfig surfaceConfig) const {
+        return readConfig;
+    }
+    virtual GrPixelConfig preferredWritePixelsConfig(GrPixelConfig writeConfig,
+                                                     GrPixelConfig surfaceConfig) const {
+        return writeConfig;
+    }
 
     /**
      * Called before uploading writing pixels to a GrTexture when the src pixel config doesn't
diff --git a/src/gpu/gl/GrGpuGL.cpp b/src/gpu/gl/GrGpuGL.cpp
index 035ef3bb1b..0c47060e4f 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;
+    } 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 {
diff --git a/src/gpu/gl/GrGpuGL.h b/src/gpu/gl/GrGpuGL.h
index 8f80a72cbc..094fca1f1b 100644
--- a/src/gpu/gl/GrGpuGL.h
+++ b/src/gpu/gl/GrGpuGL.h
@@ -44,8 +44,10 @@ public:
     bool programUnitTest(int maxStages);
 
     // GrGpu overrides
-    virtual GrPixelConfig preferredReadPixelsConfig(GrPixelConfig config) const SK_OVERRIDE;
-    virtual GrPixelConfig preferredWritePixelsConfig(GrPixelConfig config) const SK_OVERRIDE;
+    virtual GrPixelConfig preferredReadPixelsConfig(GrPixelConfig readConfig,
+                                                    GrPixelConfig surfaceConfig) const SK_OVERRIDE;
+    virtual GrPixelConfig preferredWritePixelsConfig(GrPixelConfig writeConfig,
+                                                     GrPixelConfig surfaceConfig) const SK_OVERRIDE;
     virtual bool canWriteTexturePixels(const GrTexture*, GrPixelConfig srcConfig) const SK_OVERRIDE;
     virtual bool readPixelsWillPayForYFlip(
                                     GrRenderTarget* renderTarget,