Convert format of pixels read from GL to BGRA on CPU if necessary

ReadPixels with format GL_BGRA_EXT is not necessarily supported by the
GLES2-based GPU command buffer. The support for this format needs to be
explicitly queried, and if it is not supported, the pixels need to be
converted from RGBA to BGRA on the CPU if a BGRA result is desired.

BUG=380129
TEST=WebGL conformance tests

Review URL: https://codereview.chromium.org/316553002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274847 0039d316-1c4b-4281-b951-d872f2087c98

content/renderer/media/renderer_gpu_video_accelerator_factories.cc

@@ -200,12 +200,22 @@ void RendererGpuVideoAcceleratorFactories::ReadPixels(
   gles2->FramebufferTexture2D(
       GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tmp_texture, 0);
   gles2->PixelStorei(GL_PACK_ALIGNMENT, 4);
+
 #if SK_B32_SHIFT == 0 && SK_G32_SHIFT == 8 && SK_R32_SHIFT == 16 && \
     SK_A32_SHIFT == 24
   GLenum skia_format = GL_BGRA_EXT;
+  GLenum read_format = GL_BGRA_EXT;
+  GLint supported_format = 0;
+  GLint supported_type = 0;
+  gles2->GetIntegerv(GL_IMPLEMENTATION_COLOR_READ_FORMAT, &supported_format);
+  gles2->GetIntegerv(GL_IMPLEMENTATION_COLOR_READ_TYPE, &supported_type);
+  if (supported_format != GL_BGRA_EXT || supported_type != GL_UNSIGNED_BYTE) {
+    read_format = GL_RGBA;
+  }
 #elif SK_R32_SHIFT == 0 && SK_G32_SHIFT == 8 && SK_B32_SHIFT == 16 && \
     SK_A32_SHIFT == 24
   GLenum skia_format = GL_RGBA;
+  GLenum read_format = GL_RGBA;
 #else
 #error Unexpected Skia ARGB_8888 layout!
 #endif
@@ -213,11 +223,28 @@ void RendererGpuVideoAcceleratorFactories::ReadPixels(
                     visible_rect.y(),
                     visible_rect.width(),
                     visible_rect.height(),
-                    skia_format,
+                    read_format,
                     GL_UNSIGNED_BYTE,
                     pixels.pixelRef()->pixels());
   gles2->DeleteFramebuffers(1, &fb);
   gles2->DeleteTextures(1, &tmp_texture);
+
+  if (skia_format != read_format) {
+    DCHECK(read_format == GL_RGBA);
+    int pixel_count = visible_rect.width() * visible_rect.height();
+    uint32_t* pixels_ptr = static_cast<uint32_t*>(pixels.pixelRef()->pixels());
+    for (int i = 0; i < pixel_count; ++i) {
+        uint32_t r = pixels_ptr[i] & 0xFF;
+        uint32_t g = (pixels_ptr[i] >> 8) & 0xFF;
+        uint32_t b = (pixels_ptr[i] >> 16) & 0xFF;
+        uint32_t a = (pixels_ptr[i] >> 24) & 0xFF;
+        pixels_ptr[i] = (r << SK_R32_SHIFT) |
+                        (g << SK_G32_SHIFT) |
+                        (b << SK_B32_SHIFT) |
+                        (a << SK_A32_SHIFT);
+    }
+  }
+
   DCHECK_EQ(gles2->GetError(), static_cast<GLenum>(GL_NO_ERROR));
 }