Expose GpuMemoryBufferId through glGetImageivCHROMIUM.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 916 matching lines @@
     m_gl->TexImage2D(target, level, internalformat, width, height, border, format, type, 0);
 }
 
 void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
 {
     if (info->imageId) {
         m_gl->BindTexture(info->parameters.target, info->textureId);
         m_gl->ReleaseTexImage2DCHROMIUM(info->parameters.target, info->imageId);
         m_gl->DestroyImageCHROMIUM(info->imageId);
         info->imageId = 0;
+        info->gpuMemoryBufferId = -1;
     }
 }
 
 void DrawingBuffer::clearChromiumImageAlpha(const TextureInfo& info)
 {
     if (m_wantAlphaChannel)
         return;
     if (!contextProvider()->getCapabilities().chromium_image_rgb_emulation)
         return;
 
@@ skipping 18 matching lines @@
 
     // First, try to allocate a CHROMIUM_image. This always has the potential to
     // fail.
     TextureParameters parameters = chromiumImageTextureParameters();
     GLuint imageId = m_gl->CreateGpuMemoryBufferImageCHROMIUM(size.width(), size.height(), parameters.creationInternalColorFormat, GC3D_SCANOUT_CHROMIUM);
     if (!imageId)
         return createDefaultTextureAndAllocateMemory(size);
 
     GLuint textureId = createColorTexture(parameters);
     m_gl->BindTexImage2DCHROMIUM(parameters.target, imageId);
+    GLint gpuMemoryBufferId = -1;
+    m_gl->GetImageivCHROMIUM(imageId, GC3D_GPU_MEMORY_BUFFER_ID, &gpuMemoryBufferId);

[Ken Russell (switch to Gerrit), 2016/05/27 01:02:10]

Questions:

1. Does glGetImageivCHROMIUM require a round-trip to the GPU process, or is it
handled entirely client-side?
2. It looks like when the compositor calls DrawingBuffer::mailboxReleased, the
MailboxInfo contains the previously-queried GPU_MEMORY_BUFFER_ID, so it doesn't
need to be queried again unless the canvas has changed size. Correct? So in the
steady state we are not making this call every frame?

[erikchen, 2016/05/27 01:13:37]

The GMB id is cached client side.
That's correct. The only time we make this call is immediately after
CreateGpuMemoryBufferImageCHROMIUM.

+    DCHECK_NE(-1, gpuMemoryBufferId);
 
     TextureInfo info;
     info.textureId = textureId;
     info.imageId = imageId;
+    info.gpuMemoryBufferId = gpuMemoryBufferId;
     info.parameters = parameters;
     clearChromiumImageAlpha(info);
     return info;
 }
 
 DrawingBuffer::TextureInfo DrawingBuffer::createDefaultTextureAndAllocateMemory(const IntSize& size)
 {
     TextureParameters parameters = defaultTextureParameters();
     GLuint textureId = createColorTexture(parameters);
     texImage2DResourceSafe(parameters.target, 0, parameters.creationInternalColorFormat, size.width(), size.height(), 0, parameters.colorFormat, GL_UNSIGNED_BYTE);
 
     DrawingBuffer::TextureInfo info;
     info.textureId = textureId;
     info.parameters = parameters;
     return info;
 }
 
 void DrawingBuffer::resizeTextureMemory(TextureInfo* info, const IntSize& size)
 {
     ASSERT(info->textureId);
     if (info->imageId) {
         deleteChromiumImageForTexture(info);
         info->imageId = m_gl->CreateGpuMemoryBufferImageCHROMIUM(size.width(), size.height(), info->parameters.creationInternalColorFormat, GC3D_SCANOUT_CHROMIUM);
         if (info->imageId) {
             m_gl->BindTexture(info->parameters.target, info->textureId);
             m_gl->BindTexImage2DCHROMIUM(info->parameters.target, info->imageId);
+
+            GLint gpuMemoryBufferId = -1;
+            m_gl->GetImageivCHROMIUM(info->imageId, GC3D_GPU_MEMORY_BUFFER_ID, &gpuMemoryBufferId);
+            DCHECK_NE(-1, gpuMemoryBufferId);
+            info->gpuMemoryBufferId = gpuMemoryBufferId;
+
             clearChromiumImageAlpha(*info);
             return;
         }
 
         // If the desired texture target is different, there's no way to fall back
         // to a non CHROMIUM_image texture.
         if (chromiumImageTextureParameters().target != defaultTextureParameters().target)
             return;
     }
 
@@ skipping 41 matching lines @@
 
 void DrawingBuffer::restoreTextureBindings()
 {
     // This class potentially modifies the bindings for GL_TEXTURE_2D and
     // GL_TEXTURE_RECTANGLE. Only GL_TEXTURE_2D needs to be restored since
     // the public interface for WebGL does not support GL_TEXTURE_RECTANGLE.
     m_gl->BindTexture(GL_TEXTURE_2D, m_texture2DBinding);
 }
 
 } // namespace blink