WebGL GL_RGB emulation to support IOSurfaces on Mac.

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

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 0810046dd880bf754b1eab8f2f66eb95d608d6c5..4eed48c5a7d9116a2fc1843c5eae2a63d6f88de7 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -242,6 +242,15 @@ void DrawingBuffer::setFilterQuality(SkFilterQuality filterQuality)
     }
 }
 
+bool DrawingBuffer::requiresRGBEmulation()
+{
+#if OS(MACOSX)
+    return !m_drawFramebufferBinding && !m_wantAlphaChannel && m_colorBuffer.imageId;
+#else
+    return false;
+#endif
+}
+
 void DrawingBuffer::freeRecycledMailboxes()
 {
     if (m_recycledMailboxQueue.isEmpty())
@@ -360,9 +369,11 @@ DrawingBuffer::TextureParameters DrawingBuffer::chromiumImageTextureParameters()
     // on OSX.
     TextureParameters parameters;
     parameters.target = GC3D_TEXTURE_RECTANGLE_ARB;
-    parameters.internalColorFormat = GL_BGRA_EXT;
+    parameters.internalColorFormat = GL_RGBA;
     parameters.internalRenderbufferFormat = GL_RGBA8_OES;
-    parameters.colorFormat = GL_RGBA;
+
+    // Unused.
+    parameters.colorFormat = 0;
     return parameters;
 #else
     return defaultTextureParameters();
@@ -764,7 +775,7 @@ bool DrawingBuffer::reset(const IntSize& newSize, bool wantDepthOrStencilBuffer)
 
     m_gl->Disable(GL_SCISSOR_TEST);
     m_gl->ClearColor(0, 0, 0, 0);
-    m_gl->ColorMask(true, true, true, true);
+    m_gl->ColorMask(true, true, true, !requiresRGBEmulation());
 
     GLbitfield clearMask = GL_COLOR_BUFFER_BIT;
     if (!!m_depthStencilBuffer) {
@@ -779,6 +790,7 @@ bool DrawingBuffer::reset(const IntSize& newSize, bool wantDepthOrStencilBuffer)
     }
 
     clearFramebuffers(clearMask);
+    m_gl->ColorMask(true, true, true, true);
     return true;
 }
 
@@ -948,14 +960,25 @@ void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
     }
 }
 
-DrawingBuffer::TextureInfo DrawingBuffer::createTextureAndAllocateMemory(const IntSize& size)
+void DrawingBuffer::clearChromiumImageIfNecessary(const TextureInfo& info)
 {
-    // TODO(erikchen): Add support for a CHROMIUM_image back buffer whose
-    // behavior mimics a texture with internal format GL_RGB.
-    // https://crbug.com/581777.
-    if (!m_wantAlphaChannel)
-        return createDefaultTextureAndAllocateMemory(size);
+    if (m_wantAlphaChannel)
+        return;
 
+    GLuint fbo = 0;
+    m_gl->GenFramebuffers(1, &fbo);
+    m_gl->BindFramebuffer(GL_FRAMEBUFFER, fbo);
+    m_gl->FramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, info.parameters.target, info.textureId, 0);
+    m_gl->ClearColor(0, 0, 0, 1);
+    m_gl->ColorMask(false, false, false, true);
+    m_gl->Clear(GL_COLOR_BUFFER_BIT);
+    m_gl->FramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, info.parameters.target, 0, 0);
+    m_gl->DeleteFramebuffers(1, &fbo);
+    restoreFramebufferBindings();
+}
+
+DrawingBuffer::TextureInfo DrawingBuffer::createTextureAndAllocateMemory(const IntSize& size)
+{
     if (!RuntimeEnabledFeatures::webGLImageChromiumEnabled())
         return createDefaultTextureAndAllocateMemory(size);
 
@@ -973,6 +996,7 @@ DrawingBuffer::TextureInfo DrawingBuffer::createTextureAndAllocateMemory(const I
     info.textureId = textureId;
     info.imageId = imageId;
     info.parameters = parameters;
+    clearChromiumImageIfNecessary(info);
     return info;
 }
 
@@ -997,6 +1021,7 @@ void DrawingBuffer::resizeTextureMemory(TextureInfo* info, const IntSize& size)
         if (info->imageId) {
             m_gl->BindTexture(info->parameters.target, info->textureId);
             m_gl->BindTexImage2DCHROMIUM(info->parameters.target, info->imageId);
+            clearChromiumImageIfNecessary(*info);
             return;
         }