Share Group plumbing in Blink; Remove WebGL from default share group

Source/platform/graphics/ImageBuffer.cpp

Index: Source/platform/graphics/ImageBuffer.cpp
diff --git a/Source/platform/graphics/ImageBuffer.cpp b/Source/platform/graphics/ImageBuffer.cpp
index 6a207636bf19815b99422040a47429b3e8136c54..4485c50d31857cb5293829532afc8dab0f52d55b 100644
--- a/Source/platform/graphics/ImageBuffer.cpp
+++ b/Source/platform/graphics/ImageBuffer.cpp
@@ -47,6 +47,7 @@
 #include "platform/image-encoders/skia/PNGImageEncoder.h"
 #include "platform/image-encoders/skia/WEBPImageEncoder.h"
 #include "public/platform/Platform.h"
+#include "public/platform/WebExternalTextureMailbox.h"
 #include "public/platform/WebGraphicsContext3D.h"
 #include "public/platform/WebGraphicsContext3DProvider.h"
 #include "third_party/skia/include/effects/SkTableColorFilter.h"
@@ -138,22 +139,57 @@ bool ImageBuffer::copyToPlatformTexture(blink::WebGraphicsContext3D* context, Pl
     if (!m_surface->isAccelerated() || !platformLayer() || !isValid())
         return false;
 
-    if (!context->makeContextCurrent())
+    if (!Extensions3DUtil::canUseCopyTextureCHROMIUM(internalFormat, destType, level))
         return false;
 
-    if (!Extensions3DUtil::canUseCopyTextureCHROMIUM(internalFormat, destType, level))
+    OwnPtr<blink::WebGraphicsContext3DProvider> provider = adoptPtr(blink::Platform::current()->createSharedOffscreenGraphicsContext3DProvider());
+    if (!provider)
         return false;
+    blink::WebGraphicsContext3D* sharedContext = provider->context3d();
+    if (!sharedContext || !sharedContext->makeContextCurrent())
+        return false;
+
+    GLint boundTexture = 0;
+    sharedContext->getIntegerv(GL_TEXTURE_BINDING_2D, &boundTexture);

[Ken Russell (switch to Gerrit), 2014/03/12 21:23:38]

Get calls are expensive in the command buffer. Is it really necessary to
preserve the texture bound to the current active texture unit in the shared
context? If it's used in a stateless fashion by the calling code (probably Blink
and Ganesh?) then this save/restore can be skipped. In that case,
ImageBuffer::copyToPlatformTexture should document that it destroys the
TEXTURE_2D binding of the active texture unit of the context provided by Blink's
SharedOffscreenGraphicsContext3DProvider.

+
+    OwnPtr<blink::WebExternalTextureMailbox> mailbox = adoptPtr(new blink::WebExternalTextureMailbox);
+
+    // Contexts may be in a different share group. We must transfer the texture through a mailbox first
+    sharedContext->genMailboxCHROMIUM(mailbox->name);
+    sharedContext->bindTexture(GL_TEXTURE_2D, getBackingTexture());
+    sharedContext->produceTextureCHROMIUM(GL_TEXTURE_2D, mailbox->name);
+    sharedContext->bindTexture(GL_TEXTURE_2D, boundTexture);
+    sharedContext->flush();
+
+    mailbox->syncPoint = sharedContext->insertSyncPoint();
+
+    if (!context->makeContextCurrent())
+        return false;
+
+    Platform3DObject sourceTexture = context->createTexture();
+
+    context->getIntegerv(GL_TEXTURE_BINDING_2D, &boundTexture);

[Ken Russell (switch to Gerrit), 2014/03/12 21:23:38]

The only caller of ImageBuffer::copyToPlatformTexture is
WebGLRenderingContextBase, and it should have enough information to restore the
TEXTURE_2D binding for the current texture unit. I think the documentation for
ImageBuffer::copyToPlatformTexture should clearly state that it destroys the
TEXTURE_2D binding for the active texture unit of the passed context, and then
the calling code should restore it. That will avoid the get query here.

+    context->bindTexture(GL_TEXTURE_2D, sourceTexture);
+
+    context->waitSyncPoint(mailbox->syncPoint);
+    context->consumeTextureCHROMIUM(GL_TEXTURE_2D, mailbox->name);
 
     // The canvas is stored in a premultiplied format, so unpremultiply if necessary.
     context->pixelStorei(GC3D_UNPACK_UNPREMULTIPLY_ALPHA_CHROMIUM, !premultiplyAlpha);
 
     // The canvas is stored in an inverted position, so the flip semantics are reversed.
     context->pixelStorei(GC3D_UNPACK_FLIP_Y_CHROMIUM, !flipY);
-    context->copyTextureCHROMIUM(GL_TEXTURE_2D, getBackingTexture(), texture, level, internalFormat, destType);
+    context->copyTextureCHROMIUM(GL_TEXTURE_2D, sourceTexture, texture, level, internalFormat, destType);
 
     context->pixelStorei(GC3D_UNPACK_FLIP_Y_CHROMIUM, false);
     context->pixelStorei(GC3D_UNPACK_UNPREMULTIPLY_ALPHA_CHROMIUM, false);
+
+    context->bindTexture(GL_TEXTURE_2D, boundTexture);

[Ken Russell (switch to Gerrit), 2014/03/12 21:23:38]

In order to effectively delete sourceTexture below, this could bind NULL.

+    context->deleteTexture(sourceTexture);
+
     context->flush();
+    sharedContext->waitSyncPoint(context->insertSyncPoint());
+
     return true;
 }