Enable anti-alias in WebGL if only GL_EXT_multisampled_render_to_texture is supported.

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 76 matching lines @@
 } // namespace
 
 PassRefPtr<DrawingBuffer> DrawingBuffer::create(PassOwnPtr<WebGraphicsContext3D> context, const IntSize& size, PreserveDrawingBuffer preserve, WebGraphicsContext3D::Attributes requestedAttributes, PassRefPtr<ContextEvictionManager> contextEvictionManager)
 {
     ASSERT(context);
     OwnPtr<Extensions3DUtil> extensionsUtil = Extensions3DUtil::create(context.get());
     if (!extensionsUtil) {
         // This might be the first time we notice that the WebGraphicsContext3D is lost.
         return nullptr;
     }
-    bool multisampleSupported = extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample")
+    bool multisampleSupported = (extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample")
+        || extensionsUtil->supportsExtension("GL_EXT_multisampled_render_to_texture"))

[Ken Russell (switch to Gerrit), 2014/10/31 23:23:42]

The code in DrawingBuffer::initialize already checks for the
GL_EXT_multisampled_render_to_texture extension, and I'm quite sure that code
path has been tested. Is your patch for the case where the hardware can't
support GL_CHROMIUM_framebuffer_multisample, but does support
GL_EXT_multisampled_render_to_texture? Do you have an example of such hardware
on which we could verify this fix?

Could you please file a bug about this and reference crbug.com/322706 ?

         && extensionsUtil->supportsExtension("GL_OES_rgb8_rgba8");
     if (multisampleSupported) {

[Ken Russell (switch to Gerrit), 2014/11/03 22:47:52]

Please factor out the call to ensureExtensionEnabled("GL_OES_rgb8_rgba8") so
it's only called once on this code path.

-        extensionsUtil->ensureExtensionEnabled("GL_CHROMIUM_framebuffer_multisample");
-        extensionsUtil->ensureExtensionEnabled("GL_OES_rgb8_rgba8");
+        if (extensionsUtil->supportsExtension("GL_CHROMIUM_framebuffer_multisample") {
+            extensionsUtil->ensureExtensionEnabled("GL_CHROMIUM_framebuffer_multisample");
+            extensionsUtil->ensureExtensionEnabled("GL_OES_rgb8_rgba8");
+        } else {
+            extensionsUtil->ensureExtensionEnabled("GL_EXT_multisampled_render_to_texture");
+            extensionsUtil->ensureExtensionEnabled("GL_OES_rgb8_rgba8");
+        }
     }
     bool packedDepthStencilSupported = extensionsUtil->supportsExtension("GL_OES_packed_depth_stencil");
     if (packedDepthStencilSupported)
         extensionsUtil->ensureExtensionEnabled("GL_OES_packed_depth_stencil");
     bool discardFramebufferSupported = extensionsUtil->supportsExtension("GL_EXT_discard_framebuffer");
     if (discardFramebufferSupported)
         extensionsUtil->ensureExtensionEnabled("GL_EXT_discard_framebuffer");
 
     RefPtr<DrawingBuffer> drawingBuffer = adoptRef(new DrawingBuffer(context, extensionsUtil.release(), multisampleSupported, packedDepthStencilSupported, discardFramebufferSupported, preserve, requestedAttributes, contextEvictionManager));
     if (!drawingBuffer->initialize(size)) {
@@ skipping 948 matching lines @@
 void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
 {
     if (info->imageId) {
         m_context->releaseTexImage2DCHROMIUM(GL_TEXTURE_2D, info->imageId);
         m_context->destroyImageCHROMIUM(info->imageId);
         info->imageId = 0;
     }
 }
 
 } // namespace blink