Limit the number of WebGL contexts that are active at any given time

Source/core/platform/graphics/gpu/DrawingBuffer.h

 /*
  * 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 33 matching lines @@
 
 namespace WebKit {
 class WebExternalTextureLayer;
 class WebGraphicsContext3D;
 }
 
 namespace WebCore {
 class GraphicsContext3D;
 class ImageData;
 
+// Abstract interface to allow basic context eviction management
+class ContextEvictionManager : public RefCounted<ContextEvictionManager> {
+public:
+    virtual ~ContextEvictionManager() {};
+
+    virtual void forciblyLoseOldestContext() = 0;
+    virtual IntSize oldestContextSize() = 0;
+};
+
 // Manages a rendering target (framebuffer + attachment) for a canvas.  Can publish its rendering
 // results to a PlatformLayer for compositing.
 class DrawingBuffer : public RefCounted<DrawingBuffer>, public WebKit::WebExternalTextureLayerClient  {
     struct MailboxInfo : public RefCounted<MailboxInfo> {
         WebKit::WebExternalTextureMailbox mailbox;
         unsigned textureId;
         IntSize size;
     };
 public:
     enum PreserveDrawingBuffer {
         Preserve,
         Discard
     };
 
-    static PassRefPtr<DrawingBuffer> create(GraphicsContext3D*, const IntSize&, PreserveDrawingBuffer);
+    static PassRefPtr<DrawingBuffer> create(GraphicsContext3D*, const IntSize&, PreserveDrawingBuffer, ContextEvictionManager*);
 
     ~DrawingBuffer();
 
     // Clear all resources from this object, as well as context. Called when context is destroyed
     // to prevent invalid accesses to the resources.
     void clear();
 
     // Issues a glClear() on all framebuffers associated with this DrawingBuffer. The caller is responsible for
     // making the context current and setting the clear values and masks. Modifies the framebuffer binding.
     void clearFramebuffers(GC3Dbitfield clearMask);
@@ skipping 35 matching lines @@
     void paintCompositedResultsToCanvas(ImageBuffer*);
 
     // WebExternalTextureLayerClient implementation.
     virtual unsigned prepareTexture(WebKit::WebTextureUpdater& updater) OVERRIDE;
     virtual WebKit::WebGraphicsContext3D* context() OVERRIDE;
     virtual bool prepareMailbox(WebKit::WebExternalTextureMailbox*) OVERRIDE;
     virtual void mailboxReleased(const WebKit::WebExternalTextureMailbox&) OVERRIDE;
 
 private:
     DrawingBuffer(GraphicsContext3D*, const IntSize&, bool multisampleExtensionSupported,
-                  bool packedDepthStencilExtensionSupported, PreserveDrawingBuffer);
+                  bool packedDepthStencilExtensionSupported, PreserveDrawingBuffer, ContextEvictionManager*);

[Ken Russell (switch to Gerrit), 2013/04/24 01:30:57]

This should be PassRefPtr<ContextEvictionManager>.

 
     void initialize(const IntSize&);
 
     void prepareBackBuffer();
     bool requiresCopyFromBackToFrontBuffer() const;
     Platform3DObject frontColorBuffer() const;
     Platform3DObject colorBuffer() const { return m_colorBuffer; }
 
     unsigned createColorTexture(const IntSize& size = IntSize());
     // Create the depth/stencil and multisample buffers, if needed.
@@ skipping 10 matching lines @@
 
     PassRefPtr<MailboxInfo> getRecycledMailbox();
     PassRefPtr<MailboxInfo> createNewMailbox(unsigned);
 
     // Updates the current size of the buffer, ensuring that s_currentResourceUsePixels is updated.
     void setSize(const IntSize& size);
 
     // Calculates the difference in pixels between the current buffer size and the proposed size.
     int pixelDelta(const IntSize& size);
 
+    // Given the desired buffer size, provides the largest dimensions that will fit in the pixel budget
+    // Returns true if the buffer will only fit if the oldest WebGL context is forcibly lost
+    IntSize adjustSizeWithContextEviction(const IntSize&, bool& evictContext);
+
     PreserveDrawingBuffer m_preserveDrawingBuffer;
     bool m_scissorEnabled;
     Platform3DObject m_texture2DBinding;
     Platform3DObject m_framebufferBinding;
     GC3Denum m_activeTextureUnit;
 
     RefPtr<GraphicsContext3D> m_context;
     IntSize m_size;
     bool m_multisampleExtensionSupported;
     bool m_packedDepthStencilExtensionSupported;
@@ skipping 20 matching lines @@
     unsigned m_colorFormat;
     unsigned m_internalRenderbufferFormat;
 
     OwnPtr<WebKit::WebExternalTextureLayer> m_layer;
 
     // All of the mailboxes that this DrawingBuffer has ever created.
     Vector<RefPtr<MailboxInfo> > m_textureMailboxes;
     // Mailboxes that were released by the compositor and can be used again by this DrawingBuffer.
     Vector<RefPtr<MailboxInfo> > m_recycledMailboxes;
     RefPtr<MailboxInfo> m_lastColorBuffer;
+
+    RefPtr<ContextEvictionManager> m_contextEvictionManager;
 };
 
 } // namespace WebCore
 
 #endif // DrawingBuffer_h