Free temporary GPU and memory resources held by inactive or hidden 2D canvases

Source/core/html/HTMLCanvasElement.h

 /*
  * Copyright (C) 2004, 2006, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 13 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef HTMLCanvasElement_h
 #define HTMLCanvasElement_h
 
 #include "core/html/HTMLElement.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/IntSize.h"
+#include "platform/graphics/Canvas2DLayerBridge.h"
 #include "wtf/Forward.h"
 
 #define DefaultInterpolationQuality InterpolationMedium
 
 namespace WebCore {
 
 class CanvasContextAttributes;
 class CanvasRenderingContext;
 class GraphicsContext;
 class GraphicsContextStateSaver;
 class HTMLCanvasElement;
 class Image;
 class ImageData;
 class ImageBuffer;
 class ImageBufferSurface;
 class IntSize;
 
 class CanvasObserver {
 public:
     virtual ~CanvasObserver() { }
 
     virtual void canvasChanged(HTMLCanvasElement*, const FloatRect& changedRect) = 0;
     virtual void canvasResized(HTMLCanvasElement*) = 0;
     virtual void canvasDestroyed(HTMLCanvasElement*) = 0;
 };
 
-class HTMLCanvasElement FINAL : public HTMLElement {
+class HTMLCanvasElement FINAL : public HTMLElement, public Canvas2DLayerBridgeClient {
 public:
     static PassRefPtr<HTMLCanvasElement> create(Document&);
     virtual ~HTMLCanvasElement();
 
     void addObserver(CanvasObserver*);
     void removeObserver(CanvasObserver*);
 
     // Attributes and functions exposed to script
     int width() const { return size().width(); }
     int height() const { return size().height(); }
@@ skipping 47 matching lines @@
     AffineTransform baseTransform() const;
 
     bool is3D() const;
 
     bool hasImageBuffer() const { return m_imageBuffer.get(); }
 
     bool shouldAccelerate(const IntSize&) const;
 
     InsertionNotificationRequest insertedInto(ContainerNode*) OVERRIDE;
 
+    // Canvas2DLayerBridgeClient implementation
+    virtual bool hidden() const OVERRIDE { return document().hidden(); }

[eseidel, 2013/12/19 02:56:32]

Why do these individual elements know if they're hidden or not?

Shouldn't we just be signing up for some sort of "left the viewport" or "page
visibility chagned" notifications by things which care and then telling them via
some event/callback?

+
 private:
     explicit HTMLCanvasElement(Document&);
 
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) OVERRIDE;
     virtual RenderObject* createRenderer(RenderStyle*);
     virtual bool areAuthorShadowsAllowed() const OVERRIDE { return false; }
 
     void reset();
 
     PassOwnPtr<ImageBufferSurface> createImageBufferSurface(const IntSize& deviceSize, int* msaaSampleCount);
@@ skipping 31 matching lines @@
 
     mutable RefPtr<Image> m_presentedImage;
     mutable RefPtr<Image> m_copiedImage; // FIXME: This is temporary for platforms that have to copy the image buffer to render (and for CSSCanvasValue).
 };
 
 DEFINE_NODE_TYPE_CASTS(HTMLCanvasElement, hasTagName(HTMLNames::canvasTag));
 
 } //namespace
 
 #endif