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

Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 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 53 matching lines @@
 // Firefox limits width/height to 32767 pixels, but slows down dramatically before it
 // reaches that limit. We limit by area instead, giving us larger maximum dimensions,
 // in exchange for a smaller maximum canvas size.
 static const int MaxCanvasArea = 32768 * 8192; // Maximum canvas area in CSS pixels
 
 //In Skia, we will also limit width/height to 32767.
 static const int MaxSkiaDim = 32767; // Maximum width/height in CSS pixels.
 
 HTMLCanvasElement::HTMLCanvasElement(Document& document)
     : HTMLElement(canvasTag, document)
+    , DocumentVisibilityObserver(document)
     , m_size(DefaultWidth, DefaultHeight)
     , m_rendererIsCanvas(false)
     , m_ignoreReset(false)
     , m_accelerationDisabled(false)
     , m_externallyAllocatedMemory(0)
     , m_originClean(true)
     , m_didFailToCreateImageBuffer(false)
     , m_didClearImageBuffer(false)
 {
     ScriptWrappable::init(this);
@@ skipping 480 matching lines @@
     m_copiedImage.clear();
     m_didClearImageBuffer = false;
 }
 
 AffineTransform HTMLCanvasElement::baseTransform() const
 {
     ASSERT(hasImageBuffer() && !m_didFailToCreateImageBuffer);
     return m_imageBuffer->baseTransform();
 }
 
+void HTMLCanvasElement::didChangeVisibilityState(PageVisibilityState visibility)
+{
+    if (hasImageBuffer()) {
+        bool hidden = visibility != PageVisibilityStateVisible;
+        if (hidden) {
+            clearCopiedImage();
+            if (is3D()) {
+                m_imageBuffer.clear();
+            }
+        }
+        if (hasImageBuffer()) {
+            m_imageBuffer->setIsHidden(hidden);
+        }
+    }
 }
+
+void HTMLCanvasElement::didMoveToNewDocument(Document& oldDocument)
+{
+    setObservedDocument(document());
+    HTMLElement::didMoveToNewDocument(oldDocument);
+}
+
+}