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

Source/WebCore/platform/graphics/gpu/DrawingBuffer.cpp

Index: Source/WebCore/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/Source/WebCore/platform/graphics/gpu/DrawingBuffer.cpp b/Source/WebCore/platform/graphics/gpu/DrawingBuffer.cpp
index 5fb5f07ea524cc2dceaf05944b0a1dbaf397a9f6..2553465285e39dbb5937884f7f2ef348979a688f 100644
--- a/Source/WebCore/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/Source/WebCore/platform/graphics/gpu/DrawingBuffer.cpp
@@ -39,6 +39,7 @@
 #include "GraphicsLayerChromium.h"
 #include "ImageData.h"
 #include "TraceEvent.h"
+#include "WebGLRenderingContext.h"
 #include <algorithm>
 #include <public/Platform.h>
 #include <public/WebCompositorSupport.h>
@@ -55,6 +56,7 @@ namespace WebCore {
 static int s_maximumResourceUsePixels = 16 * 1024 * 1024;
 static int s_currentResourceUsePixels = 0;
 static const float s_resourceAdjustedRatio = 0.5;
+static const int s_maxScaleAttempts = 3;
 
 static unsigned generateColorTexture(GraphicsContext3D* context, const IntSize& size)
 {
@@ -109,11 +111,11 @@ DrawingBuffer::DrawingBuffer(GraphicsContext3D* context,
 
 DrawingBuffer::~DrawingBuffer()
 {
+    clear();
+
     if (!m_context)
         return;
 
-    clear();
-
     if (m_layer)
         GraphicsLayerChromium::unregisterContentsLayer(m_layer->layer());
 }
@@ -262,57 +264,49 @@ PassRefPtr<DrawingBuffer> DrawingBuffer::create(GraphicsContext3D* context, cons
 
 void DrawingBuffer::clear()
 {
-    if (!m_context)
-        return;
+    if (m_context) {
+        m_context->makeContextCurrent();
 
-    m_context->makeContextCurrent();
+        clearPlatformLayer();
 
-    clearPlatformLayer();
+        if (m_colorBuffer)
+            m_context->deleteTexture(m_colorBuffer);
 
-    if (!m_size.isEmpty()) {
-        s_currentResourceUsePixels -= m_size.width() * m_size.height();
-        m_size = IntSize();
-    }
+        if (m_frontColorBuffer)
+            m_context->deleteTexture(m_frontColorBuffer);
 
-    if (m_colorBuffer) {
-        m_context->deleteTexture(m_colorBuffer);
-        m_colorBuffer = 0;
-    }
+        if (m_multisampleColorBuffer)
+            m_context->deleteRenderbuffer(m_multisampleColorBuffer);
 
-    if (m_frontColorBuffer) {
-        m_context->deleteTexture(m_frontColorBuffer);
-        m_frontColorBuffer = 0;
-    }
+        if (m_depthStencilBuffer)
+            m_context->deleteRenderbuffer(m_depthStencilBuffer);
 
-    if (m_multisampleColorBuffer) {
-        m_context->deleteRenderbuffer(m_multisampleColorBuffer);
-        m_multisampleColorBuffer = 0;
-    }
+        if (m_depthBuffer)
+            m_context->deleteRenderbuffer(m_depthBuffer);
 
-    if (m_depthStencilBuffer) {
-        m_context->deleteRenderbuffer(m_depthStencilBuffer);
-        m_depthStencilBuffer = 0;
-    }
+        if (m_stencilBuffer)
+            m_context->deleteRenderbuffer(m_stencilBuffer);
 
-    if (m_depthBuffer) {
-        m_context->deleteRenderbuffer(m_depthBuffer);
-        m_depthBuffer = 0;
-    }
+        if (m_multisampleFBO)
+            m_context->deleteFramebuffer(m_multisampleFBO);
 
-    if (m_stencilBuffer) {
-        m_context->deleteRenderbuffer(m_stencilBuffer);
-        m_stencilBuffer = 0;
+        if (m_fbo)
+            m_context->deleteFramebuffer(m_fbo);
     }
 
-    if (m_multisampleFBO) {
-        m_context->deleteFramebuffer(m_multisampleFBO);
-        m_multisampleFBO = 0;
+    if (!m_size.isEmpty()) {
+        s_currentResourceUsePixels -= m_size.width() * m_size.height();
+        m_size = IntSize();
     }
 
-    if (m_fbo) {
-        m_context->deleteFramebuffer(m_fbo);
-        m_fbo = 0;
-    }
+    m_colorBuffer = 0;
+    m_frontColorBuffer = 0;
+    m_multisampleColorBuffer = 0;
+    m_depthStencilBuffer = 0;
+    m_depthBuffer = 0;
+    m_stencilBuffer = 0;
+    m_multisampleFBO = 0;
+    m_fbo = 0;
 }
 
 void DrawingBuffer::createSecondaryBuffers()
@@ -420,15 +414,31 @@ bool DrawingBuffer::reset(const IntSize& newSize)
 
     int pixelDelta = newSize.width() * newSize.height();
     int oldSize = 0;
+    bool newBuffer = true;
     if (!m_size.isEmpty()) {
         oldSize = m_size.width() * m_size.height();
         pixelDelta -= oldSize;
+        newBuffer = false;
+    }
+
+    if(newBuffer && s_currentResourceUsePixels == s_maximumResourceUsePixels) {
+        WebGLRenderingContext::forceLostOldestContext();
+        newBuffer = false;
     }
 
     IntSize adjustedSize = newSize;
+    int scaleAttempts = 0;
     if (s_maximumResourceUsePixels) {
         while ((s_currentResourceUsePixels + pixelDelta) > s_maximumResourceUsePixels) {
             adjustedSize.scale(s_resourceAdjustedRatio);
+
+            scaleAttempts++;
+            if(newBuffer && scaleAttempts >= s_maxScaleAttempts) {
+                WebGLRenderingContext::forceLostOldestContext();
+                adjustedSize = newSize;
+                newBuffer = false;
+            }
+
             if (adjustedSize.isEmpty()) {
                 clear();
                 return false;