Lose/restore WebGL contexts if multisampling blackist status changes at runtime.

Source/core/html/canvas/WebGLRenderingContext.cpp

Index: Source/core/html/canvas/WebGLRenderingContext.cpp
diff --git a/Source/core/html/canvas/WebGLRenderingContext.cpp b/Source/core/html/canvas/WebGLRenderingContext.cpp
index 34cf1793dff9881e7320d7f5595e53d10af9f036..ed1f58ab12235f70711ea5cc9e176dd95d0c40ce 100644
--- a/Source/core/html/canvas/WebGLRenderingContext.cpp
+++ b/Source/core/html/canvas/WebGLRenderingContext.cpp
@@ -450,6 +450,15 @@ namespace {
             break;
         }
     }
+
+    GraphicsContext3D::Attributes adjustAttributes(GraphicsContext3D::Attributes attributes, Settings* settings) {

[Ken Russell (switch to Gerrit), 2013/05/08 02:17:02]

Passing the GraphicsContext3D::Attributes by value, mutating it and then
returning a copy is a little gross and confusing to read. Prefer to pass a const
reference, allocate a new GraphicsContext3D::Attributes on the stack in this
function copying the input, and adjust the outgoing copy.

+        if (attributes.antialias) {
+            if (settings && !settings->openGLMultisamplingEnabled())
+                attributes.antialias = false;
+        }
+
+        return attributes;
+    }
 } // namespace anonymous
 
 class WebGLRenderingContextLostCallback : public GraphicsContext3D::ContextLostCallback {
@@ -492,17 +501,13 @@ PassOwnPtr<WebGLRenderingContext> WebGLRenderingContext::create(HTMLCanvasElemen
     }
 
     HostWindow* hostWindow = document->view()->root()->hostWindow();
-    GraphicsContext3D::Attributes attributes = attrs ? attrs->attributes() : GraphicsContext3D::Attributes();
+    GraphicsContext3D::Attributes requestedAttributes = attrs ? attrs->attributes() : GraphicsContext3D::Attributes();
+    requestedAttributes.noExtensions = true;
+    requestedAttributes.shareResources = true;
+    requestedAttributes.preferDiscreteGPU = true;
+    requestedAttributes.topDocumentURL = document->topDocument()->url();
 
-    if (attributes.antialias) {
-        if (settings && !settings->openGLMultisamplingEnabled())
-            attributes.antialias = false;
-    }
-
-    attributes.noExtensions = true;
-    attributes.shareResources = true;
-    attributes.preferDiscreteGPU = true;
-    attributes.topDocumentURL = document->topDocument()->url();
+    GraphicsContext3D::Attributes attributes = adjustAttributes(requestedAttributes, settings);
 
     RefPtr<GraphicsContext3D> context(GraphicsContext3D::create(attributes, hostWindow));
 
@@ -515,7 +520,7 @@ PassOwnPtr<WebGLRenderingContext> WebGLRenderingContext::create(HTMLCanvasElemen
     if (extensions->supports("GL_EXT_debug_marker"))
         extensions->pushGroupMarkerEXT("WebGLRenderingContext");
 
-    OwnPtr<WebGLRenderingContext> renderingContext = adoptPtr(new WebGLRenderingContext(canvas, context, attributes));
+    OwnPtr<WebGLRenderingContext> renderingContext = adoptPtr(new WebGLRenderingContext(canvas, context, attributes, requestedAttributes));
     renderingContext->suspendIfNeeded();
 
     if (renderingContext->m_drawingBuffer->isZeroSized()) {
@@ -527,7 +532,8 @@ PassOwnPtr<WebGLRenderingContext> WebGLRenderingContext::create(HTMLCanvasElemen
 }
 
 WebGLRenderingContext::WebGLRenderingContext(HTMLCanvasElement* passedCanvas, PassRefPtr<GraphicsContext3D> context,
-                                             GraphicsContext3D::Attributes attributes)
+                                             GraphicsContext3D::Attributes attributes,
+                                             GraphicsContext3D::Attributes requestedAttributes)
     : CanvasRenderingContext(passedCanvas)
     , ActiveDOMObject(passedCanvas->document())
     , m_context(context)
@@ -539,6 +545,7 @@ WebGLRenderingContext::WebGLRenderingContext(HTMLCanvasElement* passedCanvas, Pa
     , m_contextLost(false)
     , m_contextLostMode(SyntheticLostContext)
     , m_attributes(attributes)
+    , m_requestedAttributes(requestedAttributes)
     , m_synthesizedErrorsToConsole(true)
     , m_numGLErrorsToConsoleAllowed(maxGLErrorsAllowedToConsole)
 {
@@ -646,9 +653,13 @@ void WebGLRenderingContext::setupFlags()
     ASSERT(m_context);
 
     Page* p = canvas()->document()->page();
-    if (p)
+    if (p) {
         m_synthesizedErrorsToConsole = p->settings()->webGLErrorsToConsoleEnabled();
 
+        if (m_multisamplingChangedObserver == 0 && m_requestedAttributes.antialias)

[Ken Russell (switch to Gerrit), 2013/05/08 02:17:02]

Nit: style guide would say "if (!m_multisamplingChangedObserver && ...".

+            m_multisamplingChangedObserver = adoptRef(new WebGLMultisamplingChangedObserver(this, p));
+    }
+
     m_isGLES2NPOTStrict = !m_context->getExtensions()->isEnabled("GL_OES_texture_npot");
     m_isDepthStencilSupported = m_context->getExtensions()->isEnabled("GL_OES_packed_depth_stencil");
     m_isRobustnessEXTSupported = m_context->getExtensions()->isEnabled("GL_EXT_robustness");
@@ -5244,7 +5255,7 @@ void WebGLRenderingContext::dispatchContextLostEvent(Timer<WebGLRenderingContext
     canvas()->dispatchEvent(event);
     m_restoreAllowed = event->defaultPrevented();
     deactivateContext(this, m_contextLostMode != RealLostContext && m_restoreAllowed);
-    if (m_contextLostMode == RealLostContext && m_restoreAllowed)
+    if ((m_contextLostMode == RealLostContext || m_contextLostMode == AutoRecoverSyntheticLostContext) && m_restoreAllowed)
         m_restoreTimer.startOneShot(0);
 }
 
@@ -5268,7 +5279,9 @@ void WebGLRenderingContext::maybeRestoreContext(Timer<WebGLRenderingContext>*)
     if (!frame)
         return;
 
-    if (!frame->loader()->client()->allowWebGL(frame->settings() && frame->settings()->webGLEnabled()))
+    Settings* settings = frame->settings();
+
+    if (!frame->loader()->client()->allowWebGL(settings && settings->webGLEnabled()))
         return;
 
     FrameView* view = frame->view();
@@ -5281,6 +5294,9 @@ void WebGLRenderingContext::maybeRestoreContext(Timer<WebGLRenderingContext>*)
     if (!hostWindow)
         return;
 
+    // Reset the context attributes back to the requested attributes and re-apply restrictions
+    m_attributes = adjustAttributes(m_requestedAttributes, settings);
+
     RefPtr<GraphicsContext3D> context(GraphicsContext3D::create(m_attributes, hostWindow));
     if (!context) {
         if (m_contextLostMode == RealLostContext)
@@ -5471,4 +5487,19 @@ void WebGLRenderingContext::restoreCurrentTexture2D()
     bindTexture(GraphicsContext3D::TEXTURE_2D, m_textureUnits[m_activeTextureUnit].m_texture2DBinding.get(), ec);
 }
 
+WebGLRenderingContext::WebGLMultisamplingChangedObserver::WebGLMultisamplingChangedObserver(WebGLRenderingContext* context, Page* page)
+    : m_context(context)
+    , Page::MultisamplingChangedObserver(page)
+{
+    m_multisamplingAllowed = m_context->getContextAttributes()->antialias();
+}
+
+void WebGLRenderingContext::WebGLMultisamplingChangedObserver::multisamplingChanged(bool enabled)
+{
+    if (m_multisamplingAllowed != enabled) {
+        m_multisamplingAllowed = enabled;
+        m_context->forceLostContext(WebGLRenderingContext::AutoRecoverSyntheticLostContext);
+    }
+}
+
 } // namespace WebCore