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

Source/core/html/canvas/WebGLRenderingContext.cpp

 /*
  * Copyright (C) 2009 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 432 matching lines @@
                 advance();
                 break;
             }
 
             // Swallow all other characters. Unclear whether we may
             // want or need to just emit a space per character to try
             // to preserve column numbers for debugging purposes.
             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 {
     WTF_MAKE_FAST_ALLOCATED;
 public:
     explicit WebGLRenderingContextLostCallback(WebGLRenderingContext* cb) : m_context(cb) { }
     virtual void onContextLost() { m_context->forceLostContext(WebGLRenderingContext::RealLostContext); }
     virtual ~WebGLRenderingContextLostCallback() {}
 private:
     WebGLRenderingContext* m_context;
@@ skipping 22 matching lines @@
     Settings* settings = frame->settings();
 
     // The FrameLoaderClient might block creation of a new WebGL context despite the page settings; in
     // particular, if WebGL contexts were lost one or more times via the GL_ARB_robustness extension.
     if (!frame->loader()->client()->allowWebGL(settings && settings->webGLEnabled())) {
         canvas->dispatchEvent(WebGLContextEvent::create(eventNames().webglcontextcreationerrorEvent, false, true, "Web page was not allowed to create a WebGL context."));
         return nullptr;
     }
 
     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));
 
     if (!context || !context->makeContextCurrent()) {
         canvas->dispatchEvent(WebGLContextEvent::create(eventNames().webglcontextcreationerrorEvent, false, true, "Could not create a WebGL context."));
         return nullptr;
     }
 
     Extensions3D* extensions = context->getExtensions();
     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()) {
         canvas->dispatchEvent(WebGLContextEvent::create(eventNames().webglcontextcreationerrorEvent, false, true, "Could not create a WebGL context."));
         return nullptr;
     }
 
     return renderingContext.release();
 }
 
 WebGLRenderingContext::WebGLRenderingContext(HTMLCanvasElement* passedCanvas, PassRefPtr<GraphicsContext3D> context,
-                                             GraphicsContext3D::Attributes attributes)
+                                             GraphicsContext3D::Attributes attributes,
+                                             GraphicsContext3D::Attributes requestedAttributes)
     : CanvasRenderingContext(passedCanvas)
     , ActiveDOMObject(passedCanvas->document())
     , m_context(context)
     , m_drawingBuffer(0)
     , m_dispatchContextLostEventTimer(this, &WebGLRenderingContext::dispatchContextLostEvent)
     , m_restoreAllowed(false)
     , m_restoreTimer(this, &WebGLRenderingContext::maybeRestoreContext)
     , m_videoCache(4)
     , m_contextLost(false)
     , m_contextLostMode(SyntheticLostContext)
     , m_attributes(attributes)
+    , m_requestedAttributes(requestedAttributes)
     , m_synthesizedErrorsToConsole(true)
     , m_numGLErrorsToConsoleAllowed(maxGLErrorsAllowedToConsole)
 {
     ASSERT(m_context);
     ScriptWrappable::init(this);
 
     m_contextGroup = WebGLContextGroup::create();
     m_contextGroup->addContext(this);
 
     m_maxViewportDims[0] = m_maxViewportDims[1] = 0;
@@ skipping 87 matching lines @@
     m_context->setErrorMessageCallback(adoptPtr(new WebGLRenderingContextErrorMessageCallback(this)));
 
     activateContext(this);
 }
 
 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");
 }
 
 bool WebGLRenderingContext::allowPrivilegedExtensions() const
 {
     Page* p = canvas()->document()->page();
     if (p && p->settings())
         return p->settings()->privilegedWebGLExtensionsEnabled();
@@ skipping 4575 matching lines @@
     for (int ii = 0; ii < expectedSize; ++ii)
         attribValue.value[ii] = v[ii];
 }
 
 void WebGLRenderingContext::dispatchContextLostEvent(Timer<WebGLRenderingContext>*)
 {
     RefPtr<WebGLContextEvent> event = WebGLContextEvent::create(eventNames().webglcontextlostEvent, false, true, "");
     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);
 }
 
 void WebGLRenderingContext::maybeRestoreContext(Timer<WebGLRenderingContext>*)
 {
     ASSERT(isContextLost());
 
     // The rendering context is not restored unless the default behavior of the
     // webglcontextlost event was prevented earlier.
     //
     // Because of the way m_restoreTimer is set up for real vs. synthetic lost
     // context events, we don't have to worry about this test short-circuiting
     // the retry loop for real context lost events.
     if (!m_restoreAllowed)
         return;
 
     Document* document = canvas()->document();
     if (!document)
         return;
     Frame* frame = document->frame();
     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();
     if (!view)
         return;
     ScrollView* root = view->root();
     if (!root)
         return;
     HostWindow* hostWindow = root->hostWindow();
     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)
             m_restoreTimer.startOneShot(secondsBetweenRestoreAttempts);
         else
             // This likely shouldn't happen but is the best way to report it to the WebGL app.
             synthesizeGLError(GraphicsContext3D::INVALID_OPERATION, "", "error restoring context");
         return;
     }
 
@@ skipping 170 matching lines @@
     ExceptionCode ec;
     bindFramebuffer(GraphicsContext3D::FRAMEBUFFER, m_framebufferBinding.get(), ec);
 }
 
 void WebGLRenderingContext::restoreCurrentTexture2D()
 {
     ExceptionCode ec;
     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