Fixing Canvas2DLayerBridge to handle lost graphics contexts

Source/core/platform/graphics/chromium/Canvas2DLayerBridge.cpp

Index: Source/core/platform/graphics/chromium/Canvas2DLayerBridge.cpp
diff --git a/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.cpp b/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.cpp
index 8715c44be61a490d0efe6489bddff8c640e9290d..fd75d8cdbb0189a224a1ea021c7fe1df021321f4 100644
--- a/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.cpp
+++ b/Source/core/platform/graphics/chromium/Canvas2DLayerBridge.cpp
@@ -34,6 +34,7 @@
 #include "core/platform/graphics/GraphicsContext3D.h"
 #include "core/platform/graphics/chromium/Canvas2DLayerManager.h"
 #include "core/platform/graphics/chromium/GraphicsLayerChromium.h"
+#include "core/platform/graphics/gpu/SharedGraphicsContext3D.h"
 #include <public/Platform.h>
 #include <public/WebCompositorSupport.h>
 #include <public/WebGraphicsContext3D.h>
@@ -97,6 +98,13 @@ void Canvas2DLayerBridge::limitPendingFrames()
 
 void Canvas2DLayerBridge::prepareForDraw()
 {
+    if (!contextIsValid()) {
+        if (m_canvas) {
+            // drop pending commands because there is no surface to draw to
+            m_canvas->silentFlush();
+        }
+        return;
+    }
 #if !ENABLE(CANVAS_USES_MAILBOX)
     m_layer->willModifyTexture();
 #endif
@@ -143,6 +151,8 @@ void Canvas2DLayerBridge::flush()
 
 unsigned Canvas2DLayerBridge::prepareTexture(WebTextureUpdater& updater)
 {
+    if (!contextIsValid())
+        return 0;
 #if ENABLE(CANVAS_USES_MAILBOX)
     ASSERT_NOT_REACHED();
     return 0;
@@ -166,12 +176,61 @@ unsigned Canvas2DLayerBridge::prepareTexture(WebTextureUpdater& updater)
 
 WebGraphicsContext3D* Canvas2DLayerBridge::context()
 {
+    ASSERT(m_context.get());
     return m_context->webContext();
 }
 
+bool Canvas2DLayerBridge::contextIsValid()
+{
+    RefPtr<GraphicsContext3D> sharedContext = SharedGraphicsContext3D::get();
+    if (!sharedContext || sharedContext->webContext()->isContextLost()) {

[danakj, 2013/05/24 17:42:36]

Do you actually see a way to have isContextLost() be true here other than the
context getting lost in between you grabbing it and checking the lost value?

I believe the context should be getting a callback on loss and be invalidating
the ContextProvider as soon as the loss happens. When you call SharedGC3D::get()
and get the ContextProvider (in a WGContextProvider), it should see the loss,
and make a new ContextProvider at that time.

+        // Context was lost since last call to contextIsValid and
+        // SharedGraphicsContext3D has not recovered.
+        m_context.clear();
+        m_layer->clearTexture();
+        return false;
+    }
+    if (m_context != sharedContext) {
+        ASSERT(sharedContext.get());
+        // Old context was lost and sharedContext has recoverred.

[Stephen White, 2013/05/24 17:51:01]

Nit: recovered.

+        // Use the new context to recover the layer
+        m_context = sharedContext;
+        m_layer->clearTexture();
+        GrContext* gr = m_context->grContext();
+        if (gr) {
+            gr->resetContext();
+            SkImage::Info info;
+            info.fWidth = m_canvas->getTopDevice()->width();
+            info.fHeight = m_canvas->getTopDevice()->height();
+            info.fColorType = SkImage::kPMColor_ColorType;
+            info.fAlphaType = SkImage::kPremul_AlphaType;
+            SkAutoTUnref<SkSurface> surface(SkSurface::NewRenderTarget(gr, info));

[Stephen White, 2013/05/24 17:51:01]

This should be refactored with the same code in ImageBuffer (one place or the
other).

+            if (surface.get()) {
+                m_canvas->setSurface(surface.get());
+                // FIXME: draw sad canvas picture into new buffer crbug.com/

[Stephen White, 2013/05/24 17:51:01]

Need bug ID. :)

+            } else {
+                // Surface allocation failed. Reset m_context to trigger subsequent retry
+                m_context.clear();
+                return false;
+            }
+        } else {
+            m_context.clear();
+            return false;
+        }
+#if !ENABLE(CANVAS_USES_MAILBOX)
+        GrRenderTarget* renderTarget = reinterpret_cast<GrRenderTarget*>(m_canvas->getDevice()->accessRenderTarget());
+        if (renderTarget)
+            m_layer->setTextureId(renderTarget->asTexture()->getTextureHandle());
+#endif
+    }
+    return true;
+}
+
 bool Canvas2DLayerBridge::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox)
 {
 #if ENABLE(CANVAS_USES_MAILBOX)
+    if (!m_canvas.get() || !contextIsValid())
+        return false;
     // Release to skia textures that were previouosly released by the
     // compositor. We do this before acquiring the next snapshot in
     // order to cap maximum gpu memory consumption.