Fixing Canvas2DLayerBridge to handle lost graphics contexts

Source/core/platform/graphics/skia/ImageBufferSkia.cpp

Index: Source/core/platform/graphics/skia/ImageBufferSkia.cpp
diff --git a/Source/core/platform/graphics/skia/ImageBufferSkia.cpp b/Source/core/platform/graphics/skia/ImageBufferSkia.cpp
index 69464c730bc365519ba91d864583d131be64a74c..593498905f3a199d103c3288145aea0eb981b5b7 100644
--- a/Source/core/platform/graphics/skia/ImageBufferSkia.cpp
+++ b/Source/core/platform/graphics/skia/ImageBufferSkia.cpp
@@ -193,6 +193,13 @@ GraphicsContext* ImageBuffer::context() const
     return m_context.get();
 }
 
+static bool contextIsValid(const ImageBufferData* data)

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

I think this should be ImageBuffer::isValid(), and take no args.

+{
+    if (data->m_layerBridge)
+        return const_cast<Canvas2DLayerBridge*>(data->m_layerBridge.get())->contextIsValid();
+    return true;
+}
+
 static SkBitmap deepSkBitmapCopy(const SkBitmap& bitmap)
 {
     SkBitmap tmp;
@@ -204,9 +211,12 @@ static SkBitmap deepSkBitmapCopy(const SkBitmap& bitmap)
 
 PassRefPtr<Image> ImageBuffer::copyImage(BackingStoreCopy copyBehavior, ScaleBehavior) const
 {
-    const SkBitmap& bitmap = *context()->bitmap();
-    // FIXME: Start honoring ScaleBehavior to scale 2x buffers down to 1x.
-    return BitmapImage::create(NativeImageSkia::create(copyBehavior == CopyBackingStore ? deepSkBitmapCopy(bitmap) : bitmap, m_resolutionScale));
+    if (contextIsValid(&m_data)) {

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

Since this is the exceptional state, this should be the early-return.

I.e.,

if (!isValid())
    return BitmapImage::create(NativeImageSkia::create());

+        const SkBitmap& bitmap = *context()->bitmap();
+        // FIXME: Start honoring ScaleBehavior to scale 2x buffers down to 1x.
+        return BitmapImage::create(NativeImageSkia::create(copyBehavior == CopyBackingStore ? deepSkBitmapCopy(bitmap) : bitmap, m_resolutionScale));
+    }
+    return BitmapImage::create(NativeImageSkia::create());
 }
 
 BackingStoreCopy ImageBuffer::fastCopyImageMode()
@@ -221,7 +231,7 @@ PlatformLayer* ImageBuffer::platformLayer() const
 
 bool ImageBuffer::copyToPlatformTexture(GraphicsContext3D& context, Platform3DObject texture, GC3Denum internalFormat, GC3Denum destType, GC3Dint level, bool premultiplyAlpha, bool flipY)
 {
-    if (!m_data.m_layerBridge || !platformLayer())
+    if (!m_data.m_layerBridge || !platformLayer() || !contextIsValid(&m_data))
         return false;
 
     Platform3DObject sourceTexture = m_data.m_layerBridge->backBufferTexture();
@@ -261,23 +271,27 @@ static bool drawNeedsCopy(GraphicsContext* src, GraphicsContext* dst)
 void ImageBuffer::draw(GraphicsContext* context, ColorSpace styleColorSpace, const FloatRect& destRect, const FloatRect& srcRect,
     CompositeOperator op, BlendMode blendMode, bool useLowQualityScale)
 {
-    const SkBitmap& bitmap = *m_context->bitmap();
-    RefPtr<Image> image = BitmapImage::create(NativeImageSkia::create(drawNeedsCopy(m_context.get(), context) ? deepSkBitmapCopy(bitmap) : bitmap));
-    context->drawImage(image.get(), styleColorSpace, destRect, srcRect, op, blendMode, DoNotRespectImageOrientation, useLowQualityScale);
+    if (contextIsValid(&m_data)) {

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

Same here:

if (!isValid())
    return;

+        const SkBitmap& bitmap = *m_context->bitmap();
+        RefPtr<Image> image = BitmapImage::create(NativeImageSkia::create(drawNeedsCopy(m_context.get(), context) ? deepSkBitmapCopy(bitmap) : bitmap));
+        context->drawImage(image.get(), styleColorSpace, destRect, srcRect, op, blendMode, DoNotRespectImageOrientation, useLowQualityScale);
+    }
 }
 
 void ImageBuffer::drawPattern(GraphicsContext* context, const FloatRect& srcRect, const AffineTransform& patternTransform,
                               const FloatPoint& phase, ColorSpace styleColorSpace, CompositeOperator op, const FloatRect& destRect)
 {
-    const SkBitmap& bitmap = *m_context->bitmap();
-    RefPtr<Image> image = BitmapImage::create(NativeImageSkia::create(drawNeedsCopy(m_context.get(), context) ? deepSkBitmapCopy(bitmap) : bitmap));
-    image->drawPattern(context, srcRect, patternTransform, phase, styleColorSpace, op, destRect);
+    if (contextIsValid(&m_data)) {

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

Same here (and more places below; I'll stop nagging now).

+        const SkBitmap& bitmap = *m_context->bitmap();
+        RefPtr<Image> image = BitmapImage::create(NativeImageSkia::create(drawNeedsCopy(m_context.get(), context) ? deepSkBitmapCopy(bitmap) : bitmap));
+        image->drawPattern(context, srcRect, patternTransform, phase, styleColorSpace, op, destRect);
+    }
 }
 
 void ImageBuffer::platformTransformColorSpace(const Vector<int>& lookUpTable)
 {
     // FIXME: Disable color space conversions on accelerated canvases (for now).
-    if (context()->isAccelerated())
+    if (context()->isAccelerated() || !contextIsValid(&m_data))
         return;
 
     const SkBitmap& bitmap = *context()->bitmap();
@@ -332,16 +346,25 @@ PassRefPtr<Uint8ClampedArray> getImageData(const IntRect& rect, GraphicsContext*
 
 PassRefPtr<Uint8ClampedArray> ImageBuffer::getUnmultipliedImageData(const IntRect& rect, CoordinateSystem) const
 {
-    return getImageData<Unmultiplied>(rect, context(), m_size);
+    if (contextIsValid(&m_data))
+        return getImageData<Unmultiplied>(rect, context(), m_size);
+    RefPtr<Uint8ClampedArray> result = Uint8ClampedArray::create(rect.width() * rect.height() * 4);
+    return result.release();
 }
 
 PassRefPtr<Uint8ClampedArray> ImageBuffer::getPremultipliedImageData(const IntRect& rect, CoordinateSystem) const
 {
-    return getImageData<Premultiplied>(rect, context(), m_size);
+    if (contextIsValid(&m_data))
+        return getImageData<Premultiplied>(rect, context(), m_size);
+    RefPtr<Uint8ClampedArray> result = Uint8ClampedArray::create(rect.width() * rect.height() * 4);
+    return result.release();
 }
 
 void ImageBuffer::putByteArray(Multiply multiplied, Uint8ClampedArray* source, const IntSize& sourceSize, const IntRect& sourceRect, const IntPoint& destPoint, CoordinateSystem)
 {
+    if (!contextIsValid(&m_data))
+        return;
+
     ASSERT(sourceRect.width() > 0);
     ASSERT(sourceRect.height() > 0);
 
@@ -412,12 +435,13 @@ String ImageBuffer::toDataURL(const String& mimeType, const double* quality, Coo
 {
     ASSERT(MIMETypeRegistry::isSupportedImageMIMETypeForEncoding(mimeType));
 
-    Vector<char> encodedImage;
-    if (!encodeImage(*context()->bitmap(), mimeType, quality, &encodedImage))
-        return "data:,";
-
     Vector<char> base64Data;
-    base64Encode(encodedImage, base64Data);
+    if (contextIsValid(&m_data)) {
+        Vector<char> encodedImage;
+        if (!encodeImage(*context()->bitmap(), mimeType, quality, &encodedImage))
+            return "data:,";
+        base64Encode(encodedImage, base64Data);
+    }
 
     return "data:" + mimeType + ";base64," + base64Data;
 }