Determine if OffscreenCanvas is paintable in different rendering contexts

third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp

Index: third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp
diff --git a/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp
index 0585db0a307aec55af413181a0509c43cd695ced..b33456de79c200a46fac37d6704608d60be575f0 100644
--- a/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp
+++ b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp
@@ -6,7 +6,10 @@
 
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/offscreencanvas/OffscreenCanvas.h"
+#include "modules/imagebitmap/ImageBitmapRenderingContext.h"
 #include "modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h"
+#include "modules/webgl/WebGLRenderingContextBase.h"
+#include "platform/graphics/ImageBuffer.h"
 
 namespace blink {
 
@@ -22,4 +25,21 @@ void OffscreenCanvasModules::getContext(ScriptState* scriptState, OffscreenCanva
         context->setOffscreenCanvasGetContextResult(result);
 }
 
+bool OffscreenCanvasModules::isPaintable(OffscreenCanvas& offscreenCanvas)

[Justin Novosad, 2016/08/19 14:55:47]

There is a cleaner way to implement this: put a pure virtual method
isPaintable() on CanvasRenderingContext.  It will allow you to keep
drawingBuffer() encapsulated in WebGLRenderingContextBase, and it will allow you
to implement isPaintable in core (in OffscreenCanvas proper), and it avoid
sticking explicit knowledge of all the context types in OffscreenCAnvas, which
is better for maintainability.

+{
+    CanvasRenderingContext* context = offscreenCanvas.renderingContext();
+    if (!context)
+        return ImageBuffer::canCreateImageBuffer(offscreenCanvas.size());
+
+    if (context->is2d())
+        return toOffscreenCanvasRenderingContext2D(context)->imageBuffer();
+    if (context->is3d())
+        return toWebGLRenderingContextBase(context)->drawingBuffer();
+    if (context->getContextType() == CanvasRenderingContext::ContextImageBitmap)
+        return toImageBitmapRenderingContext(context)->image();
+
+    NOTREACHED();
+    return false;
+}
+
 } // namespace blink