Decouple Canvas from DisplayList and map Picture and PictureRecorder more directly to their Skia co…

sky/engine/core/painting/Canvas.h

Index: sky/engine/core/painting/Canvas.h
diff --git a/sky/engine/core/painting/Canvas.h b/sky/engine/core/painting/Canvas.h
index abd325643ec8188ffcf6a0feb467d3ef19f0d020..00c6779269f681cb983d4669f295de1afb0ebb86 100644
--- a/sky/engine/core/painting/Canvas.h
+++ b/sky/engine/core/painting/Canvas.h
@@ -5,9 +5,11 @@
 #ifndef SKY_ENGINE_CORE_PAINTING_CANVAS_H_
 #define SKY_ENGINE_CORE_PAINTING_CANVAS_H_
 
+#include "sky/engine/bindings/exception_state.h"
 #include "sky/engine/core/painting/CanvasPath.h"
 #include "sky/engine/core/painting/Paint.h"
 #include "sky/engine/core/painting/Picture.h"
+#include "sky/engine/core/painting/PictureRecorder.h"
 #include "sky/engine/core/painting/RRect.h"
 #include "sky/engine/core/painting/Rect.h"
 #include "sky/engine/platform/graphics/DisplayList.h"
@@ -15,21 +17,43 @@
 #include "sky/engine/tonic/float32_list.h"
 #include "sky/engine/wtf/PassRefPtr.h"
 #include "sky/engine/wtf/RefCounted.h"
+#include "third_party/skia/include/core/SkCanvas.h"
 
 namespace blink {
-class Element;
 class CanvasImage;
 
 class Canvas : public RefCounted<Canvas>, public DartWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    Canvas(const FloatSize& size);
-    ~Canvas() override;
+    static PassRefPtr<Canvas> create(SkCanvas* skCanvas) {
+        ASSERT(skCanvas);
+        return adoptRef(new Canvas(skCanvas));
+    }
+
+    static PassRefPtr<Canvas> create(PictureRecorder* recorder,
+                                     double width,
+                                     double height,
+                                     ExceptionState& es) {
+        ASSERT(recorder);
+        if (recorder->isRecording()) {
+            es.ThrowTypeError(
+                "You must call PictureRecorder.endRecording() before reusing a"
+                " PictureRecorder to create a new Canvas object.");
+            // TODO(iansf): We should return a nullptr here, I think, but doing
+            //              so will require modifying the dart template code to
+            //              to correctly handle constructors that throw
+            //              exceptions.  For now, just let it return a dart
+            //              object that may cause a crash later on -- if the
+            //              dart code catches the error, it will leak a canvas
+            //              but it won't crash.
+        }
+        PassRefPtr<Canvas> canvas = create(
+            recorder->beginRecording(width, height));
+        recorder->set_canvas(canvas.get());
+        return canvas;
+    }
 
-    // Width/Height define a culling rect which Skia may use for optimizing
-    // out draw calls issued outside the rect.
-    float width() const { return m_size.width(); }
-    float height() const { return m_size.height(); }
+    ~Canvas() override;
 
     void save();
     void saveLayer(const Rect& bounds, const Paint* paint = nullptr);
@@ -59,15 +83,16 @@ public:
                    const Paint* paint);
 
     SkCanvas* skCanvas() { return m_canvas; }
+    void clearSkCanvas() { m_canvas = nullptr; }
+    bool isRecording() const { return !!m_canvas; }
 
 protected:
-    PassRefPtr<DisplayList> finishRecording();
-
-    bool isRecording() const { return m_canvas; }
+    explicit Canvas(SkCanvas* skCanvas);
 
 private:
-    FloatSize m_size;
-    RefPtr<DisplayList> m_displayList;
+    // The SkCanvas is supplied by a call to SkPictureRecorder::beginRecording,
+    // which does not transfer ownership.  For this reason, we hold a raw
+    // pointer and manually set the SkCanvas to null in clearSkCanvas.
     SkCanvas* m_canvas;
 };