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..6b3d6f0e42595dc594b357a2b0805b088ce1d3be 100644
--- a/sky/engine/core/painting/Canvas.h
+++ b/sky/engine/core/painting/Canvas.h
@@ -8,6 +8,7 @@
 #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 +16,30 @@
 #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(PassRefPtr<PictureRecorder> recorder,

[abarth-chromium, 2015/06/23 02:28:44]

I think what Eric is saying is that ideally |PassRefPtr<PictureRecorder>| would
be |PictureRecorder*| because we're not going to keep a reference to the
|PictureRecorder|.  It's possible that doesn't compile because of the IDL code
generator, in which case what you've got here is fine.

[iansf, 2015/06/23 22:46:09]

Confirmed that |PictureRecorder*| works, and updated accordingly.

+                                     double width,
+                                     double height) {
+        ASSERT(recorder);
+        PassRefPtr<Canvas> canvas = create(
+            recorder->beginRecording(width, height));
+        recorder->set_canvas(canvas.get());

[eseidel, 2015/06/23 00:41:32]

Who keeps the PictureRecorder alive? , Typically accepting a PassRefPtr<> means
that you're taking ownership of the object, or at least you're comfortable being
the last ref of said object. :)  It looks like this code may depend on someone
else holding onto the PictureRecorder?

[abarth-chromium, 2015/06/23 02:28:44]

Canvas effectively has a weak reference to the picture recorder.  We don't
actually use a base::WeakPtr because that would add overhead to every draw call.
 Instead, the PictureRecorder notifies the Canvas when it dies, which makes the
Canvas object ignore all subsequent draw calls.

+        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 +69,16 @@ public:
                    const Paint* paint);
 
     SkCanvas* skCanvas() { return m_canvas; }
+    void clearSkCanvas() { m_canvas = nullptr; }
+    bool isRecording() const { return m_canvas != nullptr; }

[eseidel, 2015/06/23 00:41:32]

!!m_canvas works too.  This is fine though. :)

[iansf, 2015/06/23 22:46:09]

Acknowledged.

 
 protected:
-    PassRefPtr<DisplayList> finishRecording();
-
-    bool isRecording() const { return m_canvas; }
+    Canvas(SkCanvas* skCanvas);

[abarth-chromium, 2015/06/23 02:28:44]

Please mark one-argument constructors |explicit|.

[iansf, 2015/06/23 22:46:09]

Done.

 
 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.

[abarth-chromium, 2015/06/23 02:28:44]

@eseidel: Here's the comment that's intended to answer your question.

     SkCanvas* m_canvas;
 };