change SkCanvasStack to take ownership of its subcanvases

Inspired by https://bugs.chromium.org/p/chromium/issues/detail?id=663959

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4799

Change-Id: I69f7ac73386bb7ca96778e2fec4cb2757b982a52
Reviewed-on: https://skia-review.googlesource.com/4799
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/utils/SkCanvasStack.h b/src/utils/SkCanvasStack.h
index 762ab9f76f..0e6e4b6381 100644
--- a/src/utils/SkCanvasStack.h
+++ b/src/utils/SkCanvasStack.h
@@ -11,12 +11,18 @@
 #include "SkNWayCanvas.h"
 #include "SkTArray.h"
 
+/**
+ *  Like NWayCanvas, in that it forwards all canvas methods to each sub-canvas that is "pushed".
+ *
+ *  Unlike NWayCanvas, this takes ownership of each subcanvas, and deletes them when this canvas
+ *  is deleted.
+ */
 class SkCanvasStack : public SkNWayCanvas {
 public:
     SkCanvasStack(int width, int height);
     virtual ~SkCanvasStack();
 
-    void pushCanvas(SkCanvas* canvas, const SkIPoint& origin);
+    void pushCanvas(std::unique_ptr<SkCanvas>, const SkIPoint& origin);
     void removeAll() override;
 
     /*
@@ -42,6 +48,7 @@ private:
     struct CanvasData {
         SkIPoint origin;
         SkRegion requiredClip;
+        std::unique_ptr<SkCanvas> ownedCanvas;
     };
 
     SkTArray<CanvasData> fCanvasData;