Sync canvas proxy CTM (b/21945972)

SkiaCanvasProxy was being created with an identity transform, ignoring
any transform that may have been applied in Java (or C++) to the
android graphics Canvas it was proxy for. This CL makes sure the
DisplayListCanvas transform is propagated to the Proxy every time
asSkCanvas() is called.

We could instead move the code to the SkiaCanvasProxy constructor
if we got rid of the cached proxy on DisplayListCanvas; nobody's
using the proxy heavily enough that that should be a performance
hit at this time.

BUG:21945972
R=djsollen@google.com

Change-Id: I99ed1563802a2449bb9939cb67976cd60dd8611c

2 files changed, 12 insertions, 0 deletions

diff --git a/libs/hwui/Canvas.h b/libs/hwui/Canvas.h
index aa24673..562bb80 100644
--- a/libs/hwui/Canvas.h
+++ b/libs/hwui/Canvas.h
@@ -47,6 +47,10 @@ public:
      *  It is useful for testing and clients (e.g. Picture/Movie) that expect to
      *  draw their contents into an SkCanvas.
      *
+     *  The SkCanvas returned is *only* valid until another Canvas call is made
+     *  that would change state (e.g. matrix or clip). Clients of asSkCanvas()
+     *  are responsible for *not* persisting this pointer.
+     *
      *  Further, the returned SkCanvas should NOT be unref'd and is valid until
      *  this canvas is destroyed or a new bitmap is set.
      */
diff --git a/libs/hwui/DisplayListCanvas.cpp b/libs/hwui/DisplayListCanvas.cpp
index 843c412..1988f5e 100644
--- a/libs/hwui/DisplayListCanvas.cpp
+++ b/libs/hwui/DisplayListCanvas.cpp
@@ -99,6 +99,14 @@ SkCanvas* DisplayListCanvas::asSkCanvas() {
     if (!mSkiaCanvasProxy) {
         mSkiaCanvasProxy.reset(new SkiaCanvasProxy(this));
     }
+
+    // SkCanvas instances default to identity transform, but should inherit
+    // the state of this Canvas; if this code was in the SkiaCanvasProxy
+    // constructor, we couldn't cache mSkiaCanvasProxy.
+    SkMatrix parentTransform;
+    getMatrix(&parentTransform);
+    mSkiaCanvasProxy.get()->setMatrix(parentTransform);
+
     return mSkiaCanvasProxy.get();
 }