Add a means of extracting active operations from SkPicture

include/core/SkPicture.h

Index: include/core/SkPicture.h
===================================================================
--- include/core/SkPicture.h	(revision 13766)
+++ include/core/SkPicture.h	(working copy)
@@ -148,6 +148,33 @@
     */
     void endRecording();
 
+    // An OperationList encapsulates a set of operation offsets into the picture byte
+    // stream along with the CTMs needed for those operation.
+    class OperationList : public SkNoncopyable {

[reed1, 2014/03/14 18:28:32]

does this class need to be public? Can it instead be private but declare our
impl as a friend?

[robertphillips, 2014/03/14 18:36:08]

SkPicturePlayback provides the impl and is already a friend. SkGpuDevice needs
to access the information and is pretty far away.

[robertphillips, 2014/03/14 19:23:23]

Done.

+    public:
+        // If valid returns false then there is no optimization data
+        // present. All the draw operations need to be issued.
+        virtual bool valid() const { return false; }
+
+        // The following three entry points should only be accessed if
+        // 'valid' returns true.
+        virtual int numOps() const { SkASSERT(false); return 0; };
+        // The offset in the picture of the operation to execute.
+        virtual uint32_t offset(int index) const { SkASSERT(false); return 0; };
+        // The CTM that must be installed for the operation to behave correctly
+        virtual const SkMatrix& matrix(int index) const { SkASSERT(false); return SkMatrix::I(); }
+
+        static const OperationList& InvalidList();
+
+    private:
+        typedef SkNoncopyable INHERITED;
+    };
+
+    /** PRIVATE / EXPERIMENTAL -- do not call
+        Return the operations required to render the content inside 'queryRect'.
+    */
+    const OperationList& EXPERIMENTAL_getActiveOps(const SkIRect& queryRect);
+
     /** Replays the drawing commands on the specified canvas. This internally
         calls endRecording() if that has not already been called.
         @param canvas the canvas receiving the drawing commands.