Avoid re-rendering stencil clip for every draw with reducable clip stack

src/gpu/GrReducedClip.h

 
 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkClipStack.h"
 #include "SkTLList.h"
 
 namespace GrReducedClip {
 
 typedef SkTLList<SkClipStack::Element> ElementList;
 
 enum InitialState {
     kAllIn_InitialState,
     kAllOut_InitialState,
 };
 
 /**
  * This function takes a clip stack and a query rectangle and it produces a reduced set of
- * SkClipStack::Elements that are equivalent to applying the full stack to the rectangle. The
+ * SkClipStack::Elements that are equivalent to applying the full stack to the rectangle. The clip
+ * stack generation id that represents the list of elements is returned in resultGenID. The
  * initial state of the query rectangle before the first clip element is applied is returned via
  * initialState. Optionally, the caller can request a tighter bounds on the clip be returned via
  * tighterBounds. If not NULL, tighterBounds will always be contained by queryBounds after return.
  * If tighterBounds is specified then it is assumed that the caller will implicitly clip against it.
  * If the caller specifies non-NULL for requiresAA then it will indicate whether anti-aliasing is
  * required to process any of the elements in the result.
  *
  * This may become a member function of SkClipStack when its interface is determined to be stable.
  */
 void ReduceClipStack(const SkClipStack& stack,
                      const SkIRect& queryBounds,
                      ElementList* result,
+                     int32_t* resultGenID,
                      InitialState* initialState,
                      SkIRect* tighterBounds = NULL,
                      bool* requiresAA = NULL);
 
 } // namespace GrReducedClip