Batch multiple single NVPR draw paths to instanced draws

src/gpu/GrPath.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.
  */
 
 #ifndef GrPath_DEFINED
 #define GrPath_DEFINED
 
@@ skipping 18 matching lines @@
 #endif
     {
     }
 
     static void ComputeKey(const SkPath& path, const GrStrokeInfo& stroke, GrUniqueKey* key,
                            bool* outIsVolatile);
 
     const SkRect& getBounds() const { return fBounds; }
 
     GrPathRendering::FillType getFillType() const { return fFillType; }
+
+    /**
+     * Returns true if a path can be drawn in the same draw paths operation as the other
+     * path. Should return true only when the condition holds transitively with all other paths in
+     * the same group.
+     * E.g.
+     * canCombineDrawPathBatchWith(a) AND canCombineDrawPathBatchWith(b)
+     * canCombineDrawPathBatchWith(a) AND canCombineDrawPathBatchWith(c)
+     *  implies
+     * canCombineDrawPathBatchWith(b) AND canCombineDrawPathBatchWith(c)
+     */
+    virtual bool canCombineDrawPathBatchWith(const GrPath& other) const = 0;
 #ifdef SK_DEBUG
     bool isEqualTo(const SkPath& path, const GrStrokeInfo& stroke) const;
 #endif
 
 protected:
     // Subclass should init these.
     SkRect fBounds;
     GrPathRendering::FillType fFillType;
 #ifdef SK_DEBUG
     SkPath fSkPath;
     GrStrokeInfo fStroke;
 #endif
 
 private:
     typedef GrGpuResource INHERITED;
 };
 
 #endif