add SkMatrix::decomposeScale

include/core/SkMatrix.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkMatrix_DEFINED
@@ skipping 606 matching lines @@
     SkScalar getMaxScale() const;
 
     /**
      * Gets both the min and max scale factors. The min scale factor is scaleFactors[0] and the max
      * is scaleFactors[1]. If the matrix has perspective false will be returned and scaleFactors
      * will be unchanged.
      */
     bool getMinMaxScales(SkScalar scaleFactors[2]) const;
 
     /**
+     *  Attempt to decompose this matrix into a scale-only component and whatever remains, where
+     *  the scale component is to be applied first.
+     *
+     *  M -> Remaining * Scale
+     *
+     *  On success, return true and assign the scale and remaining components (assuming their
+     *  respective parameters are not null). On failure return false and ignore the parameters.
+     *
+     *  Possible reasons to fail: perspective, one or more scale factors are zero.
+     */
+    bool decomposeScale(SkSize* scale, SkMatrix* remaining = NULL) const;
+
+    /**
      *  Return a reference to a const identity matrix
      */
     static const SkMatrix& I();
 
     /**
      *  Return a reference to a const matrix that is "invalid", one that could
      *  never be used.
      */
     static const SkMatrix& InvalidMatrix();
 
@@ skipping 134 matching lines @@
     static void RotTrans_pts(const SkMatrix&, SkPoint dst[], const SkPoint[],
                              int count);
     static void Persp_pts(const SkMatrix&, SkPoint dst[], const SkPoint[], int);
 
     static const MapPtsProc gMapPtsProcs[];
 
     friend class SkPerspIter;
 };
 
 #endif