allow subpixel positioning w/ bitmap filtering

src/core/SkMatrixUtils.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkMatrixUtils_DEFINED
 #define SkMatrixUtils_DEFINED
 
 #include "SkMatrix.h"
 
 /**
  *  Number of subpixel bits used in skia's bilerp.
  *  See SkBitmapProcState_procs.h and SkBitmapProcState_filter.h
  */
 #define kSkSubPixelBitsForBilerp   4
 
+bool SkRectIsOnGrid(int width, int height, const SkRect& r, unsigned subpixelBits);
+
 /**
  *  Given a matrix and width/height, return true if the computed dst-rect would
  *  align such that there is a 1-to-1 coorspondence between src and dst pixels.
  *  This can be called by drawing code to see if drawBitmap can be turned into
  *  drawSprite (which is faster).
  *
  *  The src-rect is defined to be { 0, 0, width, height }
  *
  *  The "closeness" test is based on the subpixelBits parameter. Pass 0 for
  *  round-to-nearest behavior (e.g. nearest neighbor sampling). Pass the number
@@ skipping 16 matching lines @@
     followed by another rotation. If there is a reflection, one of the scale
     factors will be negative.
     Returns true if successful. Returns false if the matrix is degenerate.
     */
 bool SkDecomposeUpper2x2(const SkMatrix& matrix,
                          SkPoint* rotation1,
                          SkPoint* scale,
                          SkPoint* rotation2);
 
 #endif