[Reland] Repeating SkBitmapProcState rounding bias

src/core/SkBitmapProcState.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapCache.h"
 #include "SkBitmapController.h"
 #include "SkBitmapProcState.h"
@@ skipping 802 matching lines @@
 
 void  Clamp_S32_opaque_D32_nofilter_DX_shaderproc(const SkBitmapProcState& s, int x, int y,
                                                   SkPMColor* SK_RESTRICT dst, int count) {
     SkASSERT((s.fInvType & ~(SkMatrix::kTranslate_Mask |
                              SkMatrix::kScale_Mask)) == 0);
 
     const unsigned maxX = s.fPixmap.width() - 1;
     SkFractionalInt fx;
     int dstY;
     {
-        SkPoint pt;
-        s.fInvProc(s.fInvMatrix, SkIntToScalar(x) + SK_ScalarHalf, SkIntToScalar(y) + SK_ScalarHalf,
-                   &pt);
-        fx = SkScalarToFractionalInt(pt.fY)
-            + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleY());
+        const SkBitmapProcStateAutoMapper mapper(s, x, y);
         const unsigned maxY = s.fPixmap.height() - 1;
-        dstY = SkClampMax(SkFractionalIntToInt(fx), maxY);
-        fx = SkScalarToFractionalInt(pt.fX)
-            + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleX());
+        dstY = SkClampMax(SkFractionalIntToInt(mapper.y()), maxY);
+        fx = mapper.x();
     }
 
     const SkPMColor* SK_RESTRICT src = s.fPixmap.addr32(0, dstY);
     const SkFractionalInt dx = s.fInvSxFractionalInt;
 
     // Check if we're safely inside [0...maxX] so no need to clamp each computed index.
     //
     if ((uint64_t)SkFractionalIntToInt(fx) <= maxX &&
         (uint64_t)SkFractionalIntToInt(fx + dx * (count - 1)) <= maxX)
     {
@@ skipping 16 matching lines @@
             fx += dx;
         }
     } else {
         for (int i = 0; i < count; ++i) {
             dst[i] = src[SkClampMax(SkFractionalIntToInt(fx), maxX)];
             fx += dx;
         }
     }
 }