SkBitmapProcState rounding bias

src/core/SkBitmapProcState_matrix.h

 
 /*
  * 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 "SkMath.h"
 #include "SkMathPriv.h"
@@ skipping 46 matching lines @@
 
     const unsigned maxX = s.fPixmap.width() - 1;
     const SkFixed one = s.fFilterOneX;
     const SkFractionalInt dx = s.fInvSxFractionalInt;
     SkFractionalInt fx;
 
     {
         SkPoint pt;
         s.fInvProc(s.fInvMatrix, SkIntToScalar(x) + SK_ScalarHalf,
                                   SkIntToScalar(y) + SK_ScalarHalf, &pt);
-        const SkFixed fy = SkScalarToFixed(pt.fY) - (s.fFilterOneY >> 1);
+        const SkFixed fy = SkScalarToFixed(pt.fY) - (s.fFilterOneY >> 1)
+            + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleY());
         const unsigned maxY = s.fPixmap.height() - 1;
         // compute our two Y values up front
         *xy++ = PACK_FILTER_Y_NAME(fy, maxY, s.fFilterOneY PREAMBLE_ARG_Y);
         // now initialize fx
-        fx = SkScalarToFractionalInt(pt.fX) - (SkFixedToFractionalInt(one) >> 1);
+        fx = SkScalarToFractionalInt(pt.fX) - (SkFixedToFractionalInt(one) >> 1)
+            + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleX());
     }
 
 #ifdef CHECK_FOR_DECAL
     if (can_truncate_to_fixed_for_decal(fx, dx, count, maxX)) {
         decal_filter_scale(xy, SkFractionalIntToFixed(fx),
                            SkFractionalIntToFixed(dx), count);
     } else
 #endif
     {
         do {
@@ skipping 12 matching lines @@
                              SkMatrix::kAffine_Mask)) == 0);
 
     PREAMBLE(s);
     SkPoint srcPt;
     s.fInvProc(s.fInvMatrix,
                SkIntToScalar(x) + SK_ScalarHalf,
                SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
 
     SkFixed oneX = s.fFilterOneX;
     SkFixed oneY = s.fFilterOneY;
-    SkFixed fx = SkScalarToFixed(srcPt.fX) - (oneX >> 1);
-    SkFixed fy = SkScalarToFixed(srcPt.fY) - (oneY >> 1);
+    SkFixed fx = SkScalarToFixed(srcPt.fX) - (oneX >> 1)
+        + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleX());
+    SkFixed fy = SkScalarToFixed(srcPt.fY) - (oneY >> 1)
+        + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleY());
     SkFixed dx = s.fInvSx;
     SkFixed dy = s.fInvKy;
     unsigned maxX = s.fPixmap.width() - 1;
     unsigned maxY = s.fPixmap.height() - 1;
 
     do {
         *xy++ = PACK_FILTER_Y_NAME(fy, maxY, oneY PREAMBLE_ARG_Y);
         fy += dy;
         *xy++ = PACK_FILTER_X_NAME(fx, maxX, oneX PREAMBLE_ARG_X);
         fx += dx;
@@ skipping 39 matching lines @@
 #undef PERSP_FILTER_NAME
 
 #undef PREAMBLE
 #undef PREAMBLE_PARAM_X
 #undef PREAMBLE_PARAM_Y
 #undef PREAMBLE_ARG_X
 #undef PREAMBLE_ARG_Y
 
 #undef TILEX_LOW_BITS
 #undef TILEY_LOW_BITS