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 177 matching lines @@
     fInvKy          = SkScalarToFixed(fInvMatrix.getSkewY());
     fInvKyFractionalInt = SkScalarToFractionalInt(fInvMatrix.getSkewY());
 
     fAlphaScale = SkAlpha255To256(paint.getAlpha());
 
     fShaderProc32 = nullptr;
     fShaderProc16 = nullptr;
     fSampleProc32 = nullptr;
     fSampleProc16 = nullptr;
 
+#ifndef SK_SUPPORT_LEGACY_BITMAP_SAMPLER_BIAS
+    // We only need a bias when the scale is positive: for negative scales
+    // we're rounding in the right direction intrinsically.
+    fInvBiasX = -(fInvMatrix.getScaleX() > 0);
+    fInvBiasY = -(fInvMatrix.getScaleY() > 0);
+#else
+    fInvBiasX = fInvBiasY = 0;
+#endif
+
     // recompute the triviality of the matrix here because we may have
     // changed it!
 
     trivialMatrix = (fInvMatrix.getType() & ~SkMatrix::kTranslate_Mask) == 0;
 
     if (kLow_SkFilterQuality == fFilterLevel) {
         // Only try bilerp if the matrix is "interesting" and
         // the image has a suitable size.
 
         if (fInvType <= SkMatrix::kTranslate_Mask ||
@@ skipping 608 matching lines @@
     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());
+        fx = SkScalarToFractionalInt(pt.fY) + SkFixedToFractionalInt(s.fInvBiasY);
         const unsigned maxY = s.fPixmap.height() - 1;
         dstY = SkClampMax(SkFractionalIntToInt(fx), maxY);
-        fx = SkScalarToFractionalInt(pt.fX)
-            + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleX());
+        fx = SkScalarToFractionalInt(pt.fX) + SkFixedToFractionalInt(s.fInvBiasX);
     }
 
     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;
         }
     }
 }