Repeating SkBitmapProcState rounding bias

src/core/SkBitmapProcState.cpp

Index: src/core/SkBitmapProcState.cpp
diff --git a/src/core/SkBitmapProcState.cpp b/src/core/SkBitmapProcState.cpp
index 487bd80402609f454b894e5e124eb5d8eb20c9eb..b08db53ffa2f582a89587bea5dc2475e410cd685 100644
--- a/src/core/SkBitmapProcState.cpp
+++ b/src/core/SkBitmapProcState.cpp
@@ -195,6 +195,15 @@ bool SkBitmapProcState::chooseProcs(const SkMatrix& inv, const SkPaint& paint) {
     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!
 
@@ -823,12 +832,10 @@ void  Clamp_S32_opaque_D32_nofilter_DX_shaderproc(const SkBitmapProcState& s, in
         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);