Use SkBitmapProcStateAutoMapper for filter samplers also

Observation: filter procs are also biased by s.fFilterOne{X,Y} / 2.  They all do
something along these lines:

  s.fInvProc(s.fInvMatrix,
    SkIntToScalar(x) + SK_ScalarHalf,
    SkIntToScalar(y) + SK_ScalarHalf, &srcPt);

  SkFixed fx = SkScalarToFixed(srcPt.fX) - (s.fFilterOneX >> 1);
  SkFixed fy = SkScalarToFixed(srcPt.fY) - (s.fFilterOneX >> 1);

It's trivial to extend SkBitmapProcStateAutoMapper to handle this internally, and
convert everyone off explicit mapping.

R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1661613002
CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review URL: https://codereview.chromium.org/1661613002

1 files changed, 13 insertions, 7 deletions

diff --git a/src/core/SkBitmapProcState.h b/src/core/SkBitmapProcState.h
index 0ae8cf2856..fca7dc0a3e 100644
--- a/src/core/SkBitmapProcState.h
+++ b/src/core/SkBitmapProcState.h
@@ -189,7 +189,6 @@ void ClampX_ClampY_nofilter_affine(const SkBitmapProcState& s,
                                    uint32_t xy[], int count, int x, int y);
 
 // Helper class for mapping the middle of pixel (x, y) into SkFractionalInt bitmap space.
-// TODO: filtered version which applies a fFilterOne{X,Y}/2 bias instead of epsilon?
 class SkBitmapProcStateAutoMapper {
 public:
     SkBitmapProcStateAutoMapper(const SkBitmapProcState& s, int x, int y,
@@ -199,12 +198,19 @@ public:
                    SkIntToScalar(x) + SK_ScalarHalf,
                    SkIntToScalar(y) + SK_ScalarHalf, &pt);
 
-        // SkFixed epsilon bias to ensure inverse-mapped bitmap coordinates are rounded
-        // consistently WRT geometry.  Note that we only need the bias for positive scales:
-        // for negative scales, the rounding is intrinsically correct.
-        // We scale it to persist SkFractionalInt -> SkFixed conversions.
-        const SkFixed biasX = (s.fInvMatrix.getScaleX() > 0);
-        const SkFixed biasY = (s.fInvMatrix.getScaleY() > 0);
+        SkFixed biasX, biasY;
+        if (s.fFilterLevel == kNone_SkFilterQuality) {
+            // SkFixed epsilon bias to ensure inverse-mapped bitmap coordinates are rounded
+            // consistently WRT geometry.  Note that we only need the bias for positive scales:
+            // for negative scales, the rounding is intrinsically correct.
+            // We scale it to persist SkFractionalInt -> SkFixed conversions.
+            biasX = (s.fInvMatrix.getScaleX() > 0);
+            biasY = (s.fInvMatrix.getScaleY() > 0);
+        } else {
+            biasX = s.fFilterOneX >> 1;
+            biasY = s.fFilterOneY >> 1;
+        }
+
         fX = SkScalarToFractionalInt(pt.x()) - SkFixedToFractionalInt(biasX);
         fY = SkScalarToFractionalInt(pt.y()) - SkFixedToFractionalInt(biasY);