Repeating SkBitmapProcState rounding bias

Observe the bias in repeat matrix procs also.

Introduce a utility class to handle device space -> bitmap space
mapping.

BUG=skia:4680,skia:4649
R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1529833003

Review URL: https://codereview.chromium.org/1529833003

4 files changed, 44 insertions, 48 deletions

diff --git a/src/core/SkBitmapProcState.cpp b/src/core/SkBitmapProcState.cpp
index c85a5fb992..1ec47fb602 100644
--- a/src/core/SkBitmapProcState.cpp
+++ b/src/core/SkBitmapProcState.cpp
@@ -824,15 +824,10 @@ void  Clamp_S32_opaque_D32_nofilter_DX_shaderproc(const void* sIn, int x, int y,
     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(SkFixedFloorToInt(mapper.y()), maxY);
+        fx = SkFixedToFractionalInt(mapper.x());
     }
 
     const SkPMColor* SK_RESTRICT src = s.fPixmap.addr32(0, dstY);
@@ -868,4 +863,3 @@ void  Clamp_S32_opaque_D32_nofilter_DX_shaderproc(const void* sIn, int x, int y,
         }
     }
 }
-
diff --git a/src/core/SkBitmapProcState.h b/src/core/SkBitmapProcState.h
index 4d7e7f32dc..bd2a344eca 100644
--- a/src/core/SkBitmapProcState.h
+++ b/src/core/SkBitmapProcState.h
@@ -25,17 +25,6 @@ typedef SkFixed3232    SkFractionalInt;
 #define SkFixedToFractionalInt(x)   SkFixedToFixed3232(x)
 #define SkFractionalIntToInt(x)     SkFixed3232ToInt(x)
 
-// Applying a fixed point (SkFixed, SkFractionalInt) epsilon bias ensures that the inverse-mapped
-// bitmap coordinates are rounded consistently WRT geometry.  Note that we only have to do this
-// when the scale is positive - for negative scales we're already rounding in the right direction.
-static inline int bitmap_sampler_inv_bias(SkScalar scale) {
-#ifndef SK_SUPPORT_LEGACY_BITMAP_SAMPLER_BIAS
-    return -(scale > 0);
-#else
-    return 0;
-#endif
-}
-
 class SkPaint;
 
 struct SkBitmapProcState {
@@ -210,4 +199,32 @@ void S32_D16_filter_DX(const SkBitmapProcState& s,
 void S32_D16_filter_DXDY(const SkBitmapProcState& s,
                          const uint32_t* xy, int count, uint16_t* colors);
 
+// Helper class for mapping the middle of pixel (x, y) into SkFixed bitmap space.
+class SkBitmapProcStateAutoMapper {
+public:
+    SkBitmapProcStateAutoMapper(const SkBitmapProcState& s, int x, int y) {
+        SkPoint pt;
+        s.fInvProc(s.fInvMatrix,
+                   SkIntToScalar(x) + SK_ScalarHalf,
+                   SkIntToScalar(y) + SK_ScalarHalf, &pt);
+
+#ifndef SK_SUPPORT_LEGACY_BITMAP_SAMPLER_BIAS
+        // 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.
+        fX = SkScalarToFixed(pt.x()) - (s.fInvMatrix.getScaleX() > 0);
+        fY = SkScalarToFixed(pt.y()) - (s.fInvMatrix.getScaleY() > 0);
+#else
+        fX = SkScalarToFixed(pt.x());
+        fY = SkScalarToFixed(pt.y());
+#endif
+    }
+
+    SkFixed x() const { return fX; }
+    SkFixed y() const { return fY; }
+
+private:
+    SkFixed fX, fY;
+};
+
 #endif
diff --git a/src/core/SkBitmapProcState_matrix.h b/src/core/SkBitmapProcState_matrix.h
index 42a5ab6e22..e4212b60fe 100644
--- a/src/core/SkBitmapProcState_matrix.h
+++ b/src/core/SkBitmapProcState_matrix.h
@@ -61,17 +61,13 @@ void SCALE_FILTER_NAME(const SkBitmapProcState& s,
     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)
-            + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleY());
+        const SkBitmapProcStateAutoMapper mapper(s, x ,y);
+        const SkFixed fy = mapper.y() - (s.fFilterOneY >> 1);
         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)
-            + bitmap_sampler_inv_bias(s.fInvMatrix.getScaleX());
+        fx = SkFixedToFractionalInt(mapper.x() - (one >> 1));
     }
 
 #ifdef CHECK_FOR_DECAL
@@ -97,17 +93,12 @@ void AFFINE_FILTER_NAME(const SkBitmapProcState& s,
                              SkMatrix::kAffine_Mask)) == 0);
 
     PREAMBLE(s);
-    SkPoint srcPt;
-    s.fInvProc(s.fInvMatrix,
-               SkIntToScalar(x) + SK_ScalarHalf,
-               SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
+    const SkBitmapProcStateAutoMapper mapper(s, x ,y);
 
     SkFixed oneX = s.fFilterOneX;
     SkFixed oneY = s.fFilterOneY;
-    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 fx = mapper.x() - (oneX >> 1);
+    SkFixed fy = mapper.y() - (oneY >> 1);
     SkFixed dx = s.fInvSx;
     SkFixed dy = s.fInvKy;
     unsigned maxX = s.fPixmap.width() - 1;
diff --git a/src/core/SkBitmapProcState_matrix_template.h b/src/core/SkBitmapProcState_matrix_template.h
index 468013c30d..9d639b8a04 100644
--- a/src/core/SkBitmapProcState_matrix_template.h
+++ b/src/core/SkBitmapProcState_matrix_template.h
@@ -22,13 +22,10 @@ void NoFilterProc_Scale(const SkBitmapProcState& s, uint32_t xy[],
     const unsigned maxX = s.fPixmap.width() - 1;
     SkFractionalInt fx;
     {
-        SkPoint pt;
-        s.fInvProc(s.fInvMatrix, SkIntToScalar(x) + SK_ScalarHalf,
-                                  SkIntToScalar(y) + SK_ScalarHalf, &pt);
-        fx = SkScalarToFractionalInt(pt.fY);
+        const SkBitmapProcStateAutoMapper mapper(s, x ,y);
         const unsigned maxY = s.fPixmap.height() - 1;
-        *xy++ = TileProc::Y(s, SkFractionalIntToFixed(fx), maxY);
-        fx = SkScalarToFractionalInt(pt.fX);
+        *xy++ = TileProc::Y(s, mapper.y(), maxY);
+        fx = SkFixedToFractionalInt(mapper.x());
     }
 
     if (0 == maxX) {
@@ -80,13 +77,9 @@ void NoFilterProc_Affine(const SkBitmapProcState& s, uint32_t xy[],
                              SkMatrix::kScale_Mask |
                              SkMatrix::kAffine_Mask)) == 0);
 
-    SkPoint srcPt;
-    s.fInvProc(s.fInvMatrix,
-               SkIntToScalar(x) + SK_ScalarHalf,
-               SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
-
-    SkFractionalInt fx = SkScalarToFractionalInt(srcPt.fX);
-    SkFractionalInt fy = SkScalarToFractionalInt(srcPt.fY);
+    const SkBitmapProcStateAutoMapper mapper(s, x ,y);
+    SkFractionalInt fx = SkFixedToFractionalInt(mapper.x());
+    SkFractionalInt fy = SkFixedToFractionalInt(mapper.y());
     SkFractionalInt dx = s.fInvSxFractionalInt;
     SkFractionalInt dy = s.fInvKyFractionalInt;
     int maxX = s.fPixmap.width() - 1;
@@ -107,6 +100,7 @@ void NoFilterProc_Persp(const SkBitmapProcState& s, uint32_t* SK_RESTRICT xy,
     int maxX = s.fPixmap.width() - 1;
     int maxY = s.fPixmap.height() - 1;
 
+    // TODO: inv bias support
     SkPerspIter   iter(s.fInvMatrix,
                        SkIntToScalar(x) + SK_ScalarHalf,
                        SkIntToScalar(y) + SK_ScalarHalf, count);