fix analytic AA to work with even rounding

Bug: skia:
Change-Id: I92b19baa06429ef2c0e9cf6928d63528f29943fe
Reviewed-on: https://skia-review.googlesource.com/42520
Reviewed-by: Yuqian Li <liyuqian@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/core/SkAnalyticEdge.h b/src/core/SkAnalyticEdge.h
index 13f62571a9..5e8403f5ec 100644
--- a/src/core/SkAnalyticEdge.h
+++ b/src/core/SkAnalyticEdge.h
@@ -139,11 +139,18 @@ bool SkAnalyticEdge::setLine(const SkPoint& p0, const SkPoint& p1) {
     // We must set X/Y using the same way (e.g., times 4, to FDot6, then to Fixed) as Quads/Cubics.
     // Otherwise the order of the edge might be wrong due to precision limit.
     const int accuracy = kDefaultAccuracy;
+#ifdef SK_RASTERIZE_EVEN_ROUNDING
+    SkFixed x0 = SkFDot6ToFixed(SkScalarRoundToFDot6(p0.fX, accuracy)) >> accuracy;
+    SkFixed y0 = SnapY(SkFDot6ToFixed(SkScalarRoundToFDot6(p0.fY, accuracy)) >> accuracy);
+    SkFixed x1 = SkFDot6ToFixed(SkScalarRoundToFDot6(p1.fX, accuracy)) >> accuracy;
+    SkFixed y1 = SnapY(SkFDot6ToFixed(SkScalarRoundToFDot6(p1.fY, accuracy)) >> accuracy);
+#else
     const int multiplier = (1 << kDefaultAccuracy);
     SkFixed x0 = SkFDot6ToFixed(SkScalarToFDot6(p0.fX * multiplier)) >> accuracy;
     SkFixed y0 = SnapY(SkFDot6ToFixed(SkScalarToFDot6(p0.fY * multiplier)) >> accuracy);
     SkFixed x1 = SkFDot6ToFixed(SkScalarToFDot6(p1.fX * multiplier)) >> accuracy;
     SkFixed y1 = SnapY(SkFDot6ToFixed(SkScalarToFDot6(p1.fY * multiplier)) >> accuracy);
+#endif
 
     int winding = 1;
 
@@ -186,8 +193,12 @@ struct SkBezier {
     // See if left shift, covert to SkFDot6, and round has the same top and bottom y.
     // If so, the edge will be empty.
     static inline bool IsEmpty(SkScalar y0, SkScalar y1, int shift = 2) {
+#ifdef SK_RASTERIZE_EVEN_ROUNDING
+        return SkScalarRoundToFDot6(y0, shift) == SkScalarRoundToFDot6(y1, shift);
+#else
         SkScalar scale = (1 << (shift + 6));
         return SkFDot6Round(int(y0 * scale)) == SkFDot6Round(int(y1 * scale));
+#endif
     }
 };