SkBitmapProcState rounding bias

src/core/SkBitmapProcState.h

Index: src/core/SkBitmapProcState.h
diff --git a/src/core/SkBitmapProcState.h b/src/core/SkBitmapProcState.h
index 2ce76bc83ec7527f5797a8a55d5d5b53fd58cfa4..395da46c4fd7539e9017f123193839729793faf0 100644
--- a/src/core/SkBitmapProcState.h
+++ b/src/core/SkBitmapProcState.h
@@ -12,6 +12,7 @@
 #include "SkBitmapController.h"
 #include "SkBitmapFilter.h"
 #include "SkBitmapProvider.h"
+#include "SkFloatBits.h"
 #include "SkMatrix.h"
 #include "SkMipMap.h"
 #include "SkPaint.h"
@@ -24,6 +25,18 @@ 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 ? -1 : 0;

[reed1, 2015/12/14 21:50:07]

seems like this >= version might be faster (certainly easier to read)

return -(scale > 0);

[f(malita), 2015/12/15 14:34:13]

Done.

+    return (static_cast<uint32_t>(SkFloat2Bits(SkScalarToFloat(scale))) >> 31) - 1;
+#else
+    return 0;
+#endif
+}
+
 class SkPaint;
 
 struct SkBitmapProcState {