SkBitmapProcState rounding bias

src/core/SkBitmapProcState.h

 /*
  * Copyright 2007 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkBitmapProcState_DEFINED
 #define SkBitmapProcState_DEFINED
 
 #include "SkBitmap.h"
 #include "SkBitmapController.h"
 #include "SkBitmapFilter.h"
 #include "SkBitmapProvider.h"
+#include "SkFloatBits.h"
 #include "SkMatrix.h"
 #include "SkMipMap.h"
 #include "SkPaint.h"
 #include "SkShader.h"
 #include "SkTemplates.h"
 
 typedef SkFixed3232    SkFractionalInt;
 #define SkScalarToFractionalInt(x)  SkScalarToFixed3232(x)
 #define SkFractionalIntToFixed(x)   SkFixed3232ToFixed(x)
 #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 {
     SkBitmapProcState(const SkBitmapProvider&, SkShader::TileMode tmx, SkShader::TileMode tmy);
     SkBitmapProcState(const SkBitmap&, SkShader::TileMode tmx, SkShader::TileMode tmy);
     ~SkBitmapProcState();
 
     typedef void (*ShaderProc32)(const SkBitmapProcState&, int x, int y,
                                  SkPMColor[], int count);
 
@@ skipping 157 matching lines @@
 void ClampX_ClampY_filter_affine(const SkBitmapProcState& s,
                                  uint32_t xy[], int count, int x, int y);
 void ClampX_ClampY_nofilter_affine(const SkBitmapProcState& s,
                                    uint32_t xy[], int count, int x, int y);
 void S32_D16_filter_DX(const SkBitmapProcState& s,
                        const uint32_t* xy, int count, uint16_t* colors);
 void S32_D16_filter_DXDY(const SkBitmapProcState& s,
                          const uint32_t* xy, int count, uint16_t* colors);
 
 #endif