Repeating 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);
-#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 31 matching lines @@
     FixedTileProc       fTileProcY;         // chooseProcs
     FixedTileLowBitsProc fTileLowBitsProcX; // chooseProcs
     FixedTileLowBitsProc fTileLowBitsProcY; // chooseProcs
     IntTileProc         fIntTileProcY;      // chooseProcs
     SkFixed             fFilterOneX;
     SkFixed             fFilterOneY;
 
     SkPMColor           fPaintPMColor;      // chooseProcs - A8 config
     SkFixed             fInvSx;             // chooseProcs
     SkFixed             fInvKy;             // chooseProcs
+
+    // Epsilon bias to ensure inverse-mapped bitmap coordinates are rounded consistently WRT
+    // geometry.  These are treated as SkFixed, but we only store the fractional part.

[reed1, 2015/12/16 16:25:03]

We just need 0 or 1 for each, right? why using int16_t?

[f(malita), 2015/12/16 16:45:55]

The current impl also expects an explicit sign.  We could

a) make the sign implicit and squeeze these down to 1 bit each
b) squeeze them down to int8_ts - I think these should fit in the struct padding
if placed at the end

Do you think b) will work?

+    int16_t             fInvBiasX;          // chooseProcs
+    int16_t             fInvBiasY;          // chooseProcs
+
     uint16_t            fAlphaScale;        // chooseProcs
     uint8_t             fInvType;           // chooseProcs
     uint8_t             fTileModeX;         // CONSTRUCTOR
     uint8_t             fTileModeY;         // CONSTRUCTOR
     uint8_t             fFilterLevel;       // chooseProcs
 
     /** Platforms implement this, and can optionally overwrite only the
         following fields:
 
         fShaderProc32
@@ skipping 106 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