text: 
  /*
   * Copyright 2006 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.
   */
  
  #include "SkXfermode.h"
  #include "SkXfermode_opts_SSE2.h"
  #include "SkXfermode_proccoeff.h"
  #include "SkColorPriv.h"
  #include "SkLazyPtr.h"
  #include "SkMathPriv.h"
  #include "SkReadBuffer.h"
  #include "SkString.h"
  #include "SkUtilsArm.h"
  #include "SkWriteBuffer.h"
  
  #if !SK_ARM_NEON_IS_NONE
  #include "SkXfermode_opts_arm_neon.h"
  #endif
  
  #define SkAlphaMulAlpha(a, b)   SkMulDiv255Round(a, b)
  
  #if 0
  // idea for higher precision blends in xfer procs (and slightly faster)
  // see DstATop as a probable caller
  static U8CPU mulmuldiv255round(U8CPU a, U8CPU b, U8CPU c, U8CPU d) {
      SkASSERT(a <= 255);
      SkASSERT(b <= 255);
      SkASSERT(c <= 255);
      SkASSERT(d <= 255);
      unsigned prod = SkMulS16(a, b) + SkMulS16(c, d) + 128;
      unsigned result = (prod + (prod >> 8)) >> 8;
      SkASSERT(result <= 255);
      return result;
  }
  #endif
  
  static inline unsigned saturated_add(unsigned a, unsigned b) {
      SkASSERT(a <= 255);
      SkASSERT(b <= 255);
      unsigned sum = a + b;
      if (sum > 255) {
          sum = 255;
      }
      return sum;
  }
  
  static inline int clamp_signed_byte(int n) {
      if (n < 0) {
          n = 0;
      } else if (n > 255) {
          n = 255;
      }
      return n;
  }
  
  static inline int clamp_div255round(int prod) {
      if (prod <= 0) {
          return 0;
      } else if (prod >= 255*255) {
          return 255;
      } else {
          return SkDiv255Round(prod);
      }
  }
  
  ///////////////////////////////////////////////////////////////////////////////
  
  //  kClear_Mode,    //!< [0, 0]
  static SkPMColor clear_modeproc(SkPMColor src, SkPMColor dst) {
      return 0;
  }
  
  //  kSrc_Mode,      //!< [Sa, Sc]
  static SkPMColor src_modeproc(SkPMColor src, SkPMColor dst) {
      return src;
  }
  
  //  kDst_Mode,      //!< [Da, Dc]
  static SkPMColor dst_modeproc(SkPMColor src, SkPMColor dst) {
      return dst;
  }
  
  //  kSrcOver_Mode,  //!< [Sa + Da - Sa*Da, Sc + (1 - Sa)*Dc]
  static SkPMColor srcover_modeproc(SkPMColor src, SkPMColor dst) {
  #if 0
      // this is the old, more-correct way, but it doesn't guarantee that dst==255
      // will always stay opaque
      return src + SkAlphaMulQ(dst, SkAlpha255To256(255 - SkGetPackedA32(src)));
  #else
      // this is slightly faster, but more importantly guarantees that dst==255
      // will always stay opaque
      return src + SkAlphaMulQ(dst, 256 - SkGetPackedA32(src));
  #endif
  }
  
  //  kDstOver_Mode,  //!< [Sa + Da - Sa*Da, Dc + (1 - Da)*Sc]
  static SkPMColor dstover_modeproc(SkPMColor src, SkPMColor dst) {
      // this is the reverse of srcover, just flipping src and dst
      // see srcover's comment about the 256 for opaqueness guarantees
      return dst + SkAlphaMulQ(src, 256 - SkGetPackedA32(dst));
  }
  
  //  kSrcIn_Mode,    //!< [Sa * Da, Sc * Da]
  static SkPMColor srcin_modeproc(SkPMColor src, SkPMColor dst) {
      return SkAlphaMulQ(src, SkAlpha255To256(SkGetPackedA32(dst)));
  }
  
  //  kDstIn_Mode,    //!< [Sa * Da, Sa * Dc]
  static SkPMColor dstin_modeproc(SkPMColor src, SkPMColor dst) {
      return SkAlphaMulQ(dst, SkAlpha255To256(SkGetPackedA32(src)));
  }
  
  //  kSrcOut_Mode,   //!< [Sa * (1 - Da), Sc * (1 - Da)]
  static SkPMColor srcout_modeproc(SkPMColor src, SkPMColor dst) {
      return SkAlphaMulQ(src, SkAlpha255To256(255 - SkGetPackedA32(dst)));
  }
  
  //  kDstOut_Mode,   //!< [Da * (1 - Sa), Dc * (1 - Sa)]
  static SkPMColor dstout_modeproc(SkPMColor src, SkPMColor dst) {
      return SkAlphaMulQ(dst, SkAlpha255To256(255 - SkGetPackedA32(src)));
  }
  
  //  kSrcATop_Mode,  //!< [Da, Sc * Da + (1 - Sa) * Dc]
  static SkPMColor srcatop_modeproc(SkPMColor src, SkPMColor dst) {
      unsigned sa = SkGetPackedA32(src);
      unsigned da = SkGetPackedA32(dst);
      unsigned isa = 255 - sa;
  
      return SkPackARGB32(da,
                          SkAlphaMulAlpha(da, SkGetPackedR32(src)) +
                              SkAlphaMulAlpha(isa, SkGetPackedR32(dst)),
                          SkAlphaMulAlpha(da, SkGetPackedG32(src)) +
                              SkAlphaMulAlpha(isa, SkGetPackedG32(dst)),
                          SkAlphaMulAlpha(da, SkGetPackedB32(src)) +
                              SkAlphaMulAlpha(isa, SkGetPackedB32(dst)));
  }
  
  //  kDstATop_Mode,  //!< [Sa, Sa * Dc + Sc * (1 - Da)]
  static SkPMColor dstatop_modeproc(SkPMColor src, SkPMColor dst) {
      unsigned sa = SkGetPackedA32(src);
      unsigned da = SkGetPackedA32(dst);
      unsigned ida = 255 - da;
  
      return SkPackARGB32(sa,
                          SkAlphaMulAlpha(ida, SkGetPackedR32(src)) +
                              SkAlphaMulAlpha(sa, SkGetPackedR32(dst)),
                          SkAlphaMulAlpha(ida, SkGetPackedG32(src)) +
                              SkAlphaMulAlpha(sa, SkGetPackedG32(dst)),
                          SkAlphaMulAlpha(ida, SkGetPackedB32(src)) +
                              SkAlphaMulAlpha(sa, SkGetPackedB32(dst)));
  }
  
  //  kXor_Mode   [Sa + Da - 2 * Sa * Da, Sc * (1 - Da) + (1 - Sa) * Dc]
  static SkPMColor xor_modeproc(SkPMColor src, SkPMColor dst) {
      unsigned sa = SkGetPackedA32(src);
      unsigned da = SkGetPackedA32(dst);
      unsigned isa = 255 - sa;
      unsigned ida = 255 - da;
  
      return SkPackARGB32(sa + da - (SkAlphaMulAlpha(sa, da) << 1),
                          SkAlphaMulAlpha(ida, SkGetPackedR32(src)) +
                              SkAlphaMulAlpha(isa, SkGetPackedR32(dst)),
                          SkAlphaMulAlpha(ida, SkGetPackedG32(src)) +
                              SkAlphaMulAlpha(isa, SkGetPackedG32(dst)),
                          SkAlphaMulAlpha(ida, SkGetPackedB32(src)) +
                              SkAlphaMulAlpha(isa, SkGetPackedB32(dst)));
  }
  
  ///////////////////////////////////////////////////////////////////////////////
  
  // kPlus_Mode
  static SkPMColor plus_modeproc(SkPMColor src, SkPMColor dst) {
      unsigned b = saturated_add(SkGetPackedB32(src), SkGetPackedB32(dst));
      unsigned g = saturated_add(SkGetPackedG32(src), SkGetPackedG32(dst));
      unsigned r = saturated_add(SkGetPackedR32(src), SkGetPackedR32(dst));
      unsigned a = saturated_add(SkGetPackedA32(src), SkGetPackedA32(dst));
      return SkPackARGB32(a, r, g, b);
  }
  
  // kModulate_Mode
  static SkPMColor modulate_modeproc(SkPMColor src, SkPMColor dst) {
      int a = SkAlphaMulAlpha(SkGetPackedA32(src), SkGetPackedA32(dst));
      int r = SkAlphaMulAlpha(SkGetPackedR32(src), SkGetPackedR32(dst));
      int g = SkAlphaMulAlpha(SkGetPackedG32(src), SkGetPackedG32(dst));
      int b = SkAlphaMulAlpha(SkGetPackedB32(src), SkGetPackedB32(dst));
      return SkPackARGB32(a, r, g, b);
  }
  
  static inline int srcover_byte(int a, int b) {
      return a + b - SkAlphaMulAlpha(a, b);
  }
  
  // kMultiply_Mode
  // B(Cb, Cs) = Cb x Cs
  // multiply uses its own version of blendfunc_byte because sa and da are not needed
  static int blendfunc_multiply_byte(int sc, int dc, int sa, int da) {
      return clamp_div255round(sc * (255 - da)  + dc * (255 - sa)  + sc * dc);
  }
  
  static SkPMColor multiply_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = blendfunc_multiply_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = blendfunc_multiply_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = blendfunc_multiply_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kScreen_Mode
  static SkPMColor screen_modeproc(SkPMColor src, SkPMColor dst) {
      int a = srcover_byte(SkGetPackedA32(src), SkGetPackedA32(dst));
      int r = srcover_byte(SkGetPackedR32(src), SkGetPackedR32(dst));
      int g = srcover_byte(SkGetPackedG32(src), SkGetPackedG32(dst));
      int b = srcover_byte(SkGetPackedB32(src), SkGetPackedB32(dst));
      return SkPackARGB32(a, r, g, b);
  }
  
  // kOverlay_Mode
  static inline int overlay_byte(int sc, int dc, int sa, int da) {
      int tmp = sc * (255 - da) + dc * (255 - sa);
      int rc;
      if (2 * dc <= da) {
          rc = 2 * sc * dc;
      } else {
          rc = sa * da - 2 * (da - dc) * (sa - sc);
      }
      return clamp_div255round(rc + tmp);
  }
  static SkPMColor overlay_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = overlay_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = overlay_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = overlay_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kDarken_Mode
  static inline int darken_byte(int sc, int dc, int sa, int da) {
      int sd = sc * da;
      int ds = dc * sa;
      if (sd < ds) {
          // srcover
          return sc + dc - SkDiv255Round(ds);
      } else {
          // dstover
          return dc + sc - SkDiv255Round(sd);
      }
  }
  static SkPMColor darken_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = darken_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = darken_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = darken_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kLighten_Mode
  static inline int lighten_byte(int sc, int dc, int sa, int da) {
      int sd = sc * da;
      int ds = dc * sa;
      if (sd > ds) {
          // srcover
          return sc + dc - SkDiv255Round(ds);
      } else {
          // dstover
          return dc + sc - SkDiv255Round(sd);
      }
  }
  static SkPMColor lighten_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = lighten_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = lighten_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = lighten_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kColorDodge_Mode
  static inline int colordodge_byte(int sc, int dc, int sa, int da) {
      int diff = sa - sc;
      int rc;
      if (0 == dc) {
          return SkAlphaMulAlpha(sc, 255 - da);
      } else if (0 == diff) {
          rc = sa * da + sc * (255 - da) + dc * (255 - sa);
      } else {
          diff = dc * sa / diff;
          rc = sa * ((da < diff) ? da : diff) + sc * (255 - da) + dc * (255 - sa);
      }
      return clamp_div255round(rc);
  }
  static SkPMColor colordodge_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = colordodge_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = colordodge_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = colordodge_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kColorBurn_Mode
  static inline int colorburn_byte(int sc, int dc, int sa, int da) {
      int rc;
      if (dc == da) {
          rc = sa * da + sc * (255 - da) + dc * (255 - sa);
      } else if (0 == sc) {
          return SkAlphaMulAlpha(dc, 255 - sa);
      } else {
          int tmp = (da - dc) * sa / sc;
          rc = sa * (da - ((da < tmp) ? da : tmp))
              + sc * (255 - da) + dc * (255 - sa);
      }
      return clamp_div255round(rc);
  }
  static SkPMColor colorburn_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = colorburn_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = colorburn_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = colorburn_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kHardLight_Mode
  static inline int hardlight_byte(int sc, int dc, int sa, int da) {
      int rc;
      if (2 * sc <= sa) {
          rc = 2 * sc * dc;
      } else {
          rc = sa * da - 2 * (da - dc) * (sa - sc);
      }
      return clamp_div255round(rc + sc * (255 - da) + dc * (255 - sa));
  }
  static SkPMColor hardlight_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = hardlight_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = hardlight_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = hardlight_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // returns 255 * sqrt(n/255)
  static U8CPU sqrt_unit_byte(U8CPU n) {
      return SkSqrtBits(n, 15+4);
  }
  
  // kSoftLight_Mode
  static inline int softlight_byte(int sc, int dc, int sa, int da) {
      int m = da ? dc * 256 / da : 0;
      int rc;
      if (2 * sc <= sa) {
          rc = dc * (sa + ((2 * sc - sa) * (256 - m) >> 8));
      } else if (4 * dc <= da) {
          int tmp = (4 * m * (4 * m + 256) * (m - 256) >> 16) + 7 * m;
          rc = dc * sa + (da * (2 * sc - sa) * tmp >> 8);
      } else {
          int tmp = sqrt_unit_byte(m) - m;
          rc = dc * sa + (da * (2 * sc - sa) * tmp >> 8);
      }
      return clamp_div255round(rc + sc * (255 - da) + dc * (255 - sa));
  }
  static SkPMColor softlight_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = softlight_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = softlight_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = softlight_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kDifference_Mode
  static inline int difference_byte(int sc, int dc, int sa, int da) {
      int tmp = SkMin32(sc * da, dc * sa);
      return clamp_signed_byte(sc + dc - 2 * SkDiv255Round(tmp));
  }
  static SkPMColor difference_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = difference_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = difference_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = difference_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kExclusion_Mode
  static inline int exclusion_byte(int sc, int dc, int, int) {
      // this equations is wacky, wait for SVG to confirm it
      //int r = sc * da + dc * sa - 2 * sc * dc + sc * (255 - da) + dc * (255 - sa);
  
      // The above equation can be simplified as follows
      int r = 255*(sc + dc) - 2 * sc * dc;
      return clamp_div255round(r);
  }
  static SkPMColor exclusion_modeproc(SkPMColor src, SkPMColor dst) {
      int sa = SkGetPackedA32(src);
      int da = SkGetPackedA32(dst);
      int a = srcover_byte(sa, da);
      int r = exclusion_byte(SkGetPackedR32(src), SkGetPackedR32(dst), sa, da);
      int g = exclusion_byte(SkGetPackedG32(src), SkGetPackedG32(dst), sa, da);
      int b = exclusion_byte(SkGetPackedB32(src), SkGetPackedB32(dst), sa, da);
      return SkPackARGB32(a, r, g, b);
  }
  
  // The CSS compositing spec introduces the following formulas:
  // (See https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#blendingnonseparable)
  // SkComputeLuminance is similar to this formula but it uses the new definition from Rec. 709
  // while PDF and CG uses the one from Rec. Rec. 601
  // See http://www.glennchan.info/articles/technical/hd-versus-sd-color-space/hd-versus-sd-color-space.htm
  static inline int Lum(int r, int g, int b)
  {
      return SkDiv255Round(r * 77 + g * 150 + b * 28);
  }
  
  static inline int min2(int a, int b) { return a < b ? a : b; }
  static inline int max2(int a, int b) { return a > b ? a : b; }
  #define minimum(a, b, c) min2(min2(a, b), c)
  #define maximum(a, b, c) max2(max2(a, b), c)
  
  static inline int Sat(int r, int g, int b) {
      return maximum(r, g, b) - minimum(r, g, b);
  }
  
  static inline void setSaturationComponents(int* Cmin, int* Cmid, int* Cmax, int s) {
      if(*Cmax > *Cmin) {
          *Cmid =  SkMulDiv(*Cmid - *Cmin, s, *Cmax - *Cmin);
          *Cmax = s;
      } else {
          *Cmax = 0;
          *Cmid = 0;
      }
  
      *Cmin = 0;
  }
  
  static inline void SetSat(int* r, int* g, int* b, int s) {
      if(*r <= *g) {
          if(*g <= *b) {
              setSaturationComponents(r, g, b, s);
          } else if(*r <= *b) {
              setSaturationComponents(r, b, g, s);
          } else {
              setSaturationComponents(b, r, g, s);
          }
      } else if(*r <= *b) {
          setSaturationComponents(g, r, b, s);
      } else if(*g <= *b) {
          setSaturationComponents(g, b, r, s);
      } else {
          setSaturationComponents(b, g, r, s);
      }
  }
  
  static inline void clipColor(int* r, int* g, int* b, int a) {
      int L = Lum(*r, *g, *b);
      int n = minimum(*r, *g, *b);
      int x = maximum(*r, *g, *b);
      int denom;
      if ((n < 0) && (denom = L - n)) { // Compute denom and make sure it's non zero
         *r = L + SkMulDiv(*r - L, L, denom);
         *g = L + SkMulDiv(*g - L, L, denom);
         *b = L + SkMulDiv(*b - L, L, denom);
      }
  
      if ((x > a) && (denom = x - L)) { // Compute denom and make sure it's non zero
         int numer = a - L;
         *r = L + SkMulDiv(*r - L, numer, denom);
         *g = L + SkMulDiv(*g - L, numer, denom);
         *b = L + SkMulDiv(*b - L, numer, denom);
      }
  }
  
  static inline void SetLum(int* r, int* g, int* b, int a, int l) {
    int d = l - Lum(*r, *g, *b);
    *r +=  d;
    *g +=  d;
    *b +=  d;
  
    clipColor(r, g, b, a);
  }
  
  // non-separable blend modes are done in non-premultiplied alpha
  #define  blendfunc_nonsep_byte(sc, dc, sa, da, blendval) \
    clamp_div255round(sc * (255 - da) +  dc * (255 - sa) + blendval)
  
  // kHue_Mode
  // B(Cb, Cs) = SetLum(SetSat(Cs, Sat(Cb)), Lum(Cb))
  // Create a color with the hue of the source color and the saturation and luminosity of the backdrop color.
  static SkPMColor hue_modeproc(SkPMColor src, SkPMColor dst) {
      int sr = SkGetPackedR32(src);
      int sg = SkGetPackedG32(src);
      int sb = SkGetPackedB32(src);
      int sa = SkGetPackedA32(src);
  
      int dr = SkGetPackedR32(dst);
      int dg = SkGetPackedG32(dst);
      int db = SkGetPackedB32(dst);
      int da = SkGetPackedA32(dst);
      int Sr, Sg, Sb;
  
      if(sa && da) {
          Sr = sr * sa;
          Sg = sg * sa;
          Sb = sb * sa;
          SetSat(&Sr, &Sg, &Sb, Sat(dr, dg, db) * sa);
          SetLum(&Sr, &Sg, &Sb, sa * da, Lum(dr, dg, db) * sa);
      } else {
          Sr = 0;
          Sg = 0;
          Sb = 0;
      }
  
      int a = srcover_byte(sa, da);
      int r = blendfunc_nonsep_byte(sr, dr, sa, da, Sr);
      int g = blendfunc_nonsep_byte(sg, dg, sa, da, Sg);
      int b = blendfunc_nonsep_byte(sb, db, sa, da, Sb);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kSaturation_Mode
  // B(Cb, Cs) = SetLum(SetSat(Cb, Sat(Cs)), Lum(Cb))
  // Create a color with the saturation of the source color and the hue and luminosity of the backdrop color.
  static SkPMColor saturation_modeproc(SkPMColor src, SkPMColor dst) {
      int sr = SkGetPackedR32(src);
      int sg = SkGetPackedG32(src);
      int sb = SkGetPackedB32(src);
      int sa = SkGetPackedA32(src);
  
      int dr = SkGetPackedR32(dst);
      int dg = SkGetPackedG32(dst);
      int db = SkGetPackedB32(dst);
      int da = SkGetPackedA32(dst);
      int Dr, Dg, Db;
  
      if(sa && da) {
          Dr = dr * sa;
          Dg = dg * sa;
          Db = db * sa;
          SetSat(&Dr, &Dg, &Db, Sat(sr, sg, sb) * da);
          SetLum(&Dr, &Dg, &Db, sa * da, Lum(dr, dg, db) * sa);
      } else {
          Dr = 0;
          Dg = 0;
          Db = 0;
      }
  
      int a = srcover_byte(sa, da);
      int r = blendfunc_nonsep_byte(sr, dr, sa, da, Dr);
      int g = blendfunc_nonsep_byte(sg, dg, sa, da, Dg);
      int b = blendfunc_nonsep_byte(sb, db, sa, da, Db);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kColor_Mode
  // B(Cb, Cs) = SetLum(Cs, Lum(Cb))
  // Create a color with the hue and saturation of the source color and the luminosity of the backdrop color.
  static SkPMColor color_modeproc(SkPMColor src, SkPMColor dst) {
      int sr = SkGetPackedR32(src);
      int sg = SkGetPackedG32(src);
      int sb = SkGetPackedB32(src);
      int sa = SkGetPackedA32(src);
  
      int dr = SkGetPackedR32(dst);
      int dg = SkGetPackedG32(dst);
      int db = SkGetPackedB32(dst);
      int da = SkGetPackedA32(dst);
      int Sr, Sg, Sb;
  
      if(sa && da) {
          Sr = sr * da;
          Sg = sg * da;
          Sb = sb * da;
          SetLum(&Sr, &Sg, &Sb, sa * da, Lum(dr, dg, db) * sa);
      } else {
          Sr = 0;
          Sg = 0;
          Sb = 0;
      }
  
      int a = srcover_byte(sa, da);
      int r = blendfunc_nonsep_byte(sr, dr, sa, da, Sr);
      int g = blendfunc_nonsep_byte(sg, dg, sa, da, Sg);
      int b = blendfunc_nonsep_byte(sb, db, sa, da, Sb);
      return SkPackARGB32(a, r, g, b);
  }
  
  // kLuminosity_Mode
  // B(Cb, Cs) = SetLum(Cb, Lum(Cs))
  // Create a color with the luminosity of the source color and the hue and saturation of the backdrop color.
  static SkPMColor luminosity_modeproc(SkPMColor src, SkPMColor dst) {
      int sr = SkGetPackedR32(src);
      int sg = SkGetPackedG32(src);
      int sb = SkGetPackedB32(src);
      int sa = SkGetPackedA32(src);
  
      int dr = SkGetPackedR32(dst);
      int dg = SkGetPackedG32(dst);
      int db = SkGetPackedB32(dst);
      int da = SkGetPackedA32(dst);
      int Dr, Dg, Db;
  
      if(sa && da) {
          Dr = dr * sa;
          Dg = dg * sa;
          Db = db * sa;
          SetLum(&Dr, &Dg, &Db, sa * da, Lum(sr, sg, sb) * da);
      } else {
          Dr = 0;
          Dg = 0;
          Db = 0;
      }
  
      int a = srcover_byte(sa, da);
      int r = blendfunc_nonsep_byte(sr, dr, sa, da, Dr);
      int g = blendfunc_nonsep_byte(sg, dg, sa, da, Dg);
      int b = blendfunc_nonsep_byte(sb, db, sa, da, Db);
      return SkPackARGB32(a, r, g, b);
  }
  
  const ProcCoeff gProcCoeffs[] = {
      { clear_modeproc,   SkXfermode::kZero_Coeff,    SkXfermode::kZero_Coeff },
      { src_modeproc,     SkXfermode::kOne_Coeff,     SkXfermode::kZero_Coeff },
      { dst_modeproc,     SkXfermode::kZero_Coeff,    SkXfermode::kOne_Coeff },
      { srcover_modeproc, SkXfermode::kOne_Coeff,     SkXfermode::kISA_Coeff },
      { dstover_modeproc, SkXfermode::kIDA_Coeff,     SkXfermode::kOne_Coeff },
      { srcin_modeproc,   SkXfermode::kDA_Coeff,      SkXfermode::kZero_Coeff },
      { dstin_modeproc,   SkXfermode::kZero_Coeff,    SkXfermode::kSA_Coeff },
      { srcout_modeproc,  SkXfermode::kIDA_Coeff,     SkXfermode::kZero_Coeff },
      { dstout_modeproc,  SkXfermode::kZero_Coeff,    SkXfermode::kISA_Coeff },
      { srcatop_modeproc, SkXfermode::kDA_Coeff,      SkXfermode::kISA_Coeff },
      { dstatop_modeproc, SkXfermode::kIDA_Coeff,     SkXfermode::kSA_Coeff },
      { xor_modeproc,     SkXfermode::kIDA_Coeff,     SkXfermode::kISA_Coeff },
  
      { plus_modeproc,    SkXfermode::kOne_Coeff,     SkXfermode::kOne_Coeff },
      { modulate_modeproc,SkXfermode::kZero_Coeff,    SkXfermode::kSC_Coeff },
      { screen_modeproc,  SkXfermode::kOne_Coeff,     SkXfermode::kISC_Coeff },
      { overlay_modeproc,     CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { darken_modeproc,      CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { lighten_modeproc,     CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { colordodge_modeproc,  CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { colorburn_modeproc,   CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { hardlight_modeproc,   CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { softlight_modeproc,   CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { difference_modeproc,  CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { exclusion_modeproc,   CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { multiply_modeproc,    CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { hue_modeproc,         CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { saturation_modeproc,  CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { color_modeproc,       CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
      { luminosity_modeproc,  CANNOT_USE_COEFF,       CANNOT_USE_COEFF },
  };
  
  ///////////////////////////////////////////////////////////////////////////////
  
  bool SkXfermode::asCoeff(Coeff* src, Coeff* dst) const {
      return false;
  }
  
  bool SkXfermode::asMode(Mode* mode) const {
      return false;
  }
  
  bool SkXfermode::asFragmentProcessor(GrFragmentProcessor**, GrTexture*) const {
      return false;
  }
  
  bool SkXfermode::asXPFactory(GrXPFactory**) const {
      return false;
  }
  
  
  #if SK_SUPPORT_GPU
  #include "effects/GrPorterDuffXferProcessor.h"
  
  bool SkXfermode::AsFragmentProcessorOrXPFactory(SkXfermode* xfermode,
                                                  GrFragmentProcessor** fp,
                                                  GrXPFactory** xpf) {
      Coeff src, dst;
      Mode mode;
      if (NULL == xfermode) {
          *xpf = GrPorterDuffXPFactory::Create(kSrcOver_Mode);
          return true;
      } else if (xfermode->asMode(&mode) && mode <= kLastCoeffMode) {
          *xpf = GrPorterDuffXPFactory::Create(mode);
          return true;
      } else if (xfermode->asCoeff(&src, &dst)) {
          *xpf = GrPorterDuffXPFactory::Create(src, dst);
          return true;
      } else if (xfermode->asXPFactory(xpf)) {
          return true;
      } else {
          return xfermode->asFragmentProcessor(fp);
      }
  }
  #else
  bool SkXfermode::AsFragmentProcessorOrXPFactory(SkXfermode* xfermode,
                                                  GrFragmentProcessor** fp,
                                                  GrXPFactory** xpf) {
      return false;
  }
  #endif
  
  SkPMColor SkXfermode::xferColor(SkPMColor src, SkPMColor dst) const{
      // no-op. subclasses should override this
      return dst;
  }
  
  void SkXfermode::xfer32(SkPMColor* SK_RESTRICT dst,
                          const SkPMColor* SK_RESTRICT src, int count,
                          const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src && count >= 0);
  
      if (NULL == aa) {
          for (int i = count - 1; i >= 0; --i) {
              dst[i] = this->xferColor(src[i], dst[i]);
          }
      } else {
          for (int i = count - 1; i >= 0; --i) {
              unsigned a = aa[i];
              if (0 != a) {
                  SkPMColor dstC = dst[i];
                  SkPMColor C = this->xferColor(src[i], dstC);
                  if (0xFF != a) {
                      C = SkFourByteInterp(C, dstC, a);
                  }
                  dst[i] = C;
              }
          }
      }
  }
  
  void SkXfermode::xfer16(uint16_t* dst,
                          const SkPMColor* SK_RESTRICT src, int count,
                          const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src && count >= 0);
  
      if (NULL == aa) {
          for (int i = count - 1; i >= 0; --i) {
              SkPMColor dstC = SkPixel16ToPixel32(dst[i]);
              dst[i] = SkPixel32ToPixel16_ToU16(this->xferColor(src[i], dstC));
          }
      } else {
          for (int i = count - 1; i >= 0; --i) {
              unsigned a = aa[i];
              if (0 != a) {
                  SkPMColor dstC = SkPixel16ToPixel32(dst[i]);
                  SkPMColor C = this->xferColor(src[i], dstC);
                  if (0xFF != a) {
                      C = SkFourByteInterp(C, dstC, a);
                  }
                  dst[i] = SkPixel32ToPixel16_ToU16(C);
              }
          }
      }
  }
  
  void SkXfermode::xferA8(SkAlpha* SK_RESTRICT dst,
                          const SkPMColor src[], int count,
                          const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src && count >= 0);
  
      if (NULL == aa) {
          for (int i = count - 1; i >= 0; --i) {
              SkPMColor res = this->xferColor(src[i], (dst[i] << SK_A32_SHIFT));
              dst[i] = SkToU8(SkGetPackedA32(res));
          }
      } else {
          for (int i = count - 1; i >= 0; --i) {
              unsigned a = aa[i];
              if (0 != a) {
                  SkAlpha dstA = dst[i];
                  unsigned A = SkGetPackedA32(this->xferColor(src[i],
                                              (SkPMColor)(dstA << SK_A32_SHIFT)));
                  if (0xFF != a) {
                      A = SkAlphaBlend(A, dstA, SkAlpha255To256(a));
                  }
                  dst[i] = SkToU8(A);
              }
          }
      }
  }
  
  //////////////////////////////////////////////////////////////////////////////
  
  #if SK_SUPPORT_GPU
  
  #include "GrFragmentProcessor.h"
  #include "GrCoordTransform.h"
  #include "GrInvariantOutput.h"
  #include "GrProcessorUnitTest.h"
  #include "gl/GrGLProcessor.h"
  #include "gl/builders/GrGLProgramBuilder.h"
  
  /**
   * GrProcessor that implements the all the separable xfer modes that cannot be expressed as Coeffs.
   */
  class XferEffect : public GrFragmentProcessor {
  public:
      static bool IsSupportedMode(SkXfermode::Mode mode) {
          return mode > SkXfermode::kLastCoeffMode && mode <= SkXfermode::kLastMode;
      }
  
      static GrFragmentProcessor* Create(SkXfermode::Mode mode, GrTexture* background) {
          if (!IsSupportedMode(mode)) {
              return NULL;
          } else {
              return SkNEW_ARGS(XferEffect, (mode, background));
          }
      }
  
      virtual void getGLProcessorKey(const GrGLCaps& caps,
                                     GrProcessorKeyBuilder* b) const SK_OVERRIDE {
          GLProcessor::GenKey(*this, caps, b);
      }
  
      virtual GrGLFragmentProcessor* createGLInstance() const SK_OVERRIDE {
          return SkNEW_ARGS(GLProcessor, (*this));
      }
  
      virtual const char* name() const SK_OVERRIDE { return "XferEffect"; }
  
      SkXfermode::Mode mode() const { return fMode; }
      const GrTextureAccess&  backgroundAccess() const { return fBackgroundAccess; }
  
      class GLProcessor : public GrGLFragmentProcessor {
      public:
          GLProcessor(const GrFragmentProcessor&) {}
  
          virtual void emitCode(GrGLFPBuilder* builder,
                                const GrFragmentProcessor& fp,
                                const char* outputColor,
                                const char* inputColor,
                                const TransformedCoordsArray& coords,
                                const TextureSamplerArray& samplers) SK_OVERRIDE {
              SkXfermode::Mode mode = fp.cast<XferEffect>().mode();
              const GrTexture* backgroundTex =
                      fp.cast<XferEffect>().backgroundAccess().getTexture();
              GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();
              const char* dstColor;
              if (backgroundTex) {
                  dstColor = "bgColor";
                  fsBuilder->codeAppendf("\t\tvec4 %s = ", dstColor);
                  fsBuilder->appendTextureLookup(samplers[0], coords[0].c_str(), coords[0].getType());
                  fsBuilder->codeAppendf(";\n");
              } else {
                  dstColor = fsBuilder->dstColor();
              }
              SkASSERT(dstColor);
  
              // We don't try to optimize for this case at all
              if (NULL == inputColor) {
                  fsBuilder->codeAppendf("\t\tconst vec4 ones = vec4(1);\n");
                  inputColor = "ones";
              }
              fsBuilder->codeAppendf("\t\t// SkXfermode::Mode: %s\n", SkXfermode::ModeName(mode));
  
              // These all perform src-over on the alpha channel.
              fsBuilder->codeAppendf("\t\t%s.a = %s.a + (1.0 - %s.a) * %s.a;\n",
                                      outputColor, inputColor, inputColor, dstColor);
  
              switch (mode) {
                  case SkXfermode::kOverlay_Mode:
                      // Overlay is Hard-Light with the src and dst reversed
                      HardLight(fsBuilder, outputColor, dstColor, inputColor);
                      break;
                  case SkXfermode::kDarken_Mode:
                      fsBuilder->codeAppendf("\t\t%s.rgb = min((1.0 - %s.a) * %s.rgb + %s.rgb, "
                                                              "(1.0 - %s.a) * %s.rgb + %s.rgb);\n",
                                              outputColor,
                                              inputColor, dstColor, inputColor,
                                              dstColor, inputColor, dstColor);
                      break;
                  case SkXfermode::kLighten_Mode:
                      fsBuilder->codeAppendf("\t\t%s.rgb = max((1.0 - %s.a) * %s.rgb + %s.rgb, "
                                                              "(1.0 - %s.a) * %s.rgb + %s.rgb);\n",
                                              outputColor,
                                              inputColor, dstColor, inputColor,
                                              dstColor, inputColor, dstColor);
                      break;
                  case SkXfermode::kColorDodge_Mode:
                      ColorDodgeComponent(fsBuilder, outputColor, inputColor, dstColor, 'r');
                      ColorDodgeComponent(fsBuilder, outputColor, inputColor, dstColor, 'g');
                      ColorDodgeComponent(fsBuilder, outputColor, inputColor, dstColor, 'b');
                      break;
                  case SkXfermode::kColorBurn_Mode:
                      ColorBurnComponent(fsBuilder, outputColor, inputColor, dstColor, 'r');
                      ColorBurnComponent(fsBuilder, outputColor, inputColor, dstColor, 'g');
                      ColorBurnComponent(fsBuilder, outputColor, inputColor, dstColor, 'b');
                      break;
                  case SkXfermode::kHardLight_Mode:
                      HardLight(fsBuilder, outputColor, inputColor, dstColor);
                      break;
                  case SkXfermode::kSoftLight_Mode:
                      fsBuilder->codeAppendf("\t\tif (0.0 == %s.a) {\n", dstColor);
                      fsBuilder->codeAppendf("\t\t\t%s.rgba = %s;\n", outputColor, inputColor);
                      fsBuilder->codeAppendf("\t\t} else {\n");
                      SoftLightComponentPosDstAlpha(fsBuilder, outputColor, inputColor, dstColor, 'r');
                      SoftLightComponentPosDstAlpha(fsBuilder, outputColor, inputColor, dstColor, 'g');
                      SoftLightComponentPosDstAlpha(fsBuilder, outputColor, inputColor, dstColor, 'b');
                      fsBuilder->codeAppendf("\t\t}\n");
                      break;
                  case SkXfermode::kDifference_Mode:
                      fsBuilder->codeAppendf("\t\t%s.rgb = %s.rgb + %s.rgb -"
                                                         "2.0 * min(%s.rgb * %s.a, %s.rgb * %s.a);\n",
                                             outputColor, inputColor, dstColor, inputColor, dstColor,
                                             dstColor, inputColor);
                      break;
                  case SkXfermode::kExclusion_Mode:
                      fsBuilder->codeAppendf("\t\t%s.rgb = %s.rgb + %s.rgb - "
                                                          "2.0 * %s.rgb * %s.rgb;\n",
                                             outputColor, dstColor, inputColor, dstColor, inputColor);
                      break;
                  case SkXfermode::kMultiply_Mode:
                      fsBuilder->codeAppendf("\t\t%s.rgb = (1.0 - %s.a) * %s.rgb + "
                                                          "(1.0 - %s.a) * %s.rgb + "
                                                           "%s.rgb * %s.rgb;\n",
                                             outputColor, inputColor, dstColor, dstColor, inputColor,
                                             inputColor, dstColor);
                      break;
                  case SkXfermode::kHue_Mode: {
                      //  SetLum(SetSat(S * Da, Sat(D * Sa)), Sa*Da, D*Sa) + (1 - Sa) * D + (1 - Da) * S
                      SkString setSat, setLum;
                      AddSatFunction(fsBuilder, &setSat);
                      AddLumFunction(fsBuilder, &setLum);
                      fsBuilder->codeAppendf("\t\tvec4 dstSrcAlpha = %s * %s.a;\n",
                                             dstColor, inputColor);
                      fsBuilder->codeAppendf("\t\t%s.rgb = %s(%s(%s.rgb * %s.a, dstSrcAlpha.rgb), dstSrcAlpha.a, dstSrcAlpha.rgb);\n",
                                             outputColor, setLum.c_str(), setSat.c_str(), inputColor,
                                             dstColor);
                      fsBuilder->codeAppendf("\t\t%s.rgb += (1.0 - %s.a) * %s.rgb + (1.0 - %s.a) * %s.rgb;\n",
                                             outputColor, inputColor, dstColor, dstColor, inputColor);
                      break;
                  }
                  case SkXfermode::kSaturation_Mode: {
                      // SetLum(SetSat(D * Sa, Sat(S * Da)), Sa*Da, D*Sa)) + (1 - Sa) * D + (1 - Da) * S
                      SkString setSat, setLum;
                      AddSatFunction(fsBuilder, &setSat);
                      AddLumFunction(fsBuilder, &setLum);
                      fsBuilder->codeAppendf("\t\tvec4 dstSrcAlpha = %s * %s.a;\n",
                                             dstColor, inputColor);
                      fsBuilder->codeAppendf("\t\t%s.rgb = %s(%s(dstSrcAlpha.rgb, %s.rgb * %s.a), dstSrcAlpha.a, dstSrcAlpha.rgb);\n",
                                             outputColor, setLum.c_str(), setSat.c_str(), inputColor,
                                             dstColor);
                      fsBuilder->codeAppendf("\t\t%s.rgb += (1.0 - %s.a) * %s.rgb + (1.0 - %s.a) * %s.rgb;\n",
                                             outputColor, inputColor, dstColor, dstColor, inputColor);
                      break;
                  }
                  case SkXfermode::kColor_Mode: {
                      //  SetLum(S * Da, Sa* Da, D * Sa) + (1 - Sa) * D + (1 - Da) * S
                      SkString setLum;
                      AddLumFunction(fsBuilder, &setLum);
                      fsBuilder->codeAppendf("\t\tvec4 srcDstAlpha = %s * %s.a;\n",
                                             inputColor, dstColor);
                      fsBuilder->codeAppendf("\t\t%s.rgb = %s(srcDstAlpha.rgb, srcDstAlpha.a, %s.rgb * %s.a);\n",
                                             outputColor, setLum.c_str(), dstColor, inputColor);
                      fsBuilder->codeAppendf("\t\t%s.rgb += (1.0 - %s.a) * %s.rgb + (1.0 - %s.a) * %s.rgb;\n",
                                             outputColor, inputColor, dstColor, dstColor, inputColor);
                      break;
                  }
                  case SkXfermode::kLuminosity_Mode: {
                      //  SetLum(D * Sa, Sa* Da, S * Da) + (1 - Sa) * D + (1 - Da) * S
                      SkString setLum;
                      AddLumFunction(fsBuilder, &setLum);
                      fsBuilder->codeAppendf("\t\tvec4 srcDstAlpha = %s * %s.a;\n",
                                             inputColor, dstColor);
                      fsBuilder->codeAppendf("\t\t%s.rgb = %s(%s.rgb * %s.a, srcDstAlpha.a, srcDstAlpha.rgb);\n",
                                             outputColor, setLum.c_str(), dstColor, inputColor);
                      fsBuilder->codeAppendf("\t\t%s.rgb += (1.0 - %s.a) * %s.rgb + (1.0 - %s.a) * %s.rgb;\n",
                                             outputColor, inputColor, dstColor, dstColor, inputColor);
                      break;
                  }
                  default:
                      SkFAIL("Unknown XferEffect mode.");
                      break;
              }
          }
  
          static inline void GenKey(const GrProcessor& proc, const GrGLCaps&,
                                    GrProcessorKeyBuilder* b) {
              // The background may come from the dst or from a texture.
              uint32_t key = proc.numTextures();
              SkASSERT(key <= 1);
              key |= proc.cast<XferEffect>().mode() << 1;
              b->add32(key);
          }
  
      private:
          static void HardLight(GrGLFPFragmentBuilder* fsBuilder,
                                const char* final,
                                const char* src,
                                const char* dst) {
              static const char kComponents[] = {'r', 'g', 'b'};
              for (size_t i = 0; i < SK_ARRAY_COUNT(kComponents); ++i) {
                  char component = kComponents[i];
                  fsBuilder->codeAppendf("\t\tif (2.0 * %s.%c <= %s.a) {\n", src, component, src);
                  fsBuilder->codeAppendf("\t\t\t%s.%c = 2.0 * %s.%c * %s.%c;\n", final, component, src, component, dst, component);
                  fsBuilder->codeAppend("\t\t} else {\n");
                  fsBuilder->codeAppendf("\t\t\t%s.%c = %s.a * %s.a - 2.0 * (%s.a - %s.%c) * (%s.a - %s.%c);\n",
                                         final, component, src, dst, dst, dst, component, src, src, component);
                  fsBuilder->codeAppend("\t\t}\n");
              }
              fsBuilder->codeAppendf("\t\t%s.rgb += %s.rgb * (1.0 - %s.a) + %s.rgb * (1.0 - %s.a);\n",
                                     final, src, dst, dst, src);
          }
  
          // Does one component of color-dodge
          static void ColorDodgeComponent(GrGLFPFragmentBuilder* fsBuilder,
                                          const char* final,
                                          const char* src,
                                          const char* dst,
                                          const char component) {
              fsBuilder->codeAppendf("\t\tif (0.0 == %s.%c) {\n", dst, component);
              fsBuilder->codeAppendf("\t\t\t%s.%c = %s.%c * (1.0 - %s.a);\n",
                                     final, component, src, component, dst);
              fsBuilder->codeAppend("\t\t} else {\n");
              fsBuilder->codeAppendf("\t\t\tfloat d = %s.a - %s.%c;\n", src, src, component);
              fsBuilder->codeAppend("\t\t\tif (0.0 == d) {\n");
              fsBuilder->codeAppendf("\t\t\t\t%s.%c = %s.a * %s.a + %s.%c * (1.0 - %s.a) + %s.%c * (1.0 - %s.a);\n",
                                     final, component, src, dst, src, component, dst, dst, component,
                                     src);
              fsBuilder->codeAppend("\t\t\t} else {\n");
              fsBuilder->codeAppendf("\t\t\t\td = min(%s.a, %s.%c * %s.a / d);\n",
                                     dst, dst, component, src);
              fsBuilder->codeAppendf("\t\t\t\t%s.%c = d * %s.a + %s.%c * (1.0 - %s.a) + %s.%c * (1.0 - %s.a);\n",
                                     final, component, src, src, component, dst, dst, component, src);
              fsBuilder->codeAppend("\t\t\t}\n");
              fsBuilder->codeAppend("\t\t}\n");
          }
  
          // Does one component of color-burn
          static void ColorBurnComponent(GrGLFPFragmentBuilder* fsBuilder,
                                         const char* final,
                                         const char* src,
                                         const char* dst,
                                         const char component) {
              fsBuilder->codeAppendf("\t\tif (%s.a == %s.%c) {\n", dst, dst, component);
              fsBuilder->codeAppendf("\t\t\t%s.%c = %s.a * %s.a + %s.%c * (1.0 - %s.a) + %s.%c * (1.0 - %s.a);\n",
                                     final, component, src, dst, src, component, dst, dst, component,
                                     src);
              fsBuilder->codeAppendf("\t\t} else if (0.0 == %s.%c) {\n", src, component);
              fsBuilder->codeAppendf("\t\t\t%s.%c = %s.%c * (1.0 - %s.a);\n",
                                     final, component, dst, component, src);
              fsBuilder->codeAppend("\t\t} else {\n");
              fsBuilder->codeAppendf("\t\t\tfloat d = max(0.0, %s.a - (%s.a - %s.%c) * %s.a / %s.%c);\n",
                                     dst, dst, dst, component, src, src, component);
              fsBuilder->codeAppendf("\t\t\t%s.%c = %s.a * d + %s.%c * (1.0 - %s.a) + %s.%c * (1.0 - %s.a);\n",
                                     final, component, src, src, component, dst, dst, component, src);
              fsBuilder->codeAppend("\t\t}\n");
          }
  
          // Does one component of soft-light. Caller should have already checked that dst alpha > 0.
          static void SoftLightComponentPosDstAlpha(GrGLFPFragmentBuilder* fsBuilder,
                                                    const char* final,
                                                    const char* src,
                                                    const char* dst,
                                                    const char component) {
              // if (2S < Sa)
              fsBuilder->codeAppendf("\t\t\tif (2.0 * %s.%c <= %s.a) {\n", src, component, src);
              // (D^2 (Sa-2 S))/Da+(1-Da) S+D (-Sa+2 S+1)
              fsBuilder->codeAppendf("\t\t\t\t%s.%c = (%s.%c*%s.%c*(%s.a - 2.0*%s.%c)) / %s.a + (1.0 - %s.a) * %s.%c + %s.%c*(-%s.a + 2.0*%s.%c + 1.0);\n",
                                     final, component, dst, component, dst, component, src, src,
                                     component, dst, dst, src, component, dst, component, src, src,
                                     component);
              // else if (4D < Da)
              fsBuilder->codeAppendf("\t\t\t} else if (4.0 * %s.%c <= %s.a) {\n",
                                     dst, component, dst);
              fsBuilder->codeAppendf("\t\t\t\tfloat DSqd = %s.%c * %s.%c;\n",
                                     dst, component, dst, component);
              fsBuilder->codeAppendf("\t\t\t\tfloat DCub = DSqd * %s.%c;\n", dst, component);
              fsBuilder->codeAppendf("\t\t\t\tfloat DaSqd = %s.a * %s.a;\n", dst, dst);
              fsBuilder->codeAppendf("\t\t\t\tfloat DaCub = DaSqd * %s.a;\n", dst);
              // (Da^3 (-S)+Da^2 (S-D (3 Sa-6 S-1))+12 Da D^2 (Sa-2 S)-16 D^3 (Sa-2 S))/Da^2
              fsBuilder->codeAppendf("\t\t\t\t%s.%c = (-DaCub*%s.%c + DaSqd*(%s.%c - %s.%c * (3.0*%s.a - 6.0*%s.%c - 1.0)) + 12.0*%s.a*DSqd*(%s.a - 2.0*%s.%c) - 16.0*DCub * (%s.a - 2.0*%s.%c)) / DaSqd;\n",
                                     final, component, src, component, src, component, dst, component,
                                     src, src, component, dst, src, src, component, src, src,
                                     component);
              fsBuilder->codeAppendf("\t\t\t} else {\n");
              // -sqrt(Da * D) (Sa-2 S)-Da S+D (Sa-2 S+1)+S
              fsBuilder->codeAppendf("\t\t\t\t%s.%c = -sqrt(%s.a*%s.%c)*(%s.a - 2.0*%s.%c) - %s.a*%s.%c + %s.%c*(%s.a - 2.0*%s.%c + 1.0) + %s.%c;\n",
                                      final, component, dst, dst, component, src, src, component, dst,
                                      src, component, dst, component, src, src, component, src,
                                      component);
              fsBuilder->codeAppendf("\t\t\t}\n");
          }
  
          // Adds a function that takes two colors and an alpha as input. It produces a color with the
          // hue and saturation of the first color, the luminosity of the second color, and the input
          // alpha. It has this signature:
          //      vec3 set_luminance(vec3 hueSatColor, float alpha, vec3 lumColor).
          static void AddLumFunction(GrGLFPFragmentBuilder* fsBuilder, SkString* setLumFunction) {
              // Emit a helper that gets the luminance of a color.
              SkString getFunction;
              GrGLShaderVar getLumArgs[] = {
                  GrGLShaderVar("color", kVec3f_GrSLType),
              };
              SkString getLumBody("\treturn dot(vec3(0.3, 0.59, 0.11), color);\n");
              fsBuilder->emitFunction(kFloat_GrSLType,
                                      "luminance",
                                      SK_ARRAY_COUNT(getLumArgs), getLumArgs,
                                      getLumBody.c_str(),
                                      &getFunction);
  
              // Emit the set luminance function.
              GrGLShaderVar setLumArgs[] = {
                  GrGLShaderVar("hueSat", kVec3f_GrSLType),
                  GrGLShaderVar("alpha", kFloat_GrSLType),
                  GrGLShaderVar("lumColor", kVec3f_GrSLType),
              };
              SkString setLumBody;
              setLumBody.printf("\tfloat diff = %s(lumColor - hueSat);\n", getFunction.c_str());
              setLumBody.append("\tvec3 outColor = hueSat + diff;\n");
              setLumBody.appendf("\tfloat outLum = %s(outColor);\n", getFunction.c_str());
              setLumBody.append("\tfloat minComp = min(min(outColor.r, outColor.g), outColor.b);\n"
                                "\tfloat maxComp = max(max(outColor.r, outColor.g), outColor.b);\n"
                                "\tif (minComp < 0.0 && outLum != minComp) {\n"
                                "\t\toutColor = outLum + ((outColor - vec3(outLum, outLum, outLum)) * outLum) / (outLum - minComp);\n"
                                "\t}\n"
                                "\tif (maxComp > alpha && maxComp != outLum) {\n"
                                "\t\toutColor = outLum + ((outColor - vec3(outLum, outLum, outLum)) * (alpha - outLum)) / (maxComp - outLum);\n"
                                "\t}\n"
                                "\treturn outColor;\n");
              fsBuilder->emitFunction(kVec3f_GrSLType,
                                      "set_luminance",
                                      SK_ARRAY_COUNT(setLumArgs), setLumArgs,
                                      setLumBody.c_str(),
                                      setLumFunction);
          }
  
          // Adds a function that creates a color with the hue and luminosity of one input color and
          // the saturation of another color. It will have this signature:
          //      float set_saturation(vec3 hueLumColor, vec3 satColor)
          static void AddSatFunction(GrGLFPFragmentBuilder* fsBuilder, SkString* setSatFunction) {
              // Emit a helper that gets the saturation of a color
              SkString getFunction;
              GrGLShaderVar getSatArgs[] = { GrGLShaderVar("color", kVec3f_GrSLType) };
              SkString getSatBody;
              getSatBody.printf("\treturn max(max(color.r, color.g), color.b) - "
                                "min(min(color.r, color.g), color.b);\n");
              fsBuilder->emitFunction(kFloat_GrSLType,
                                      "saturation",
                                      SK_ARRAY_COUNT(getSatArgs), getSatArgs,
                                      getSatBody.c_str(),
                                      &getFunction);
  
              // Emit a helper that sets the saturation given sorted input channels. This used
              // to use inout params for min, mid, and max components but that seems to cause
              // problems on PowerVR drivers. So instead it returns a vec3 where r, g ,b are the
              // adjusted min, mid, and max inputs, respectively.
              SkString helperFunction;
              GrGLShaderVar helperArgs[] = {
                  GrGLShaderVar("minComp", kFloat_GrSLType),
                  GrGLShaderVar("midComp", kFloat_GrSLType),
                  GrGLShaderVar("maxComp", kFloat_GrSLType),
                  GrGLShaderVar("sat", kFloat_GrSLType),
              };
              static const char kHelperBody[] = "\tif (minComp < maxComp) {\n"
                                                "\t\tvec3 result;\n"
                                                "\t\tresult.r = 0.0;\n"
                                                "\t\tresult.g = sat * (midComp - minComp) / (maxComp - minComp);\n"
                                                "\t\tresult.b = sat;\n"
                                                "\t\treturn result;\n"
                                                "\t} else {\n"
                                                "\t\treturn vec3(0, 0, 0);\n"
                                                "\t}\n";
              fsBuilder->emitFunction(kVec3f_GrSLType,
                                      "set_saturation_helper",
                                      SK_ARRAY_COUNT(helperArgs), helperArgs,
                                      kHelperBody,
                                      &helperFunction);
  
              GrGLShaderVar setSatArgs[] = {
                  GrGLShaderVar("hueLumColor", kVec3f_GrSLType),
                  GrGLShaderVar("satColor", kVec3f_GrSLType),
              };
              const char* helpFunc = helperFunction.c_str();
              SkString setSatBody;
              setSatBody.appendf("\tfloat sat = %s(satColor);\n"
                                 "\tif (hueLumColor.r <= hueLumColor.g) {\n"
                                 "\t\tif (hueLumColor.g <= hueLumColor.b) {\n"
                                 "\t\t\thueLumColor.rgb = %s(hueLumColor.r, hueLumColor.g, hueLumColor.b, sat);\n"
                                 "\t\t} else if (hueLumColor.r <= hueLumColor.b) {\n"
                                 "\t\t\thueLumColor.rbg = %s(hueLumColor.r, hueLumColor.b, hueLumColor.g, sat);\n"
                                 "\t\t} else {\n"
                                 "\t\t\thueLumColor.brg = %s(hueLumColor.b, hueLumColor.r, hueLumColor.g, sat);\n"
                                 "\t\t}\n"
                                 "\t} else if (hueLumColor.r <= hueLumColor.b) {\n"
                                 "\t\thueLumColor.grb = %s(hueLumColor.g, hueLumColor.r, hueLumColor.b, sat);\n"
                                 "\t} else if (hueLumColor.g <= hueLumColor.b) {\n"
                                 "\t\thueLumColor.gbr = %s(hueLumColor.g, hueLumColor.b, hueLumColor.r, sat);\n"
                                 "\t} else {\n"
                                 "\t\thueLumColor.bgr = %s(hueLumColor.b, hueLumColor.g, hueLumColor.r, sat);\n"
                                 "\t}\n"
                                 "\treturn hueLumColor;\n",
                                 getFunction.c_str(), helpFunc, helpFunc, helpFunc, helpFunc,
                                 helpFunc, helpFunc);
              fsBuilder->emitFunction(kVec3f_GrSLType,
                                      "set_saturation",
                                      SK_ARRAY_COUNT(setSatArgs), setSatArgs,
                                      setSatBody.c_str(),
                                      setSatFunction);
  
          }
  
          typedef GrGLFragmentProcessor INHERITED;
      };
  
      GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
  
  private:
      XferEffect(SkXfermode::Mode mode, GrTexture* background)
          : fMode(mode) {
          this->initClassID<XferEffect>();
          if (background) {
              fBackgroundTransform.reset(kLocal_GrCoordSet, background, 
                                         GrTextureParams::kNone_FilterMode);
              this->addCoordTransform(&fBackgroundTransform);
              fBackgroundAccess.reset(background);
              this->addTextureAccess(&fBackgroundAccess);
          } else {
              this->setWillReadDstColor();
          }
      }
      virtual bool onIsEqual(const GrFragmentProcessor& other) const SK_OVERRIDE {
          const XferEffect& s = other.cast<XferEffect>();
          return fMode == s.fMode;
      }
  
      virtual void onComputeInvariantOutput(GrInvariantOutput* inout) const SK_OVERRIDE {
          inout->setToUnknown(GrInvariantOutput::kWill_ReadInput);
      }
  
      SkXfermode::Mode fMode;
      GrCoordTransform fBackgroundTransform;
      GrTextureAccess  fBackgroundAccess;
  
      typedef GrFragmentProcessor INHERITED;
  };
  
  GR_DEFINE_FRAGMENT_PROCESSOR_TEST(XferEffect);
  GrFragmentProcessor* XferEffect::TestCreate(SkRandom* rand,
                                              GrContext*,
                                              const GrDrawTargetCaps&,
                                              GrTexture*[]) {
      int mode = rand->nextRangeU(SkXfermode::kLastCoeffMode + 1, SkXfermode::kLastSeparableMode);
  
      return SkNEW_ARGS(XferEffect, (static_cast<SkXfermode::Mode>(mode), NULL));
  }
  
  #endif
  
  ///////////////////////////////////////////////////////////////////////////////
  ///////////////////////////////////////////////////////////////////////////////
  
  SkFlattenable* SkProcCoeffXfermode::CreateProc(SkReadBuffer& buffer) {
      uint32_t mode32 = buffer.read32();
      if (!buffer.validate(mode32 < SK_ARRAY_COUNT(gProcCoeffs))) {
          return NULL;
      }
      return SkXfermode::Create((SkXfermode::Mode)mode32);
  }
  
  void SkProcCoeffXfermode::flatten(SkWriteBuffer& buffer) const {
      buffer.write32(fMode);
  }
  
  bool SkProcCoeffXfermode::asMode(Mode* mode) const {
      if (mode) {
          *mode = fMode;
      }
      return true;
  }
  
  bool SkProcCoeffXfermode::asCoeff(Coeff* sc, Coeff* dc) const {
      if (CANNOT_USE_COEFF == fSrcCoeff) {
          return false;
      }
  
      if (sc) {
          *sc = fSrcCoeff;
      }
      if (dc) {
          *dc = fDstCoeff;
      }
      return true;
  }
  
  void SkProcCoeffXfermode::xfer32(SkPMColor* SK_RESTRICT dst,
                                   const SkPMColor* SK_RESTRICT src, int count,
                                   const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src && count >= 0);
  
      SkXfermodeProc proc = fProc;
  
      if (proc) {
          if (NULL == aa) {
              for (int i = count - 1; i >= 0; --i) {
                  dst[i] = proc(src[i], dst[i]);
              }
          } else {
              for (int i = count - 1; i >= 0; --i) {
                  unsigned a = aa[i];
                  if (0 != a) {
                      SkPMColor dstC = dst[i];
                      SkPMColor C = proc(src[i], dstC);
                      if (a != 0xFF) {
                          C = SkFourByteInterp(C, dstC, a);
                      }
                      dst[i] = C;
                  }
              }
          }
      }
  }
  
  void SkProcCoeffXfermode::xfer16(uint16_t* SK_RESTRICT dst,
                                   const SkPMColor* SK_RESTRICT src, int count,
                                   const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src && count >= 0);
  
      SkXfermodeProc proc = fProc;
  
      if (proc) {
          if (NULL == aa) {
              for (int i = count - 1; i >= 0; --i) {
                  SkPMColor dstC = SkPixel16ToPixel32(dst[i]);
                  dst[i] = SkPixel32ToPixel16_ToU16(proc(src[i], dstC));
              }
          } else {
              for (int i = count - 1; i >= 0; --i) {
                  unsigned a = aa[i];
                  if (0 != a) {
                      SkPMColor dstC = SkPixel16ToPixel32(dst[i]);
                      SkPMColor C = proc(src[i], dstC);
                      if (0xFF != a) {
                          C = SkFourByteInterp(C, dstC, a);
                      }
                      dst[i] = SkPixel32ToPixel16_ToU16(C);
                  }
              }
          }
      }
  }
  
  void SkProcCoeffXfermode::xferA8(SkAlpha* SK_RESTRICT dst,
                                   const SkPMColor* SK_RESTRICT src, int count,
                                   const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src && count >= 0);
  
      SkXfermodeProc proc = fProc;
  
      if (proc) {
          if (NULL == aa) {
              for (int i = count - 1; i >= 0; --i) {
                  SkPMColor res = proc(src[i], dst[i] << SK_A32_SHIFT);
                  dst[i] = SkToU8(SkGetPackedA32(res));
              }
          } else {
              for (int i = count - 1; i >= 0; --i) {
                  unsigned a = aa[i];
                  if (0 != a) {
                      SkAlpha dstA = dst[i];
                      SkPMColor res = proc(src[i], dstA << SK_A32_SHIFT);
                      unsigned A = SkGetPackedA32(res);
                      if (0xFF != a) {
                          A = SkAlphaBlend(A, dstA, SkAlpha255To256(a));
                      }
                      dst[i] = SkToU8(A);
                  }
              }
          }
      }
  }
  
  #if SK_SUPPORT_GPU
  bool SkProcCoeffXfermode::asFragmentProcessor(GrFragmentProcessor** fp,
                                                GrTexture* background) const {
      if (XferEffect::IsSupportedMode(fMode)) {
          if (fp) {
              *fp = XferEffect::Create(fMode, background);
              SkASSERT(*fp);
          }
          return true;
      }
      return false;
  }
  #endif
  
  const char* SkXfermode::ModeName(Mode mode) {
      SkASSERT((unsigned) mode <= (unsigned)kLastMode);
      const char* gModeStrings[] = {
          "Clear", "Src", "Dst", "SrcOver", "DstOver", "SrcIn", "DstIn",
          "SrcOut", "DstOut", "SrcATop", "DstATop", "Xor", "Plus",
          "Modulate", "Screen", "Overlay", "Darken", "Lighten", "ColorDodge",
          "ColorBurn", "HardLight", "SoftLight", "Difference", "Exclusion",
          "Multiply", "Hue", "Saturation", "Color",  "Luminosity"
      };
      return gModeStrings[mode];
      SK_COMPILE_ASSERT(SK_ARRAY_COUNT(gModeStrings) == kLastMode + 1, mode_count);
  }
  
  #ifndef SK_IGNORE_TO_STRING
  void SkProcCoeffXfermode::toString(SkString* str) const {
      str->append("SkProcCoeffXfermode: ");
  
      str->append("mode: ");
      str->append(ModeName(fMode));
  
      static const char* gCoeffStrings[kCoeffCount] = {
          "Zero", "One", "SC", "ISC", "DC", "IDC", "SA", "ISA", "DA", "IDA"
      };
  
      str->append(" src: ");
      if (CANNOT_USE_COEFF == fSrcCoeff) {
          str->append("can't use");
      } else {
          str->append(gCoeffStrings[fSrcCoeff]);
      }
  
      str->append(" dst: ");
      if (CANNOT_USE_COEFF == fDstCoeff) {
          str->append("can't use");
      } else {
          str->append(gCoeffStrings[fDstCoeff]);
      }
  }
  #endif
  
  ///////////////////////////////////////////////////////////////////////////////
  
  class SkClearXfermode : public SkProcCoeffXfermode {
  public:
      static SkClearXfermode* Create(const ProcCoeff& rec) {
          return SkNEW_ARGS(SkClearXfermode, (rec));
      }
  
      virtual void xfer32(SkPMColor*, const SkPMColor*, int, const SkAlpha*) const SK_OVERRIDE;
      virtual void xferA8(SkAlpha*, const SkPMColor*, int, const SkAlpha*) const SK_OVERRIDE;
  
      SK_TO_STRING_OVERRIDE()
  
  private:
      SkClearXfermode(const ProcCoeff& rec) : SkProcCoeffXfermode(rec, kClear_Mode) {}
  
      typedef SkProcCoeffXfermode INHERITED;
  };
  
  void SkClearXfermode::xfer32(SkPMColor* SK_RESTRICT dst,
                               const SkPMColor* SK_RESTRICT, int count,
                               const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && count >= 0);
  
      if (NULL == aa) {
          memset(dst, 0, count << 2);
      } else {
          for (int i = count - 1; i >= 0; --i) {
              unsigned a = aa[i];
              if (0xFF == a) {
                  dst[i] = 0;
              } else if (a != 0) {
                  dst[i] = SkAlphaMulQ(dst[i], SkAlpha255To256(255 - a));
              }
          }
      }
  }
  void SkClearXfermode::xferA8(SkAlpha* SK_RESTRICT dst,
                               const SkPMColor* SK_RESTRICT, int count,
                               const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && count >= 0);
  
      if (NULL == aa) {
          memset(dst, 0, count);
      } else {
          for (int i = count - 1; i >= 0; --i) {
              unsigned a = aa[i];
              if (0xFF == a) {
                  dst[i] = 0;
              } else if (0 != a) {
                  dst[i] = SkAlphaMulAlpha(dst[i], 255 - a);
              }
          }
      }
  }
  
  #ifndef SK_IGNORE_TO_STRING
  void SkClearXfermode::toString(SkString* str) const {
      this->INHERITED::toString(str);
  }
  #endif
  
  ///////////////////////////////////////////////////////////////////////////////
  
  class SkSrcXfermode : public SkProcCoeffXfermode {
  public:
      static SkSrcXfermode* Create(const ProcCoeff& rec) {
          return SkNEW_ARGS(SkSrcXfermode, (rec));
      }
  
      virtual void xfer32(SkPMColor*, const SkPMColor*, int, const SkAlpha*) const SK_OVERRIDE;
      virtual void xferA8(SkAlpha*, const SkPMColor*, int, const SkAlpha*) const SK_OVERRIDE;
  
      SK_TO_STRING_OVERRIDE()
  
  private:
      SkSrcXfermode(const ProcCoeff& rec) : SkProcCoeffXfermode(rec, kSrc_Mode) {}
      typedef SkProcCoeffXfermode INHERITED;
  };
  
  void SkSrcXfermode::xfer32(SkPMColor* SK_RESTRICT dst,
                             const SkPMColor* SK_RESTRICT src, int count,
                             const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src && count >= 0);
  
      if (NULL == aa) {
          memcpy(dst, src, count << 2);
      } else {
          for (int i = count - 1; i >= 0; --i) {
              unsigned a = aa[i];
              if (a == 0xFF) {
                  dst[i] = src[i];
              } else if (a != 0) {
                  dst[i] = SkFourByteInterp(src[i], dst[i], a);
              }
          }
      }
  }
  
  void SkSrcXfermode::xferA8(SkAlpha* SK_RESTRICT dst,
                             const SkPMColor* SK_RESTRICT src, int count,
                             const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src && count >= 0);
  
      if (NULL == aa) {
          for (int i = count - 1; i >= 0; --i) {
              dst[i] = SkToU8(SkGetPackedA32(src[i]));
          }
      } else {
          for (int i = count - 1; i >= 0; --i) {
              unsigned a = aa[i];
              if (0 != a) {
                  unsigned srcA = SkGetPackedA32(src[i]);
                  if (a == 0xFF) {
                      dst[i] = SkToU8(srcA);
                  } else {
                      dst[i] = SkToU8(SkAlphaBlend(srcA, dst[i], a));
                  }
              }
          }
      }
  }
  #ifndef SK_IGNORE_TO_STRING
  void SkSrcXfermode::toString(SkString* str) const {
      this->INHERITED::toString(str);
  }
  #endif
  
  ///////////////////////////////////////////////////////////////////////////////
  
  class SkDstInXfermode : public SkProcCoeffXfermode {
  public:
      static SkDstInXfermode* Create(const ProcCoeff& rec) {
          return SkNEW_ARGS(SkDstInXfermode, (rec));
      }
  
      virtual void xfer32(SkPMColor*, const SkPMColor*, int, const SkAlpha*) const SK_OVERRIDE;
  
      SK_TO_STRING_OVERRIDE()
  
  private:
      SkDstInXfermode(const ProcCoeff& rec) : SkProcCoeffXfermode(rec, kDstIn_Mode) {}
  
      typedef SkProcCoeffXfermode INHERITED;
  };
  
  void SkDstInXfermode::xfer32(SkPMColor* SK_RESTRICT dst,
                               const SkPMColor* SK_RESTRICT src, int count,
                               const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src);
  
      if (count <= 0) {
          return;
      }
      if (aa) {
          return this->INHERITED::xfer32(dst, src, count, aa);
      }
  
      do {
          unsigned a = SkGetPackedA32(*src);
          *dst = SkAlphaMulQ(*dst, SkAlpha255To256(a));
          dst++;
          src++;
      } while (--count != 0);
  }
  
  #ifndef SK_IGNORE_TO_STRING
  void SkDstInXfermode::toString(SkString* str) const {
      this->INHERITED::toString(str);
  }
  #endif
  
  ///////////////////////////////////////////////////////////////////////////////
  
  class SkDstOutXfermode : public SkProcCoeffXfermode {
  public:
      static SkDstOutXfermode* Create(const ProcCoeff& rec) {
          return SkNEW_ARGS(SkDstOutXfermode, (rec));
      }
  
      virtual void xfer32(SkPMColor*, const SkPMColor*, int, const SkAlpha*) const SK_OVERRIDE;
  
      SK_TO_STRING_OVERRIDE()
  
  private:
      SkDstOutXfermode(const ProcCoeff& rec) : SkProcCoeffXfermode(rec, kDstOut_Mode) {}
  
      typedef SkProcCoeffXfermode INHERITED;
  };
  
  void SkDstOutXfermode::xfer32(SkPMColor* SK_RESTRICT dst,
                                const SkPMColor* SK_RESTRICT src, int count,
                                const SkAlpha* SK_RESTRICT aa) const {
      SkASSERT(dst && src);
  
      if (count <= 0) {
          return;
      }
      if (aa) {
          return this->INHERITED::xfer32(dst, src, count, aa);
      }
  
      do {
          unsigned a = SkGetPackedA32(*src);
          *dst = SkAlphaMulQ(*dst, SkAlpha255To256(255 - a));
          dst++;
          src++;
      } while (--count != 0);
  }
  
  #ifndef SK_IGNORE_TO_STRING
  void SkDstOutXfermode::toString(SkString* str) const {
      this->INHERITED::toString(str);
  }
  #endif
  
  ///////////////////////////////////////////////////////////////////////////////
  
  extern SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec, SkXfermode::Mode mode);
  extern SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode);
  
  // Technically, can't be static and passed as a template parameter.  So we use anonymous namespace.
  namespace {
  SkXfermode* create_mode(int iMode) {
      SkXfermode::Mode mode = (SkXfermode::Mode)iMode;
  
      ProcCoeff rec = gProcCoeffs[mode];
      SkXfermodeProc pp = SkPlatformXfermodeProcFactory(mode);
      if (pp != NULL) {
          rec.fProc = pp;
      }
  
      SkXfermode* xfer = NULL;
      // check if we have a platform optim for that
      SkProcCoeffXfermode* xfm = SkPlatformXfermodeFactory(rec, mode);
      if (xfm != NULL) {
          xfer = xfm;
      } else {
          // All modes can in theory be represented by the ProcCoeff rec, since
          // it contains function ptrs. However, a few modes are both simple and
          // commonly used, so we call those out for their own subclasses here.
          switch (mode) {
              case SkXfermode::kClear_Mode:
                  xfer = SkClearXfermode::Create(rec);
                  break;
              case SkXfermode::kSrc_Mode:
                  xfer = SkSrcXfermode::Create(rec);
                  break;
              case SkXfermode::kSrcOver_Mode:
                  SkASSERT(false);    // should not land here
                  break;
              case SkXfermode::kDstIn_Mode:
                  xfer = SkDstInXfermode::Create(rec);
                  break;
              case SkXfermode::kDstOut_Mode:
                  xfer = SkDstOutXfermode::Create(rec);
                  break;
              default:
                  // no special-case, just rely in the rec and its function-ptrs
                  xfer = SkNEW_ARGS(SkProcCoeffXfermode, (rec, mode));
                  break;
          }
      }
      return xfer;
  }
  }  // namespace
  
  SK_DECLARE_STATIC_LAZY_PTR_ARRAY(SkXfermode, cached, SkXfermode::kLastMode + 1, create_mode);
  
  SkXfermode* SkXfermode::Create(Mode mode) {
      SkASSERT(SK_ARRAY_COUNT(gProcCoeffs) == kModeCount);
  
      if ((unsigned)mode >= kModeCount) {
          // report error
          return NULL;
      }
  
      // Skia's "default" mode is srcover. NULL in SkPaint is interpreted as srcover
      // so we can just return NULL from the factory.
      if (kSrcOver_Mode == mode) {
          return NULL;
      }
  
      return SkSafeRef(cached[mode]);
  }
  
  SkXfermodeProc SkXfermode::GetProc(Mode mode) {
      SkXfermodeProc  proc = NULL;
      if ((unsigned)mode < kModeCount) {
          proc = gProcCoeffs[mode].fProc;
      }
      return proc;
  }
  
  bool SkXfermode::ModeAsCoeff(Mode mode, Coeff* src, Coeff* dst) {
      SkASSERT(SK_ARRAY_COUNT(gProcCoeffs) == kModeCount);
  
      if ((unsigned)mode >= (unsigned)kModeCount) {
          // illegal mode parameter
          return false;
      }
  
      const ProcCoeff& rec = gProcCoeffs[mode];
  
      if (CANNOT_USE_COEFF == rec.fSC) {
          return false;
      }
  
      SkASSERT(CANNOT_USE_COEFF != rec.fDC);
      if (src) {
          *src = rec.fSC;
      }
      if (dst) {
          *dst = rec.fDC;
      }
      return true;
  }
  
  bool SkXfermode::AsMode(const SkXfermode* xfer, Mode* mode) {
      if (NULL == xfer) {
          if (mode) {
              *mode = kSrcOver_Mode;
          }
          return true;
      }
      return xfer->asMode(mode);
  }
  
  bool SkXfermode::AsCoeff(const SkXfermode* xfer, Coeff* src, Coeff* dst) {
      if (NULL == xfer) {
          return ModeAsCoeff(kSrcOver_Mode, src, dst);
      }
      return xfer->asCoeff(src, dst);
  }
  
  bool SkXfermode::IsMode(const SkXfermode* xfer, Mode mode) {
      // if xfer==null then the mode is srcover
      Mode m = kSrcOver_Mode;
      if (xfer && !xfer->asMode(&m)) {
          return false;
      }
      return mode == m;
  }
  
  ///////////////////////////////////////////////////////////////////////////////
  //////////// 16bit xfermode procs
  
  #ifdef SK_DEBUG
  static bool require_255(SkPMColor src) { return SkGetPackedA32(src) == 0xFF; }
  static bool require_0(SkPMColor src) { return SkGetPackedA32(src) == 0; }
  #endif
  
  static uint16_t src_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      return SkPixel32ToPixel16(src);
  }
  
  static uint16_t dst_modeproc16(SkPMColor src, uint16_t dst) {
      return dst;
  }
  
  static uint16_t srcover_modeproc16_0(SkPMColor src, uint16_t dst) {
      SkASSERT(require_0(src));
      return dst;
  }
  
  static uint16_t srcover_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      return SkPixel32ToPixel16(src);
  }
  
  static uint16_t dstover_modeproc16_0(SkPMColor src, uint16_t dst) {
      SkASSERT(require_0(src));
      return dst;
  }
  
  static uint16_t dstover_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      return dst;
  }
  
  static uint16_t srcin_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      return SkPixel32ToPixel16(src);
  }
  
  static uint16_t dstin_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      return dst;
  }
  
  static uint16_t dstout_modeproc16_0(SkPMColor src, uint16_t dst) {
      SkASSERT(require_0(src));
      return dst;
  }
  
  static uint16_t srcatop_modeproc16(SkPMColor src, uint16_t dst) {
      unsigned isa = 255 - SkGetPackedA32(src);
  
      return SkPackRGB16(
             SkPacked32ToR16(src) + SkAlphaMulAlpha(SkGetPackedR16(dst), isa),
             SkPacked32ToG16(src) + SkAlphaMulAlpha(SkGetPackedG16(dst), isa),
             SkPacked32ToB16(src) + SkAlphaMulAlpha(SkGetPackedB16(dst), isa));
  }
  
  static uint16_t srcatop_modeproc16_0(SkPMColor src, uint16_t dst) {
      SkASSERT(require_0(src));
      return dst;
  }
  
  static uint16_t srcatop_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      return SkPixel32ToPixel16(src);
  }
  
  static uint16_t dstatop_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      return dst;
  }
  
  /*********
      darken and lighten boil down to this.
  
      darken  = (1 - Sa) * Dc + min(Sc, Dc)
      lighten = (1 - Sa) * Dc + max(Sc, Dc)
  
      if (Sa == 0) these become
          darken  = Dc + min(0, Dc) = 0
          lighten = Dc + max(0, Dc) = Dc
  
      if (Sa == 1) these become
          darken  = min(Sc, Dc)
          lighten = max(Sc, Dc)
  */
  
  static uint16_t darken_modeproc16_0(SkPMColor src, uint16_t dst) {
      SkASSERT(require_0(src));
      return 0;
  }
  
  static uint16_t darken_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      unsigned r = SkFastMin32(SkPacked32ToR16(src), SkGetPackedR16(dst));
      unsigned g = SkFastMin32(SkPacked32ToG16(src), SkGetPackedG16(dst));
      unsigned b = SkFastMin32(SkPacked32ToB16(src), SkGetPackedB16(dst));
      return SkPackRGB16(r, g, b);
  }
  
  static uint16_t lighten_modeproc16_0(SkPMColor src, uint16_t dst) {
      SkASSERT(require_0(src));
      return dst;
  }
  
  static uint16_t lighten_modeproc16_255(SkPMColor src, uint16_t dst) {
      SkASSERT(require_255(src));
      unsigned r = SkMax32(SkPacked32ToR16(src), SkGetPackedR16(dst));
      unsigned g = SkMax32(SkPacked32ToG16(src), SkGetPackedG16(dst));
      unsigned b = SkMax32(SkPacked32ToB16(src), SkGetPackedB16(dst));
      return SkPackRGB16(r, g, b);
  }
  
  struct Proc16Rec {
      SkXfermodeProc16    fProc16_0;
      SkXfermodeProc16    fProc16_255;
      SkXfermodeProc16    fProc16_General;
  };
  
  static const Proc16Rec gModeProcs16[] = {
      { NULL,                 NULL,                   NULL            }, // CLEAR
      { NULL,                 src_modeproc16_255,     NULL            },
      { dst_modeproc16,       dst_modeproc16,         dst_modeproc16  },
      { srcover_modeproc16_0, srcover_modeproc16_255, NULL            },
      { dstover_modeproc16_0, dstover_modeproc16_255, NULL            },
      { NULL,                 srcin_modeproc16_255,   NULL            },
      { NULL,                 dstin_modeproc16_255,   NULL            },
      { NULL,                 NULL,                   NULL            },// SRC_OUT
      { dstout_modeproc16_0,  NULL,                   NULL            },
      { srcatop_modeproc16_0, srcatop_modeproc16_255, srcatop_modeproc16  },
      { NULL,                 dstatop_modeproc16_255, NULL            },
      { NULL,                 NULL,                   NULL            }, // XOR
  
      { NULL,                 NULL,                   NULL            }, // plus
      { NULL,                 NULL,                   NULL            }, // modulate
      { NULL,                 NULL,                   NULL            }, // screen
      { NULL,                 NULL,                   NULL            }, // overlay
      { darken_modeproc16_0,  darken_modeproc16_255,  NULL            }, // darken
      { lighten_modeproc16_0, lighten_modeproc16_255, NULL            }, // lighten
      { NULL,                 NULL,                   NULL            }, // colordodge
      { NULL,                 NULL,                   NULL            }, // colorburn
      { NULL,                 NULL,                   NULL            }, // hardlight
      { NULL,                 NULL,                   NULL            }, // softlight
      { NULL,                 NULL,                   NULL            }, // difference
      { NULL,                 NULL,                   NULL            }, // exclusion
      { NULL,                 NULL,                   NULL            }, // multiply
      { NULL,                 NULL,                   NULL            }, // hue
      { NULL,                 NULL,                   NULL            }, // saturation
      { NULL,                 NULL,                   NULL            }, // color
      { NULL,                 NULL,                   NULL            }, // luminosity
  };
  
  SkXfermodeProc16 SkXfermode::GetProc16(Mode mode, SkColor srcColor) {
      SkXfermodeProc16  proc16 = NULL;
      if ((unsigned)mode < kModeCount) {
          const Proc16Rec& rec = gModeProcs16[mode];
          unsigned a = SkColorGetA(srcColor);
  
          if (0 == a) {
              proc16 = rec.fProc16_0;
          } else if (255 == a) {
              proc16 = rec.fProc16_255;
          } else {
              proc16 = rec.fProc16_General;
          }
      }
      return proc16;
  }
  
  SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkXfermode)
      SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkProcCoeffXfermode)
  SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END
  