SoftLight with SkPMFloat

src/core/Sk4pxXfermode.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef Sk4pxXfermode_DEFINED
 #define Sk4pxXfermode_DEFINED
 
@@ skipping 123 matching lines @@
     auto srcover = s + d*isa,
          dstover = d + s*ida,
          otherwise = sa*(da-Sk4f::Min(da, (da-d)*sa*s.approxInvert())) + s*ida + d*isa;
 
     // Order matters here, preferring d==da over s==0.
     auto colors = (d ==      da).thenElse(dstover,
                   (s == Sk4f(0)).thenElse(srcover,
                                           otherwise));
     return srcover * SkPMFloat(1,0,0,0) + colors * SkPMFloat(0,1,1,1);
 }
+XFERMODE(SoftLight) {
+    auto sa = s.alphas(),
+         da = d.alphas(),
+         isa = Sk4f(1)-sa,
+         ida = Sk4f(1)-da;
+
+    // Some common terms.
+    auto m  = (da > Sk4f(0)).thenElse(d / da, Sk4f(0)),
+         s2 = Sk4f(2)*s,
+         m4 = Sk4f(4)*m;
+
+    // The logic forks three ways:
+    //    1. dark src?
+    //    2. light src, dark dst?
+    //    3. light src, light dst?
+    auto darkSrc = d*(sa + (s2 - sa)*(Sk4f(1) - m)),        // Used in case 1.
+         darkDst = (m4*m4 + m4)*(m - Sk4f(1)) + Sk4f(7)*m,  // Used in case 2.
+         liteDst = m.sqrt() - m,                            // Used in case 3.
+         liteSrc = d*sa + da*(s2-sa)*(Sk4f(4)*d <= da).thenElse(darkDst, liteDst); // Case 2 or 3?
+
+    auto alpha  = s + d*isa;
+    auto colors = s*ida + d*isa + (s2 <= sa).thenElse(darkSrc, liteSrc);           // Case 1 or 2/3?
+
+    return alpha * SkPMFloat(1,0,0,0) + colors * SkPMFloat(0,1,1,1);
+}
 #undef XFERMODE
 
 // A reasonable fallback mode for doing AA is to simply apply the transfermode first,
 // then linearly interpolate the AA.
 template <typename Mode>
 static Sk4px xfer_aa(const Sk4px& s, const Sk4px& d, const Sk4px& aa) {
     Sk4px bw = Mode::Xfer(s, d);
     return (bw * aa + d * aa.inv()).div255();
 }
 
@@ skipping 83 matching lines @@
         case SkXfermode::kDifference_Mode: return SkT4pxXfermode<Difference>::Create(rec);
         case SkXfermode::kExclusion_Mode:  return SkT4pxXfermode<Exclusion>::Create(rec);
 #if !defined(SK_SUPPORT_LEGACY_XFERMODES)  // For staging in Chrome (layout tests).
         case SkXfermode::kHardLight_Mode:  return SkT4pxXfermode<HardLight>::Create(rec);
         case SkXfermode::kOverlay_Mode:    return SkT4pxXfermode<Overlay>::Create(rec);
         case SkXfermode::kDarken_Mode:     return SkT4pxXfermode<Darken>::Create(rec);
         case SkXfermode::kLighten_Mode:    return SkT4pxXfermode<Lighten>::Create(rec);
 
         case SkXfermode::kColorDodge_Mode: return SkTPMFloatXfermode<ColorDodge>::Create(rec);
         case SkXfermode::kColorBurn_Mode:  return SkTPMFloatXfermode<ColorBurn>::Create(rec);
+        case SkXfermode::kSoftLight_Mode:  return SkTPMFloatXfermode<SoftLight>::Create(rec);
 #endif
         default: break;
     }
 #endif
     return nullptr;
 }
 
 } // namespace
 
 #endif//Sk4pxXfermode_DEFINED