Add SkColorSpaceTransferFn to SkColorSpace

include/core/SkColorSpace.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkColorSpace_DEFINED
 #define SkColorSpace_DEFINED
 
@@ skipping 11 matching lines @@
     float fBX, fBY;
     float fWX, fWY;
 
     /**
      *  Convert primaries and a white point to a toXYZD50 matrix, the preferred color gamut
      *  representation of SkColorSpace.
      */
     bool toXYZD50(SkMatrix44* toXYZD50) const;
 };
 
+/**
+ *  Contains the coefficients for a common transfer function equation, specified as
+ *  a transformation from a curved space to linear.
+ *
+ *  LinearVal = E*InputVal + F        , for 0.0f <= InputVal <  D
+ *  LinearVal = (A*InputVal + B)^G + C, for D    <= InputVal <= 1.0f
+ *
+ *  Function is undefined if InputVal is not in [ 0.0f, 1.0f ].
+ *  Resulting LinearVals must be in [ 0.0f, 1.0f ].
+ *  Function must be positive and increasing.
+ */
+struct SK_API SkColorSpaceTransferFn {
+    float fG;
+    float fA;
+    float fB;
+    float fC;
+    float fD;
+    float fE;
+    float fF;
+};
+
 class SK_API SkColorSpace : public SkRefCnt {
 public:
 
     /**
      *  Common, named profiles that we can recognize.
      */
     enum Named : uint8_t {
         /**
          *  By far the most common color space.
          *  This is the default space for images, unmarked content, and monitors.
@@ skipping 19 matching lines @@
         /**
          *  Transfer function is the canonical sRGB curve, which has a short linear segment
          *  followed by a 2.4f exponential.
          */
         kSRGB_RenderTargetGamma,
     };
 
     /**
      *  Create an SkColorSpace from a transfer function and a color gamut.
      *
-     *  Transfer function is specified as linear or sRGB.
+     *  Transfer function can be specified as a render target or as the coefficients to an equation.
      *  Gamut is specified using the matrix transformation to XYZ D50.
      */
     static sk_sp<SkColorSpace> NewRGB(RenderTargetGamma gamma, const SkMatrix44& toXYZD50);
+    static sk_sp<SkColorSpace> NewRGB(const SkColorSpaceTransferFn& coeffs,
+                                      const SkMatrix44& toXYZD50);
 
     /**
      *  Create a common, named SkColorSpace.
      */
     static sk_sp<SkColorSpace> NewNamed(Named);
 
     /**
      *  Create an SkColorSpace from an ICC profile.
      */
     static sk_sp<SkColorSpace> NewICC(const void*, size_t);
@@ skipping 31 matching lines @@
      *  If both are null, we return true.  If one is null and the other is not, we return false.
      *  If both are non-null, we do a deeper compare.
      */
     static bool Equals(const SkColorSpace* src, const SkColorSpace* dst);
 
 protected:
     SkColorSpace() {}
 };
 
 #endif