Add SkColorSpacePrimaries to help with making D50 matrices

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
 
 #include "SkMatrix44.h"
 #include "SkRefCnt.h"
 
 class SkData;
 
+/**
+ *  Describes a color gamut with primaries and a white point.
+ */
+struct SK_API SkPrimaries {
+    float fRX, fRY;
+    float fGX, fGY;
+    float fBX, fBY;
+    float fWX, fWY;
+
+    /**
+     *  Convert primaries and a white point to a toXYZD50 matrix, the preferred color gamut
+     *  representation of SkColorSpace.
+     */
+    // TODO: Implement this.
+    static bool PrimariesToXYZD50(SkMatrix44* toXYZD50, const SkPrimaries& primaries);

[reed1, 2016/09/07 22:50:45]

nit: doesn't need to be static:

bool toXYZD50(SkMatrix44*) const;

[msarett, 2016/09/08 02:24:08]

Done.

+};
+
+/**
+ *  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 increasing.
+ */
+struct SK_API SkTransferFn {
+    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 11 matching lines @@
         kLinear_RenderTargetGamma,
 
         /**
          *  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 transform to D50 XYZ.
+     *  Create an SkColorSpace from a transfer function and a color gamut.
+     *
+     *  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 SkTransferFn& 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 38 matching lines @@
      */
     static bool Equals(const SkColorSpace* src, const SkColorSpace* dst);
 
 protected:
     SkColorSpace(const SkMatrix44& toXYZD50);
 
     const SkMatrix44 fToXYZD50;
 };
 
 #endif