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
 
@@ skipping 35 matching lines @@
          */
         kNonStandard_GammaNamed,
 
         /**
          *  To be used by UMA code only.  ICC profiles lacks valid gamma representation.
          */
         kInvalid_GammaNamed,
     };
 
     /**
-     *  Create an SkColorSpace from the src gamma and a transform from src gamut to D50 XYZ.
+     *  Contains the coefficients for a common transfer function equation.
+     */
+    struct GammaCoefficients {
+        //     Y = (aX + b)^g + c  for X >= d
+        //     Y = eX + f          otherwise
+        float                    fG;
+        float                    fA;
+        float                    fB;
+        float                    fC;
+        float                    fD;
+        float                    fE;
+        float                    fF;
+    };
+
+    /**
+     *  Describes a color gamut with primaries and a white point.
+     */
+    struct Primaries {
+        float fRX, fRY;
+        float fGX, fGY;
+        float fBX, fBY;
+        float fWX, fWY;
+    };
+
+    /**
+     *  Create an SkColorSpace from a gamma transfer function and a gamut.
+     *
+     *  Gamma can be specified using an enum or the coefficients to an equation.
+     *  Gamut can specified using the to D50 matrix transformation or using a set
+     *  of primaries and a white point.
+     *
      */
     static sk_sp<SkColorSpace> NewRGB(GammaNamed gammaNamed, const SkMatrix44& toXYZD50);
+    static sk_sp<SkColorSpace> NewRGB(const GammaCoefficients& coeffs, const SkMatrix44& toXYZD50);
+    static sk_sp<SkColorSpace> NewRGB(GammaNamed gammaNamed, const Primaries& primaries);

[Brian Osman, 2016/09/02 15:37:52]

I already mentioned this to Matt, but this set of factories (and this one in
particular) will be super useful to me for testing. This format of data
(primaries w/ white point) is the easiest and canonical way to find/express
various gamuts. It bypasses all the problems with distributing (potentially
copyrighted) ICC profiles.

And for applications written in Skia, we're going to need to mix those gamuts
with other gammas - if someone wants to work in "DCI P3" for example, they're
still going to have to settle for the sRGB transfer function (in 8-bit) or
linear (in FP16), so this makes it even easier to directly construct any such
combination.

+    static sk_sp<SkColorSpace> NewRGB(const GammaCoefficients& coeffs, const Primaries& primaries);
 
     /**
      *  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 48 matching lines @@
 
 protected:
     SkColorSpace(GammaNamed gammaNamed, const SkMatrix44& toXYZD50, Named named);
 
     const GammaNamed fGammaNamed;
     const SkMatrix44 fToXYZD50;
     const Named      fNamed;
 };
 
 #endif