Add SkColorSpacePrimaries to help with making D50 matrices

include/core/SkColorSpace.h

Index: include/core/SkColorSpace.h
diff --git a/include/core/SkColorSpace.h b/include/core/SkColorSpace.h
index 58095775e4b75e2b9f7a12970f173d5d7886a4f7..c4b34e844f538f88db48b14bd06e08ad42a3d56d 100644
--- a/include/core/SkColorSpace.h
+++ b/include/core/SkColorSpace.h
@@ -53,9 +53,42 @@ public:
     };
 
     /**
-     *  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.