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 045117552626b55373074c6fa3c94d3b02295c9e..6496ef12de863ff374f13b80bdf8fb87a7e95888 100644
--- a/include/core/SkColorSpace.h
+++ b/include/core/SkColorSpace.h
@@ -13,6 +13,44 @@
 
 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:
 
@@ -44,9 +82,13 @@ public:
     };
 
     /**
-     *  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.