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 715cc403e3fe8fac354bf46d8ddde7c9e0fc11dc..8559d4e05ca5174c184c2c845b4b5405c4587278 100644
--- a/include/core/SkColorSpace.h
+++ b/include/core/SkColorSpace.h
@@ -13,6 +13,105 @@
 
 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;
+
+    enum Named {
+        kBT2020_Named,
+        kBT709_Named,
+    };
+
+    /**
+     *  Just a few examples.  Clients are free to fill in their own gamut.
+     */
+    SkPrimaries(Named named) {

[reed1, 2016/09/06 23:19:48]

like not inlined, right?

[msarett, 2016/09/07 14:01:20]

Yes, not here.

I've added a default constructor and improved the comment.

+        switch (named) {
+            case kBT2020_Named:
+                fRX = 0.708f;
+                fRY = 0.292f;
+                fGX = 0.170f;
+                fGY = 0.797f;
+                fBX = 0.131f;
+                fBY = 0.046f;
+                fWX = 0.3127f;
+                fWY = 0.3290f;
+                break;
+            case kBT709_Named:
+                fRX = 0.640f;
+                fRY = 0.330f;
+                fGX = 0.300f;
+                fGY = 0.600f;
+                fBX = 0.150f;
+                fBY = 0.060f;
+                fWX = 0.3127f;
+                fWY = 0.3290f;
+                break;
+        }
+    }
+};
+
+/**
+ *  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 SkTransferFn {
+
+    float fG;
+    float fA;
+    float fB;
+    float fC;
+    float fD;
+    float fE;
+    float fF;
+
+    enum Named {
+        kBT2020_Named,
+        kBT709_Named,
+        k2Dot2_Named,
+    };
+
+    /**
+     *  Just a few examples.  Clients are free to fill in their own function.
+     */
+    SkTransferFn(Named named) {
+        switch (named) {
+            case kBT2020_Named:
+            case kBT709_Named:
+                fG = (1.0f / 0.45f);
+                fA = (1.0f / 1.099296826809442f);
+                fB = (0.099296826809442f / 1.099296826809442f);
+                fC = 0.0f;
+                fD = 0.081f;
+                fE = (1.0f / 4.0f);
+                fF = 0.0f;
+                break;
+            case k2Dot2_Named:
+                fG = 2.2f;
+                fA = 1.0f;
+                fB = 0.0f;
+                fC = 0.0f;
+                fD = 0.0f;
+                fE = 0.0f;
+                fF = 0.0f;
+                break;
+        }
+    }
+};
+
 class SK_API SkColorSpace : public SkRefCnt {
 public:
 
@@ -44,9 +143,25 @@ public:
     };
 
     /**
-     *  Create an SkColorSpace from the src gamma and a transform from src gamut to D50 XYZ.
+     *  Convert primaries and a white point to a toXYZD50 matrix, the preferred color gamut
+     *  representation of SkColorSpace.
+     */
+    static bool PrimariesToXYZD50(SkMatrix44* /*toXYZD50*/, const SkPrimaries& /*primaries*/) {

[reed1, 2016/09/06 23:19:48]

can/should this be a method on primaries?

[msarett, 2016/09/07 14:01:20]

Yes, works for me.

+        // TODO: Implement this.
+        return false;
+    }
+
+    /**
+     *  Create an SkColorSpace from a transfer function and a gamut.
+     *
+     *  Transfer function 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 SkTransferFn& coeffs, const SkMatrix44& toXYZD50);
+    static sk_sp<SkColorSpace> NewRGB(GammaNamed gammaNamed, const SkPrimaries& primaries);
+    static sk_sp<SkColorSpace> NewRGB(const SkTransferFn& coeffs, const SkPrimaries& primaries);
 
     /**
      *  Create a common, named SkColorSpace.