Introduce SkGammas type to represent ICC gamma curves

src/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 17 matching lines @@
 
     void dump() const;
 };
 
 struct SkFloat3x3 {
     float fMat[9];
 
     void dump() const;
 };
 
-struct SkColorLookUpTable {
-    static const uint8_t kMaxChannels = 16;
+class SkColorSpace : public SkRefCnt {
+private:
+    struct SkGammaCurve {

[msarett, 2016/04/29 14:07:08]

Strange to have the private structs first, but I need to define SkGammaCurve
before SkGammas.

[scroggo, 2016/04/29 14:17:23]

Would forward declaring them fix this?

[msarett, 2016/04/29 14:44:12]

Unfortunately no, that doesn't work.

+        bool isValue() const { return 0.0f != fValue; }
+        bool isTable() const { return 0 != fTableSize; }

[scroggo, 2016/04/29 14:17:23]

It seems this does not do anything to protect from isValue and isTable returning
true?

[msarett, 2016/04/29 14:44:12]

Good point.  Now that this is private, that could only be a coding error.  I'll
add some asserts.

+        bool isParametric() const { return false; }
 
-    uint8_t                  fInputChannels;
-    uint8_t                  fOutputChannels;
-    uint8_t                  fGridPoints[kMaxChannels];
-    std::unique_ptr<float[]> fTable;
+        // We have three different ways to represent gamma.
+        // (1) A single value:
+        float                    fValue;
 
-    SkColorLookUpTable() {
-        memset(this, 0, sizeof(struct SkColorLookUpTable));
-    }
+        // (2) A lookup table:
+        uint32_t                 fTableSize;
+        std::unique_ptr<float[]> fTable;
 
-    SkColorLookUpTable(SkColorLookUpTable&& that)
-        : fInputChannels(that.fInputChannels)
-        , fOutputChannels(that.fOutputChannels)
-        , fTable(std::move(that.fTable))
-    {
-        memcpy(fGridPoints, that.fGridPoints, kMaxChannels);
-    }
-};
+        // (3) Parameters for a curve:
+        // FIXME (msarett): Handle parametric curves.
 
-class SkColorSpace : public SkRefCnt {
+        SkGammaCurve() {
+            memset(this, 0, sizeof(struct SkGammaCurve));
+        }
+
+        SkGammaCurve(float value)
+            : fValue(value)
+            , fTableSize(0)
+            , fTable(nullptr)
+        {}
+    };
+
+    struct SkColorLookUpTable {
+        static const uint8_t kMaxChannels = 16;
+
+        uint8_t                  fInputChannels;
+        uint8_t                  fOutputChannels;
+        uint8_t                  fGridPoints[kMaxChannels];
+        std::unique_ptr<float[]> fTable;
+
+        SkColorLookUpTable() {
+            memset(this, 0, sizeof(struct SkColorLookUpTable));
+        }
+    };
+
 public:
     enum Named {
         kUnknown_Named,
         kSRGB_Named,
     };
 
+    struct SkGammas {
+    public:
+        SkGammas(float red, float green, float blue)
+            : fRed(red)
+            , fGreen(green)
+            , fBlue(blue)
+        {}
+
+        SkGammas() {}
+
+        float red() const { return fRed.fValue; }

[msarett, 2016/04/29 14:07:08]

May not even need to expose these, but they are useful for testing.

[scroggo, 2016/04/29 14:17:23]

SkDEBUGCODE?

[msarett, 2016/04/29 14:44:12]

Good idea!

+        float green() const { return fGreen.fValue; }

[scroggo, 2016/04/29 14:17:23]

Is it okay to return fValue if !isValue()?

[msarett, 2016/04/29 14:44:12]

In that case, we return 0.0f.  This is a bit weird, though I'm not sure what
else to return.  It's probably better to just not have these APIs at all.

So I think this is another +1 to making them SkDEBUGCODE.

+        float blue() const { return fBlue.fValue; }
+
+    private:
+        SkGammaCurve fRed;
+        SkGammaCurve fGreen;
+        SkGammaCurve fBlue;
+
+        friend class SkColorSpace;
+    };
+
     /**
      *  Return a colorspace instance, given a 3x3 transform from linear_RGB to D50_XYZ
      *  and the src-gamma, return a ColorSpace
      */
-    static sk_sp<SkColorSpace> NewRGB(const SkFloat3x3& toXYZD50, const SkFloat3& gamma);
+    static sk_sp<SkColorSpace> NewRGB(const SkFloat3x3& toXYZD50, SkGammas gammas);
 
     static sk_sp<SkColorSpace> NewNamed(Named);
     static sk_sp<SkColorSpace> NewICC(const void*, size_t);
 
-    SkFloat3 gamma() const { return fGamma; }
+    const SkGammas& gammas() const { return fGammas; }
     SkFloat3x3 xyz() const { return fToXYZD50; }
     SkFloat3 xyzOffset() const { return fToXYZOffset; }
     Named named() const { return fNamed; }
     uint32_t uniqueID() const { return fUniqueID; }
 
 private:
-    SkColorSpace(const SkFloat3& gamma, const SkFloat3x3& toXYZ, Named);
 
-    SkColorSpace(SkColorLookUpTable colorLUT, const SkFloat3& gamma, const SkFloat3x3& toXYZ,
-                 const SkFloat3& toXYZOffset);
+    static bool LoadGammas(SkGammaCurve* gammas, uint32_t num, const uint8_t* src, size_t len);
+
+
+    static bool LoadColorLUT(SkColorLookUpTable* colorLUT, uint32_t inputChannels,
+                             uint32_t outputChannels, const uint8_t* src, size_t len);
+
+
+    static bool LoadA2B0(SkColorLookUpTable* colorLUT, SkGammas* gammas, SkFloat3x3* toXYZ,
+                         SkFloat3* toXYZOffset, const uint8_t* src, size_t len);
+
+    SkColorSpace(SkGammas gammas, const SkFloat3x3& toXYZ, Named);
+
+    SkColorSpace(SkColorLookUpTable colorLUT, SkGammas gammas,
+                 const SkFloat3x3& toXYZ, const SkFloat3& toXYZOffset);
 
     const SkColorLookUpTable fColorLUT;
-    const SkFloat3           fGamma;
+    const SkGammas           fGammas;
     const SkFloat3x3         fToXYZD50;
     const SkFloat3           fToXYZOffset;
 
     const uint32_t           fUniqueID;
     const Named              fNamed;
 };
 
 #endif