Introduce SkGammas type to represent ICC gamma curves

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1928123002

Committed: https://skia.googlesource.com/skia/+/7b2c6dd8c918209cb92e1338905d511c68da3eb2

Review-Url: https://codereview.chromium.org/1928123002

4 files changed, 163 insertions, 102 deletions

diff --git a/src/codec/SkPngCodec.cpp b/src/codec/SkPngCodec.cpp
index 1ad7f8006e..b34c80c6ed 100644
--- a/src/codec/SkPngCodec.cpp
+++ b/src/codec/SkPngCodec.cpp
@@ -210,7 +210,7 @@ sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
     png_fixed_point XYZ[9];
     SkFloat3x3 toXYZD50;
     png_fixed_point gamma;
-    SkFloat3 gammas;
+    SkColorSpace::SkGammas gammas;
     if (png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &XYZ[0], &XYZ[1], &XYZ[2], &XYZ[3], &XYZ[4],
             &XYZ[5], &XYZ[6], &XYZ[7], &XYZ[8])) {
 
@@ -225,16 +225,17 @@ sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
         }
 
         if (PNG_INFO_gAMA == png_get_gAMA_fixed(png_ptr, info_ptr, &gamma)) {
-            gammas.fVec[0] = gammas.fVec[1] = gammas.fVec[2] =
-                    png_inverted_fixed_point_to_float(gamma);
+            float value = png_inverted_fixed_point_to_float(gamma);
+            gammas = SkColorSpace::SkGammas(value, value, value);
+
         } else {
-            // If the image does not specify gamma, let's choose linear.  Should we default
-            // to sRGB?  Most images are intended to be sRGB (gamma = 2.2f).
-            gammas.fVec[0] = gammas.fVec[1] = gammas.fVec[2] = 1.0f;
+            // Default to sRGB (gamma = 2.2f) if the image has color space information,
+            // but does not specify gamma.
+            gammas = SkColorSpace::SkGammas(2.2f, 2.2f, 2.2f);
         }
 
 
-        return SkColorSpace::NewRGB(toXYZD50, gammas);
+        return SkColorSpace::NewRGB(toXYZD50, std::move(gammas));
     }
 
     // Last, check for gamma.
@@ -247,9 +248,10 @@ sk_sp<SkColorSpace> read_color_space(png_structp png_ptr, png_infop info_ptr) {
         toXYZD50.fMat[0] = toXYZD50.fMat[4] = toXYZD50.fMat[8] = 1.0f;
 
         // Set the gammas.
-        gammas.fVec[0] = gammas.fVec[1] = gammas.fVec[2] = png_inverted_fixed_point_to_float(gamma);
+        float value = png_inverted_fixed_point_to_float(gamma);
+        gammas = SkColorSpace::SkGammas(value, value, value);
 
-        return SkColorSpace::NewRGB(toXYZD50, gammas);
+        return SkColorSpace::NewRGB(toXYZD50, std::move(gammas));
     }
 
 #endif // LIBPNG >= 1.6
diff --git a/src/core/SkColorSpace.cpp b/src/core/SkColorSpace.cpp
index 43c424f1dc..54495de940 100644
--- a/src/core/SkColorSpace.cpp
+++ b/src/core/SkColorSpace.cpp
@@ -23,29 +23,28 @@ void SkFloat3x3::dump() const {
 
 static int32_t gUniqueColorSpaceID;
 
-SkColorSpace::SkColorSpace(const SkFloat3& gamma, const SkFloat3x3& toXYZD50, Named named)
-    : fGamma(gamma)
+SkColorSpace::SkColorSpace(SkGammas gammas, const SkFloat3x3& toXYZD50, Named named)
+    : fGammas(std::move(gammas))
     , fToXYZD50(toXYZD50)
     , fToXYZOffset({{ 0.0f, 0.0f, 0.0f }})
     , fUniqueID(sk_atomic_inc(&gUniqueColorSpaceID))
     , fNamed(named)
 {}
 
-SkColorSpace::SkColorSpace(SkColorLookUpTable colorLUT, const SkFloat3& gamma,
+SkColorSpace::SkColorSpace(SkColorLookUpTable colorLUT, SkGammas gammas,
                            const SkFloat3x3& toXYZD50, const SkFloat3& toXYZOffset)
     : fColorLUT(std::move(colorLUT))
-    , fGamma(gamma)
+    , fGammas(std::move(gammas))
     , fToXYZD50(toXYZD50)
     , fToXYZOffset(toXYZOffset)
     , fUniqueID(sk_atomic_inc(&gUniqueColorSpaceID))
     , fNamed(kUnknown_Named)
 {}
 
-sk_sp<SkColorSpace> SkColorSpace::NewRGB(const SkFloat3x3& toXYZD50, const SkFloat3& gamma) {
-    return sk_sp<SkColorSpace>(new SkColorSpace(gamma, toXYZD50, kUnknown_Named));
+sk_sp<SkColorSpace> SkColorSpace::NewRGB(const SkFloat3x3& toXYZD50, SkGammas gammas) {
+    return sk_sp<SkColorSpace>(new SkColorSpace(std::move(gammas), toXYZD50, kUnknown_Named));
 }
 
-const SkFloat3 gSRGB_gamma {{ 2.2f, 2.2f, 2.2f }};
 const SkFloat3x3 gSRGB_toXYZD50 {{
     0.4358f, 0.2224f, 0.0139f,    // * R
     0.3853f, 0.7170f, 0.0971f,    // * G
@@ -55,7 +54,8 @@ const SkFloat3x3 gSRGB_toXYZD50 {{
 sk_sp<SkColorSpace> SkColorSpace::NewNamed(Named named) {
     switch (named) {
         case kSRGB_Named:
-            return sk_sp<SkColorSpace>(new SkColorSpace(gSRGB_gamma, gSRGB_toXYZD50, kSRGB_Named));
+            return sk_sp<SkColorSpace>(new SkColorSpace(SkGammas(2.2f, 2.2f, 2.2f), gSRGB_toXYZD50,
+                                                        kSRGB_Named));
         default:
             break;
     }
@@ -264,9 +264,8 @@ bool load_xyz(float dst[3], const uint8_t* src, size_t len) {
 static const uint32_t kTAG_CurveType     = SkSetFourByteTag('c', 'u', 'r', 'v');
 static const uint32_t kTAG_ParaCurveType = SkSetFourByteTag('p', 'a', 'r', 'a');
 
-// FIXME (msarett):
-// We need to handle the possibility that the gamma curve does not correspond to 2.2f.
-static bool load_gammas(float* gammas, uint32_t numGammas, const uint8_t* src, size_t len) {
+bool SkColorSpace::LoadGammas(SkGammaCurve* gammas, uint32_t numGammas, const uint8_t* src,
+                              size_t len) {
     for (uint32_t i = 0; i < numGammas; i++) {
         if (len < 12) {
             // FIXME (msarett):
@@ -289,7 +288,7 @@ static bool load_gammas(float* gammas, uint32_t numGammas, const uint8_t* src, s
                     // Some tags require a gamma curve, but the author doesn't actually want
                     // to transform the data.  In this case, it is common to see a curve with
                     // a count of 0.
-                    gammas[i] = 1.0f;
+                    gammas[i].fValue = 1.0f;
                     break;
                 } else if (len < 12 + 2 * count) {
                     SkColorSpacePrintf("gamma tag is too small (%d bytes)", len);
@@ -298,27 +297,31 @@ static bool load_gammas(float* gammas, uint32_t numGammas, const uint8_t* src, s
 
                 const uint16_t* table = (const uint16_t*) (src + 12);
                 if (1 == count) {
-                    // Table entry is the exponent (bias 256).
+                    // The table entry is the gamma (with a bias of 256).
                     uint16_t value = read_big_endian_short((const uint8_t*) table);
-                    gammas[i] = value / 256.0f;
+                    gammas[i].fValue = value / 256.0f;
                     SkColorSpacePrintf("gamma %d %g\n", value, *gamma);
                     break;
                 }
 
-                // Print the interpolation table.  For now, we ignore this and guess 2.2f.
+                // Fill in the interpolation table.
+                // FIXME (msarett):
+                // We should recognize commonly occurring tables and just set gamma to 2.2f.
+                gammas[i].fTableSize = count;
+                gammas[i].fTable = std::unique_ptr<float[]>(new float[count]);
                 for (uint32_t j = 0; j < count; j++) {
-                    SkColorSpacePrintf("curve[%d] %d\n", j,
-                            read_big_endian_short((const uint8_t*) &table[j]));
+                    gammas[i].fTable[j] =
+                            (read_big_endian_short((const uint8_t*) &table[j])) / 65535.0f;
                 }
-
-                gammas[i] = 2.2f;
                 break;
             }
             case kTAG_ParaCurveType:
                 // Guess 2.2f.
+                // FIXME (msarett): Handle parametric curves.
                 SkColorSpacePrintf("parametric curve\n");
-                gammas[i] = 2.2f;
+                gammas[i].fValue = 2.2f;
 
+                // Determine the size of the parametric curve tag.
                 switch(read_big_endian_short(src + 8)) {
                     case 0:
                         tagBytes = 12 + 4;
@@ -358,28 +361,19 @@ static bool load_gammas(float* gammas, uint32_t numGammas, const uint8_t* src, s
         }
     }
 
-    // If all of the gammas we encounter are 1.0f, indicate that we failed to load gammas.
-    // There is no need to apply a gamma of 1.0f.
-    for (uint32_t i = 0; i < numGammas; i++) {
-        if (1.0f != gammas[i]) {
-            return true;
-        }
-    }
-
-    return false;
+    return true;
 }
 
 static const uint32_t kTAG_AtoBType = SkSetFourByteTag('m', 'A', 'B', ' ');
 
-bool load_color_lut(SkColorLookUpTable* colorLUT, uint32_t inputChannels, uint32_t outputChannels,
-        const uint8_t* src, size_t len) {
+bool SkColorSpace::LoadColorLUT(SkColorLookUpTable* colorLUT, uint32_t inputChannels,
+                                uint32_t outputChannels, const uint8_t* src, size_t len) {
     if (len < 20) {
         SkColorSpacePrintf("Color LUT tag is too small (%d bytes).", len);
         return false;
     }
 
-    SkASSERT(inputChannels <= SkColorLookUpTable::kMaxChannels &&
-             outputChannels <= SkColorLookUpTable::kMaxChannels);
+    SkASSERT(inputChannels <= SkColorLookUpTable::kMaxChannels && 3 == outputChannels);
     colorLUT->fInputChannels = inputChannels;
     colorLUT->fOutputChannels = outputChannels;
     uint32_t numEntries = 1;
@@ -441,8 +435,8 @@ bool load_matrix(SkFloat3x3* toXYZ, SkFloat3* toXYZOffset, const uint8_t* src, s
     return true;
 }
 
-bool load_a2b0(SkColorLookUpTable* colorLUT, SkFloat3* gamma, SkFloat3x3* toXYZ,
-        SkFloat3* toXYZOffset, const uint8_t* src, size_t len) {
+bool SkColorSpace::LoadA2B0(SkColorLookUpTable* colorLUT, SkGammas* gammas, SkFloat3x3* toXYZ,
+                            SkFloat3* toXYZOffset, const uint8_t* src, size_t len) {
     if (len < 32) {
         SkColorSpacePrintf("A to B tag is too small (%d bytes).", len);
         return false;
@@ -460,7 +454,7 @@ bool load_a2b0(SkColorLookUpTable* colorLUT, SkFloat3* gamma, SkFloat3x3* toXYZ,
     uint8_t inputChannels = src[8];
     uint8_t outputChannels = src[9];
     if (0 == inputChannels || inputChannels > SkColorLookUpTable::kMaxChannels ||
-            0 < outputChannels || outputChannels > SkColorLookUpTable::kMaxChannels) {
+            3 != outputChannels) {
         // The color LUT assumes that there are at most 16 input channels.  For RGB
         // profiles, output channels should be 3.
         SkColorSpacePrintf("Too many input or output channels in A to B tag.\n");
@@ -483,16 +477,16 @@ bool load_a2b0(SkColorLookUpTable* colorLUT, SkFloat3* gamma, SkFloat3x3* toXYZ,
 
     uint32_t offsetToColorLUT = read_big_endian_int(src + 24);
     if (0 != offsetToColorLUT && offsetToColorLUT < len) {
-        if (!load_color_lut(colorLUT, inputChannels, outputChannels, src + offsetToColorLUT,
-                len - offsetToColorLUT)) {
+        if (!SkColorSpace::LoadColorLUT(colorLUT, inputChannels, outputChannels,
+                                        src + offsetToColorLUT, len - offsetToColorLUT)) {
             SkColorSpacePrintf("Failed to read color LUT from A to B tag.\n");
         }
     }
 
     uint32_t offsetToMCurves = read_big_endian_int(src + 20);
     if (0 != offsetToMCurves && offsetToMCurves < len) {
-        if (!load_gammas(gamma->fVec, outputChannels, src + offsetToMCurves, len - offsetToMCurves))
-        {
+        if (!SkColorSpace::LoadGammas(&gammas->fRed, outputChannels, src + offsetToMCurves,
+                                      len - offsetToMCurves)) {
             SkColorSpacePrintf("Failed to read M curves from A to B tag.\n");
         }
     }
@@ -567,42 +561,39 @@ sk_sp<SkColorSpace> SkColorSpace::NewICC(const void* base, size_t len) {
 
                 // It is not uncommon to see missing or empty gamma tags.  This indicates
                 // that we should use unit gamma.
-                SkFloat3 gamma {{ 1.0f, 1.0f, 1.0f }};
+                SkGammas gammas;
                 r = ICCTag::Find(tags.get(), tagCount, kTAG_rTRC);
                 g = ICCTag::Find(tags.get(), tagCount, kTAG_gTRC);
                 b = ICCTag::Find(tags.get(), tagCount, kTAG_bTRC);
-                if (!r ||
-                    !load_gammas(&gamma.fVec[0], 1, r->addr((const uint8_t*) base), r->fLength))
-                {
+                if (!r || !SkColorSpace::LoadGammas(&gammas.fRed, 1,
+                                                    r->addr((const uint8_t*) base), r->fLength)) {
                     SkColorSpacePrintf("Failed to read R gamma tag.\n");
                 }
-                if (!g ||
-                    !load_gammas(&gamma.fVec[1], 1, g->addr((const uint8_t*) base), g->fLength))
-                {
+                if (!g || !SkColorSpace::LoadGammas(&gammas.fGreen, 1,
+                                                    g->addr((const uint8_t*) base), g->fLength)) {
                     SkColorSpacePrintf("Failed to read G gamma tag.\n");
                 }
-                if (!b ||
-                    !load_gammas(&gamma.fVec[2], 1, b->addr((const uint8_t*) base), b->fLength))
-                {
+                if (!b || !SkColorSpace::LoadGammas(&gammas.fBlue, 1,
+                                                    b->addr((const uint8_t*) base), b->fLength)) {
                     SkColorSpacePrintf("Failed to read B gamma tag.\n");
                 }
-                return SkColorSpace::NewRGB(toXYZ, gamma);
+                return SkColorSpace::NewRGB(toXYZ, std::move(gammas));
             }
 
             // Recognize color profile specified by A2B0 tag.
             const ICCTag* a2b0 = ICCTag::Find(tags.get(), tagCount, kTAG_A2B0);
             if (a2b0) {
                 SkColorLookUpTable colorLUT;
-                SkFloat3 gamma;
+                SkGammas gammas;
                 SkFloat3x3 toXYZ;
                 SkFloat3 toXYZOffset;
-                if (!load_a2b0(&colorLUT, &gamma, &toXYZ, &toXYZOffset,
-                        a2b0->addr((const uint8_t*) base), a2b0->fLength)) {
+                if (!SkColorSpace::LoadA2B0(&colorLUT, &gammas, &toXYZ, &toXYZOffset,
+                                            a2b0->addr((const uint8_t*) base), a2b0->fLength)) {
                     return_null("Failed to parse A2B0 tag");
                 }
 
-                return sk_sp<SkColorSpace>(new SkColorSpace(std::move(colorLUT), gamma, toXYZ,
-                                                            toXYZOffset));
+                return sk_sp<SkColorSpace>(new SkColorSpace(std::move(colorLUT), std::move(gammas),
+                                                            toXYZ, toXYZOffset));
             }
 
         }
diff --git a/src/core/SkColorSpace.h b/src/core/SkColorSpace.h
index 2b3b15fe95..a1ccf13fe0 100644
--- a/src/core/SkColorSpace.h
+++ b/src/core/SkColorSpace.h
@@ -35,57 +35,121 @@ struct SkFloat3x3 {
     void dump() const;
 };
 
-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));
-    }
-
-    SkColorLookUpTable(SkColorLookUpTable&& that)
-        : fInputChannels(that.fInputChannels)
-        , fOutputChannels(that.fOutputChannels)
-        , fTable(std::move(that.fTable))
-    {
-        memcpy(fGridPoints, that.fGridPoints, kMaxChannels);
-    }
-};
-
 class SkColorSpace : public SkRefCnt {
+private:
+    struct SkGammaCurve {
+        bool isValue() const {
+            bool result = (0.0f != fValue);
+            SkASSERT(!result || (0 == fTableSize));
+            return result;
+        }
+
+        bool isTable() const {
+            bool result = (0 != fTableSize);
+            SkASSERT(!result || (0.0f == fValue));
+            SkASSERT(!result || fTable);
+            return result;
+        }
+
+        bool isParametric() const { return false; }
+
+        // We have three different ways to represent gamma.
+        // (1) A single value:
+        float                    fValue;
+
+        // (2) A lookup table:
+        uint32_t                 fTableSize;
+        std::unique_ptr<float[]> fTable;
+
+        // (3) Parameters for a curve:
+        // FIXME (msarett): Handle parametric curves.
+
+        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() {}
+
+        SkDEBUGCODE(float red() const { return fRed.fValue; })
+        SkDEBUGCODE(float green() const { return fGreen.fValue; })
+        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;
 
diff --git a/tests/ColorSpaceTest.cpp b/tests/ColorSpaceTest.cpp
index 313eed86f1..e5ecbc8346 100644
--- a/tests/ColorSpaceTest.cpp
+++ b/tests/ColorSpaceTest.cpp
@@ -35,12 +35,14 @@ DEF_TEST(ColorSpaceParsePngICCProfile, r) {
     SkColorSpace* colorSpace = codec->getColorSpace();
     REPORTER_ASSERT(r, nullptr != colorSpace);
 
-    // No need to use almost equal here.  The color profile that we have extracted
-    // actually has a table of gammas.  And our current implementation guesses 2.2f.
-    SkFloat3 gammas = colorSpace->gamma();
-    REPORTER_ASSERT(r, 2.2f == gammas.fVec[0]);
-    REPORTER_ASSERT(r, 2.2f == gammas.fVec[1]);
-    REPORTER_ASSERT(r, 2.2f == gammas.fVec[2]);
+    // The color profile that we have extracted has represents gamma with a lookup table.
+    // So we expect the gamma value to be zero.
+#ifdef SK_DEBUG
+    const SkColorSpace::SkGammas& gammas = colorSpace->gammas();
+    REPORTER_ASSERT(r, 0.0f == gammas.red());
+    REPORTER_ASSERT(r, 0.0f == gammas.green());
+    REPORTER_ASSERT(r, 0.0f == gammas.blue());
+#endif
 
     // These nine values were extracted from the color profile in isolation (before
     // we embedded it in the png).  Here we check that we still extract the same values.
@@ -75,10 +77,12 @@ DEF_TEST(ColorSpaceParseJpegICCProfile, r) {
 
     // It's important to use almost equal here.  This profile sets gamma as
     // 563 / 256, which actually comes out to about 2.19922.
-    SkFloat3 gammas = colorSpace->gamma();
-    REPORTER_ASSERT(r, almost_equal(2.2f, gammas.fVec[0]));
-    REPORTER_ASSERT(r, almost_equal(2.2f, gammas.fVec[1]));
-    REPORTER_ASSERT(r, almost_equal(2.2f, gammas.fVec[2]));
+#ifdef SK_DEBUG
+    const SkColorSpace::SkGammas& gammas = colorSpace->gammas();
+    REPORTER_ASSERT(r, almost_equal(2.2f, gammas.red()));
+    REPORTER_ASSERT(r, almost_equal(2.2f, gammas.green()));
+    REPORTER_ASSERT(r, almost_equal(2.2f, gammas.blue()));
+#endif
 
     // These nine values were extracted from the color profile.  Until we know any
     // better, we'll assume these are the right values and test that we continue