starter kit for colorspaces

src/core/SkColorSpace.cpp

Index: src/core/SkColorSpace.cpp
diff --git a/src/core/SkColorSpace.cpp b/src/core/SkColorSpace.cpp
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+++ b/src/core/SkColorSpace.cpp
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+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkAtomics.h"
+#include "SkColorSpace.h"
+
+static inline bool SkFloatIsFinite(float x) { return 0 == x * 0; }
+
+//
+// SkFloat3x3
+//
+// In memory order, values are a, b, c, d, e, f, g, h, i
+//
+// When applied to a color component vector (e.g. [ r, r, r ] or [ g, g, g ] we do
+//
+// [ r r r ] * [ a b c ] + [ g g g ] * [ d e f ] + [ b b b ] * [ g h i ]
+//
+// Thus in our point-on-the-right notation, the matrix looks like
+//
+// [ a d g ]   [ r ]
+// [ b e h ] * [ g ]
+// [ c f i ]   [ b ]
+//
+static SkFloat3x3 concat(const SkFloat3x3& left, const SkFloat3x3& rite) {
+    SkFloat3x3 result;
+    for (int row = 0; row < 3; ++row) {
+        for (int col = 0; col < 3; ++col) {
+            double tmp = 0;
+            for (int i = 0; i < 3; ++i) {
+                tmp += (double)left.fMat[row + i * 3] * rite.fMat[i + col * 3];
+            }
+            result.fMat[row + col * 3] = (double)tmp;
+        }
+    }
+    return result;
+}
+
+static double det(const SkFloat3x3& m) {
+    return (double)m.fMat[0] * m.fMat[4] * m.fMat[8] +
+           (double)m.fMat[3] * m.fMat[7] * m.fMat[2] +
+           (double)m.fMat[6] * m.fMat[1] * m.fMat[5] -
+           (double)m.fMat[0] * m.fMat[7] * m.fMat[5] -
+           (double)m.fMat[3] * m.fMat[1] * m.fMat[8] -
+           (double)m.fMat[6] * m.fMat[4] * m.fMat[2];
+}
+
+static double det2x2(const SkFloat3x3& m, int a, int b, int c, int d) {
+    return (double)m.fMat[a] * m.fMat[b] - (double)m.fMat[c] * m.fMat[d];
+}
+
+static SkFloat3x3 invert(const SkFloat3x3& m) {
+    double d = det(m);
+    SkASSERT(SkFloatIsFinite((float)d));
+    double scale = 1 / d;
+    SkASSERT(SkFloatIsFinite((float)scale));
+
+    return {{
+        (float)(scale * det2x2(m, 4, 8, 5, 7)),
+        (float)(scale * det2x2(m, 7, 2, 8, 1)),
+        (float)(scale * det2x2(m, 1, 5, 2, 4)),
+
+        (float)(scale * det2x2(m, 6, 5, 8, 3)),
+        (float)(scale * det2x2(m, 0, 8, 2, 6)),
+        (float)(scale * det2x2(m, 3, 2, 5, 0)),
+
+        (float)(scale * det2x2(m, 3, 7, 4, 6)),
+        (float)(scale * det2x2(m, 6, 1, 7, 0)),
+        (float)(scale * det2x2(m, 0, 4, 1, 3)),
+    }};
+}
+
+void SkFloat3::dump() const {
+    SkDebugf("[%7.4f %7.4f %7.4f]\n", fVec[0], fVec[1], fVec[2]);
+}
+
+void SkFloat3x3::dump() const {
+    SkDebugf("[%7.4f %7.4f %7.4f] [%7.4f %7.4f %7.4f] [%7.4f %7.4f %7.4f]\n",
+             fMat[0], fMat[1], fMat[2],
+             fMat[3], fMat[4], fMat[5],
+             fMat[6], fMat[7], fMat[8]);
+}
+
+//////////////////////////////////////////////////////////////////////////////////////////////////
+
+static int32_t gUniqueColorSpaceID;
+
+SkColorSpace::SkColorSpace(const SkFloat3x3& toXYZD50, const SkFloat3& gamma, Named named)
+    : fToXYZD50(toXYZD50)
+    , fGamma(gamma)
+    , fUniqueID(sk_atomic_inc(&gUniqueColorSpaceID))
+    , fNamed(named)
+{
+    for (int i = 0; i < 3; ++i) {
+        SkASSERT(SkFloatIsFinite(gamma.fVec[i]));
+        for (int j = 0; j < 3; ++j) {
+            SkASSERT(SkFloatIsFinite(toXYZD50.fMat[3*i + j]));
+        }
+    }
+}
+
+SkColorSpace* SkColorSpace::NewRGB(const SkFloat3x3& toXYZD50, const SkFloat3& gamma) {
+    for (int i = 0; i < 3; ++i) {
+        if (!SkFloatIsFinite(gamma.fVec[i]) || gamma.fVec[i] < 0) {
+            return nullptr;
+        }
+        for (int j = 0; j < 3; ++j) {
+            if (!SkFloatIsFinite(toXYZD50.fMat[3*i + j])) {
+                return nullptr;
+            }
+        }
+    }
+
+    // check the matrix for invertibility
+    float d = det(toXYZD50);
+    if (!SkFloatIsFinite(d) || !SkFloatIsFinite(1 / d)) {
+        return nullptr;
+    }
+
+    return new SkColorSpace(toXYZD50, gamma, kUnknown_Named);
+}
+
+void SkColorSpace::dump() const {
+    fToXYZD50.dump();
+    fGamma.dump();
+}
+
+//////////////////////////////////////////////////////////////////////////////////////////////////
+
+const SkFloat3   gDevice_gamma {{ 0, 0, 0 }};
+const SkFloat3x3 gDevice_toXYZD50 {{
+    1, 0, 0,
+    0, 1, 0,
+    0, 0, 1
+}};
+
+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
+    0.1430f, 0.0606f, 0.7139f,    // * B
+}};
+
+SkColorSpace* SkColorSpace::NewNamed(Named named) {
+    switch (named) {
+        case kDevice_Named:
+            return new SkColorSpace(gDevice_toXYZD50, gDevice_gamma, kDevice_Named);
+        case kSRGB_Named:
+            return new SkColorSpace(gSRGB_toXYZD50, gSRGB_gamma, kSRGB_Named);
+        default:
+            break;
+    }
+    return nullptr;
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+SkColorSpace::Result SkColorSpace::Concat(const SkColorSpace* src, const SkColorSpace* dst,
+                                          SkFloat3x3* result) {
+    if (!src || !dst || (src->named() == kDevice_Named) || (src->named() == dst->named())) {
+        if (result) {
+            *result = {{ 1, 0, 0, 0, 1, 0, 0, 0, 1 }};
+        }
+        return kIdentity_Result;
+    }
+    if (result) {
+        *result = concat(src->fToXYZD50, invert(dst->fToXYZD50));
+    }
+    return kNormal_Result;
+}
+
+#include "SkColor.h"
+#include "SkNx.h"
+
+void SkApply3x3ToPM4f(const SkFloat3x3& m, const SkPM4f src[], SkPM4f dst[], int count) {
+    SkASSERT(1 == SkPM4f::G);
+    SkASSERT(3 == SkPM4f::A);
+
+    Sk4f cr, cg, cb;
+    cg = Sk4f::Load(m.fMat + 3);
+    if (0 == SkPM4f::R) {
+        SkASSERT(2 == SkPM4f::B);
+        cr = Sk4f::Load(m.fMat + 0);
+        cb = Sk4f(m.fMat[6], m.fMat[7], m.fMat[8], 0);
+    } else {
+        SkASSERT(0 == SkPM4f::B);
+        SkASSERT(2 == SkPM4f::R);
+        cb = Sk4f::Load(m.fMat + 0);
+        cr = Sk4f(m.fMat[6], m.fMat[7], m.fMat[8], 0);
+    }
+    cr = cr * Sk4f(1, 1, 1, 0);
+    cg = cg * Sk4f(1, 1, 1, 0);
+    cb = cb * Sk4f(1, 1, 1, 0);
+
+    for (int i = 0; i < count; ++i) {
+        Sk4f r = Sk4f(src[i].fVec[SkPM4f::R]);
+        Sk4f g = Sk4f(src[i].fVec[SkPM4f::G]);
+        Sk4f b = Sk4f(src[i].fVec[SkPM4f::B]);
+        Sk4f a = Sk4f(0, 0, 0, src[i].fVec[SkPM4f::A]);
+        (cr * r + cg * g + cb * b + a).store(&dst[i]);
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+void SkColorSpace::Test() {
+    SkFloat3x3 mat {{ 2, 0, 0, 0, 3, 0, 0, 0, 4 }};
+    SkFloat3x3 inv = invert(mat);
+    mat.dump();
+    inv.dump();
+    concat(mat, inv).dump();
+    concat(inv, mat).dump();
+    SkDebugf("\n");
+
+    mat = gSRGB_toXYZD50;
+    inv = invert(mat);
+    mat.dump();
+    inv.dump();
+    concat(mat, inv).dump();
+    concat(inv, mat).dump();
+    SkDebugf("\n");
+
+    SkAutoTUnref<SkColorSpace> cs0(SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named));
+    SkAutoTUnref<SkColorSpace> cs1(SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named));
+
+    cs0->dump();
+    cs1->dump();
+    SkFloat3x3 xform;
+    (void)SkColorSpace::Concat(cs0, cs1, &xform);
+    xform.dump();
+    SkDebugf("\n");
+}
+
+// D65 white point of Rec.  709 [8] are:
+//
+// D65 white-point in unit luminance XYZ = 0.9505, 1.0000, 1.0890
+//
+//          R           G           B           white
+//   x      0.640       0.300       0.150       0.3127
+//   y      0.330       0.600       0.060       0.3290
+//   z      0.030       0.100       0.790       0.3582