Initial implementation of a SkColorSpace_A2B xform

src/core/SkColorSpaceXform_A2B.cpp

Index: src/core/SkColorSpaceXform_A2B.cpp
diff --git a/src/core/SkColorSpaceXform_A2B.cpp b/src/core/SkColorSpaceXform_A2B.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..4fe6eb458cd370d5703d37f94d963cdbbc727aa3
--- /dev/null
+++ b/src/core/SkColorSpaceXform_A2B.cpp
@@ -0,0 +1,346 @@
+/*
+ * 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 "SkColorSpaceXform_A2B.h"
+
+#include "SkColorPriv.h"
+#include "SkColorSpace_A2B.h"
+#include "SkColorSpace_XYZ.h"
+#include "SkColorSpacePriv.h"
+#include "SkColorSpaceXformPriv.h"
+#include "SkMakeUnique.h"
+#include "SkNx.h"
+#include "SkSRGB.h"
+#include "SkTypes.h"
+
+#include "SkRasterPipeline_opts.h"
+
+#define AI SK_ALWAYS_INLINE
+
+namespace {
+
+class ApplyParametric {
+public:
+    ApplyParametric(const SkColorSpaceTransferFn& fn)
+        : fFn(fn)
+    {}
+
+    float operator()(float x) const {
+        float y;
+        if (x >= fFn.fD) {
+            y = ::powf(fFn.fA * x + fFn.fB, fFn.fG) + fFn.fC;
+        } else {
+            y = fFn.fE * x + fFn.fF;
+        }
+        if (y >= 1.f) {
+            return 1.f;
+        } else if (y >= 0.f) {
+            return y;
+        }
+        return 0.f;
+    }
+
+private:
+    SkColorSpaceTransferFn fFn;
+};
+
+class ApplyTable {
+public:
+    ApplyTable(const float* table, int size)
+        : fTable(table)
+        , fSize(size)
+    {}
+
+    float operator()(float x) const {
+        return interp_lut(x, fTable, fSize);
+    }
+
+private:
+    const float* fTable;
+    int          fSize;
+};
+
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+bool SkColorSpaceXform_A2B::onApply(ColorFormat dstFormat, void* dst, ColorFormat srcFormat,
+                                    const void* src, int count, SkAlphaType alphaType) const {
+    SkRasterPipeline pipeline;
+    switch (srcFormat) {
+        case kBGRA_8888_ColorFormat:
+            pipeline.append(SkRasterPipeline::load_s_8888, &src);
+            pipeline.append(SkRasterPipeline::swap_rb);
+            break;
+        case kRGBA_8888_ColorFormat:
+            pipeline.append(SkRasterPipeline::load_s_8888, &src);
+            break;
+        default:
+            SkCSXformPrintf("F16/F32 source color format not supported\n");
+            return false;
+    }
+
+    pipeline.extend(fElementsPipeline);
+
+    if (kPremul_SkAlphaType == alphaType) {
+        pipeline.append(SkRasterPipeline::premul);
+    }
+
+    switch (dstFormat) {
+        case kBGRA_8888_ColorFormat:
+            pipeline.append(SkRasterPipeline::swap_rb);
+            pipeline.append(SkRasterPipeline::store_8888, &dst);
+            break;
+        case kRGBA_8888_ColorFormat:
+            pipeline.append(SkRasterPipeline::store_8888, &dst);
+            break;
+        case kRGBA_F16_ColorFormat:
+            if (!fLinearDstGamma) {
+                return false;
+            }
+            pipeline.append(SkRasterPipeline::store_f16, &dst);
+            break;
+        case kRGBA_F32_ColorFormat:
+            if (!fLinearDstGamma) {
+                return false;
+            }
+            pipeline.append(SkRasterPipeline::store_f32, &dst);
+            break;
+    }
+
+    auto p = pipeline.compile();
+
+    p(0, count);
+
+    return true;
+}
+
+static inline SkColorSpaceTransferFn value_to_parametric(float exp) {
+    return {exp, 1.f, 0.f, 0.f, 0.f, 0.f, 0.f};
+}
+
+static inline SkColorSpaceTransferFn gammanamed_to_parametric(SkGammaNamed gammaNamed) {
+    switch (gammaNamed) {
+        case kLinear_SkGammaNamed:
+            return value_to_parametric(1.f);
+        case kSRGB_SkGammaNamed:
+            return {2.4f, (1.f / 1.055f), (0.055f / 1.055f), 0.f, 0.04045f, (1.f / 12.92f), 0.f};
+        case k2Dot2Curve_SkGammaNamed:
+            return value_to_parametric(2.2f);
+        default:
+            SkASSERT(false);
+            return {-1.f, -1.f, -1.f, -1.f, -1.f, -1.f, -1.f};
+    }
+}
+
+static inline SkColorSpaceTransferFn gamma_to_parametric(const SkGammas& gammas, int channel) {
+    switch (gammas.type(channel)) {
+        case SkGammas::Type::kNamed_Type:
+            return gammanamed_to_parametric(gammas.data(channel).fNamed);
+        case SkGammas::Type::kValue_Type:
+            return value_to_parametric(gammas.data(channel).fValue);
+        case SkGammas::Type::kParam_Type:
+            return gammas.params(channel);
+        default:
+            SkASSERT(false);
+            return {-1.f, -1.f, -1.f, -1.f, -1.f, -1.f, -1.f};
+    }
+}
+static inline SkColorSpaceTransferFn invert_parametric(const SkColorSpaceTransferFn& fn) {
+    // Original equation is:       y = (ax + b)^g + c   for x >= d
+    //                             y = ex + f           otherwise
+    //
+    // so 1st inverse is:          (y - c)^(1/g) = ax + b
+    //                             x = ((y - c)^(1/g) - b) / a
+    //
+    // which can be re-written as: x = (1/a)(y - c)^(1/g) - b/a
+    //                             x = ((1/a)^g)^(1/g) * (y - c)^(1/g) - b/a
+    //                             x = ([(1/a)^g]y + [-((1/a)^g)c]) ^ [1/g] + [-b/a]
+    //
+    // and 2nd inverse is:         x = (y - f) / e
+    // which can be re-written as: x = [1/e]y + [-f/e]
+    //
+    // and now both can be expressed in terms of the same parametric form as the
+    // original - parameters are enclosed in square barckets.
+
+    // find inverse for linear segment (if possible)
+    float e, f;
+    if (0.f == fn.fE) {
+        // otherwise assume it should be 0 as it is the lower segment
+        // as y = f is a constant function
+        e = 0.f;
+        f = 0.f;
+    } else {
+        e = 1.f / fn.fE;
+        f = -fn.fF / fn.fE;
+    }
+    // find inverse for the other segment (if possible)
+    float g, a, b, c;
+    if (0.f == fn.fA || 0.f == fn.fG) {
+        // otherwise assume it should be 1 as it is the top segment
+        // as you can't invert the constant functions y = b^g + c, or y = 1 + c
+        g = 1.f;
+        a = 0.f;
+        b = 0.f;
+        c = 1.f;
+    } else {
+        g = 1.f / fn.fG;
+        a = powf(1.f / fn.fA, fn.fG);
+        b = -a * fn.fC;
+        c = -fn.fB / fn.fA;
+    }
+    const float d = fn.fE * fn.fD + fn.fF;
+    return {g, a, b, c, d, e, f};
+}
+
+SkColorSpaceXform_A2B::SkColorSpaceXform_A2B(SkColorSpace_A2B* srcSpace,
+                                             SkColorSpace_XYZ* dstSpace)
+    : fLinearDstGamma(kLinear_SkGammaNamed == dstSpace->gammaNamed()) {
+#if (SkCSXformPrintfDefined)
+    static const char* debugGammaNamed[4] = {
+        "Linear", "SRGB", "2.2", "NonStandard"
+    };
+    static const char* debugGammas[5] = {
+        "None", "Named", "Value", "Table", "Param"
+    };
+#endif
+    // add in all device -> PCS xforms

[msarett1, 2016/11/11 14:36:51]

nit: Maybe "device" isn't the right word here?  Could say "encoded" or just
"xforms to PCS"

[raftias, 2016/11/11 19:36:05]

Acknowledged.

+    for (int i = 0; i < srcSpace->count(); ++i) {
+        const SkColorSpace_A2B::Element& e = srcSpace->element(i);
+        switch (e.type()) {
+            case SkColorSpace_A2B::Element::Type::kGammaNamed:
+                if (kLinear_SkGammaNamed != e.gammaNamed()) {
+                    SkCSXformPrintf("Gamma stage added: %s\n",
+                                    debugGammaNamed[(int)e.gammaNamed()]);
+                    addGamma(ApplyParametric(gammanamed_to_parametric(e.gammaNamed())),
+                             kRGB_Channels);
+                }
+                break;
+            case SkColorSpace_A2B::Element::Type::kGammas: {
+                    const SkGammas& gammas = e.gammas();
+                    SkCSXformPrintf("Gamma stage added:");
+                    for (int channel = 0; channel < 3; ++channel) {
+                        SkCSXformPrintf("  %s", debugGammas[(int)gammas.type(channel)]);
+                    }
+                    SkCSXformPrintf("\n");
+                    bool gammaNeedsRef = false;
+                    for (int channel = 0; channel < 3; ++channel) {
+                        if (SkGammas::Type::kTable_Type == gammas.type(channel)) {
+                            addGamma(ApplyTable(gammas.table(channel),
+                                                gammas.data(channel).fTable.fSize),
+                                                static_cast<Channels>(channel));
+                            gammaNeedsRef = true;
+                        } else {
+                            addGamma(ApplyParametric(gamma_to_parametric(gammas, channel)),
+                                     static_cast<Channels>(channel));
+                        }
+                    }
+                    if (gammaNeedsRef) {
+                        fGammaRefs.push_back(sk_ref_sp(&gammas));
+                    }
+                }
+                break;
+            case SkColorSpace_A2B::Element::Type::kCLUT:
+                SkCSXformPrintf("CLUT stage added [%d][%d][%d]\n", e.colorLUT().fGridPoints[0],
+                                e.colorLUT().fGridPoints[1], e.colorLUT().fGridPoints[2]);
+                fCLUTs.push_back(sk_ref_sp(&e.colorLUT()));
+                fElementsPipeline.append(SkRasterPipeline::color_lookup_table,
+                                         fCLUTs.back().get());
+                break;
+            case SkColorSpace_A2B::Element::Type::kMatrix:
+                if (!e.matrix().isIdentity()) {
+                    SkCSXformPrintf("Matrix stage added\n");
+                    addMatrix(e.matrix());
+                }
+                break;
+        }
+    }
+
+    // Lab PCS -> XYZ PCS
+    if (SkColorSpace_A2B::PCS::kLAB == srcSpace->pcs()) {
+        SkCSXformPrintf("Lab -> XYZ element added\n");
+        fElementsPipeline.append(SkRasterPipeline::lab_to_xyz);
+    }
+
+    // and XYZ PCS -> device xforms
+    if (!dstSpace->fromXYZD50()->isIdentity()) {
+        addMatrix(*dstSpace->fromXYZD50());
+    }
+
+    if (kNonStandard_SkGammaNamed != dstSpace->gammaNamed()) {
+        if (!fLinearDstGamma) {
+            addGamma(ApplyParametric(

[msarett1, 2016/11/11 14:36:51]

nit: Can this somehow fit on two lines?

[raftias, 2016/11/11 19:36:05]

Not without making kRGB_Channels look like an argument to ApplyParametric()
instead of addGamma()

+                            invert_parametric(gammanamed_to_parametric(dstSpace->gammaNamed()))),
+                     kRGB_Channels);
+        }
+    } else {
+        for (int channel = 0; channel < 3; ++channel) {
+            const SkGammas& gammas = *dstSpace->gammas();
+            if (SkGammas::Type::kTable_Type == gammas.type(channel)) {

[msarett1, 2016/11/11 14:36:51]

nit: Can you make the code in this if statement a call to a static helper
function (that builds the inverse table)?

[raftias, 2016/11/11 19:36:05]

Done.

+                constexpr int kInvTableSize = 256;
+                fGammaTables.push_front(std::vector<float>(kInvTableSize));
+                float* dstTable = fGammaTables.front().data();
+                for (int i = 0; i < kInvTableSize; ++i) {
+                    const float x = ((float) i) * (1.0f / ((float) (kInvTableSize - 1)));
+                    const float y = inverse_interp_lut(x, gammas.table(channel),
+                                                       gammas.data(channel).fTable.fSize);
+                    dstTable[i] = y;
+                }
+                addGamma(ApplyTable(dstTable, fGammaTables.front().size()),
+                         static_cast<Channels>(channel));
+            } else {
+                addGamma(ApplyParametric(invert_parametric(gamma_to_parametric(gammas, channel))),
+                         static_cast<Channels>(channel));
+            }
+        }
+    }
+}
+
+void SkColorSpaceXform_A2B::addGamma(std::function<float(float)> fn, Channels channels) {
+    fGammaFunctions.push_front(std::move(fn));
+    switch (channels) {
+        case kRGB_Channels:
+            fElementsPipeline.append(SkRasterPipeline::fn_1_r, &fGammaFunctions.front());
+            fElementsPipeline.append(SkRasterPipeline::fn_1_g, &fGammaFunctions.front());
+            fElementsPipeline.append(SkRasterPipeline::fn_1_b, &fGammaFunctions.front());
+            break;
+        case kR_Channels:
+            fElementsPipeline.append(SkRasterPipeline::fn_1_r, &fGammaFunctions.front());
+            break;
+        case kG_Channels:
+            fElementsPipeline.append(SkRasterPipeline::fn_1_g, &fGammaFunctions.front());
+            break;
+        case kB_Channels:
+            fElementsPipeline.append(SkRasterPipeline::fn_1_b, &fGammaFunctions.front());
+            break;
+        default:
+            SkASSERT(false);
+    }
+}
+
+void SkColorSpaceXform_A2B::addMatrix(const SkMatrix44& matrix) {
+    fMatrices.push_front(std::vector<float>(12));
+    auto& m = fMatrices.front();
+    m[ 0] = matrix.get(0, 0);
+    m[ 1] = matrix.get(1, 0);
+    m[ 2] = matrix.get(2, 0);
+    m[ 3] = matrix.get(0, 1);
+    m[ 4] = matrix.get(1, 1);
+    m[ 5] = matrix.get(2, 1);
+    m[ 6] = matrix.get(0, 2);
+    m[ 7] = matrix.get(1, 2);
+    m[ 8] = matrix.get(2, 2);
+    m[ 9] = matrix.get(0, 3);
+    m[10] = matrix.get(1, 3);
+    m[11] = matrix.get(2, 3);
+    SkASSERT(matrix.get(3, 0) == 0.f);
+    SkASSERT(matrix.get(3, 1) == 0.f);
+    SkASSERT(matrix.get(3, 2) == 0.f);
+    SkASSERT(matrix.get(3, 3) == 1.f);
+    fElementsPipeline.append(SkRasterPipeline::matrix_3x4, m.data());
+    fElementsPipeline.append(SkRasterPipeline::clamp_0);
+    fElementsPipeline.append(SkRasterPipeline::clamp_a);
+}