Create SkColorSpaceXform to handle color conversions

src/core/SkColorSpaceXform.cpp

+/*
+ * 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 "SkColorPriv.h"
+#include "SkColorSpace_Base.h"
+#include "SkColorSpaceXform.h"
+
+bool compute_gamut_xform(SkMatrix44* srcToDst, const SkMatrix44& srcToXYZ,
+                         const SkMatrix44& dstToXYZ) {
+    if (!dstToXYZ.invert(srcToDst)) {
+        return false;
+    }
+
+    srcToDst->postConcat(srcToXYZ);
+    return true;
+}
+
+std::unique_ptr<SkColorSpaceXform> SkColorSpaceXform::New(const sk_sp<SkColorSpace>& srcSpace,
+                                                          const sk_sp<SkColorSpace>& dstSpace) {
+    if (!srcSpace || !dstSpace) {
+        return nullptr;
+    }
+
+    if (as_CSB(srcSpace)->gammas()->isValues() && as_CSB(dstSpace)->gammas()->isValues()) {
+        SkMatrix44 srcToDst(SkMatrix44::kUninitialized_Constructor);
+        if (!compute_gamut_xform(&srcToDst, srcSpace->xyz(), dstSpace->xyz())) {
+            return nullptr;
+        }
+
+        float srcGammas[3];
+        float dstGammas[3];
+        srcGammas[0] = as_CSB(srcSpace)->gammas()->fRed.fValue;
+        srcGammas[1] = as_CSB(srcSpace)->gammas()->fGreen.fValue;
+        srcGammas[2] = as_CSB(srcSpace)->gammas()->fBlue.fValue;
+        dstGammas[0] = 1.0f / as_CSB(dstSpace)->gammas()->fRed.fValue;
+        dstGammas[1] = 1.0f / as_CSB(dstSpace)->gammas()->fGreen.fValue;
+        dstGammas[2] = 1.0f / as_CSB(dstSpace)->gammas()->fBlue.fValue;
+
+        return std::unique_ptr<SkColorSpaceXform>(
+                new SkGammaByValueXform(srcGammas, srcToDst, dstGammas));
+    }
+
+    // Unimplemeted
+    return nullptr;
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+SkGammaByValueXform::SkGammaByValueXform(float srcGammas[3], const SkMatrix44& srcToDst,
+                                         float dstGammas[3])
+    : fSrcToDst(srcToDst)
+{
+    memcpy(fSrcGammas, srcGammas, 3 * sizeof(float));
+    memcpy(fDstGammas, dstGammas, 3 * sizeof(float));
+}
+
+static uint8_t clamp_float_to_byte(float v) {
+    v = v * 255.0f;
+    if (v > 255.0f) {
+        return 255;
+    } else if (v <= 0.0f) {
+        return 0;
+    } else {
+        return (uint8_t) (v + 0.5f);
+    }
+}
+
+void SkGammaByValueXform::xform_RGBA_8888(uint32_t* dst, const uint32_t* src, uint32_t len) const {
+    while (len-- > 0) {
+        float srcFloats[3];
+        srcFloats[0] = ((*src >>  0) & 0xFF) * (1.0f / 255.0f);
+        srcFloats[1] = ((*src >>  8) & 0xFF) * (1.0f / 255.0f);
+        srcFloats[2] = ((*src >> 16) & 0xFF) * (1.0f / 255.0f);
+
+        // Convert to linear.
+        srcFloats[0] = pow(srcFloats[0], fSrcGammas[0]);
+        srcFloats[1] = pow(srcFloats[1], fSrcGammas[1]);
+        srcFloats[2] = pow(srcFloats[2], fSrcGammas[2]);
+
+        // Convert to dst gamut.
+        float dstFloats[3];
+        dstFloats[0] = srcFloats[0] * fSrcToDst.getFloat(0, 0) +
+                       srcFloats[1] * fSrcToDst.getFloat(1, 0) +
+                       srcFloats[2] * fSrcToDst.getFloat(2, 0) + fSrcToDst.getFloat(3, 0);
+        dstFloats[1] = srcFloats[0] * fSrcToDst.getFloat(0, 1) +
+                       srcFloats[1] * fSrcToDst.getFloat(1, 1) +
+                       srcFloats[2] * fSrcToDst.getFloat(2, 1) + fSrcToDst.getFloat(3, 1);
+        dstFloats[2] = srcFloats[0] * fSrcToDst.getFloat(0, 2) +
+                       srcFloats[1] * fSrcToDst.getFloat(1, 2) +
+                       srcFloats[2] * fSrcToDst.getFloat(2, 2) + fSrcToDst.getFloat(3, 2);
+
+        // Convert to dst gamma.
+        dstFloats[0] = pow(dstFloats[0], fDstGammas[0]);
+        dstFloats[1] = pow(dstFloats[1], fDstGammas[1]);
+        dstFloats[2] = pow(dstFloats[2], fDstGammas[2]);
+
+        *dst = SkPackARGB32NoCheck(((*src >> 24) & 0xFF),
+                                   clamp_float_to_byte(dstFloats[0]),
+                                   clamp_float_to_byte(dstFloats[1]),
+                                   clamp_float_to_byte(dstFloats[2]));
+
+        dst++;
+        src++;
+    }
+}