Add SkDefaultXform as a catch-all to handle color conversions

tests/ColorSpaceXformTest.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 "Resources.h"
+#include "SkCodec.h"
+#include "SkColorPriv.h"
+#include "SkColorSpace.h"
+#include "SkColorSpace_Base.h"
+#include "SkColorSpaceXform.h"
+#include "Test.h"
+
+class ColorSpaceXformTest {
+public:
+    static SkDefaultXform* CreateDefaultXform(const sk_sp<SkGammas>& srcGamma,
+            const SkMatrix44& srcToDst, const sk_sp<SkGammas>& dstGamma) {
+        return new SkDefaultXform(srcGamma, srcToDst, dstGamma);
+    }
+};
+
+static void test_xform(skiatest::Reporter* r, const sk_sp<SkGammas>& gammas) {
+    // Arbitrary set of 10 pixels
+    constexpr int width = 10;
+    const uint32_t srcPixels[width] = {

[scroggo, 2016/06/06 14:06:45]

can this be constexpr too?

[msarett, 2016/06/06 17:33:44]

Yes I think so.

+            0xFFABCDEF, 0xFF146829, 0xFF382759, 0xFF184968, 0xFFDE8271,
+            0xFF32AB52, 0xFF0383BC, 0xFF000000, 0xFFFFFFFF, 0xFFDDEEFF, };
+    uint32_t dstPixels[width];
+
+    // Identity matrix
+    SkMatrix44 srcToDst = SkMatrix44::I();
+
+    // Create and perform xform
+    std::unique_ptr<SkColorSpaceXform> xform(
+            ColorSpaceXformTest::CreateDefaultXform(gammas, srcToDst, gammas));
+    xform->xform_RGBA_8888(dstPixels, srcPixels, width);
+
+    // Since the matrix is the identity, and the gamma curves match, the pixels
+    // should be unchanged.
+    for (int i = 0; i < width; i++) {
+        // TODO (msarett):
+        // As the implementation changes, we may want to use a tolerance here.
+        REPORTER_ASSERT(r, ((srcPixels[i] >>  0) & 0xFF) == SkGetPackedR32(dstPixels[i]));
+        REPORTER_ASSERT(r, ((srcPixels[i] >>  8) & 0xFF) == SkGetPackedG32(dstPixels[i]));
+        REPORTER_ASSERT(r, ((srcPixels[i] >> 16) & 0xFF) == SkGetPackedB32(dstPixels[i]));
+        REPORTER_ASSERT(r, ((srcPixels[i] >> 24) & 0xFF) == SkGetPackedA32(dstPixels[i]));
+    }
+}
+
+DEF_TEST(ColorSpaceXform_Gamma, r) {
+    // Lookup-table based gamma curves
+    SkGammaCurve r0, g0, b0;
+    constexpr size_t tableSize = 10;
+    r0.fTable = std::unique_ptr<float[]>(new float[tableSize]);
+    g0.fTable = std::unique_ptr<float[]>(new float[tableSize]);
+    b0.fTable = std::unique_ptr<float[]>(new float[tableSize]);
+    r0.fTableSize = g0.fTableSize = b0.fTableSize = 10;
+    r0.fTable[0] = g0.fTable[0] = b0.fTable[0] = 0.00f;
+    r0.fTable[1] = g0.fTable[1] = b0.fTable[1] = 0.05f;
+    r0.fTable[2] = g0.fTable[2] = b0.fTable[2] = 0.10f;
+    r0.fTable[3] = g0.fTable[3] = b0.fTable[3] = 0.15f;
+    r0.fTable[4] = g0.fTable[4] = b0.fTable[4] = 0.25f;
+    r0.fTable[5] = g0.fTable[5] = b0.fTable[5] = 0.35f;
+    r0.fTable[6] = g0.fTable[6] = b0.fTable[6] = 0.45f;
+    r0.fTable[7] = g0.fTable[7] = b0.fTable[7] = 0.60f;
+    r0.fTable[8] = g0.fTable[8] = b0.fTable[8] = 0.75f;
+    r0.fTable[9] = g0.fTable[9] = b0.fTable[9] = 1.00f;
+    sk_sp<SkGammas> gammas = sk_make_sp<SkGammas>(std::move(r0), std::move(g0), std::move(b0));
+    test_xform(r, gammas);
+
+    // Parametric gamma curves

[scroggo, 2016/06/06 14:06:45]

Since this appears to be a whole new test that doesn't reuse anything, it might
be clearer to make a new DEF_TEST here.

[msarett, 2016/06/06 17:33:44]

SGTM

+    SkGammaCurve r1, g1, b1;
+
+    // Interval, switch xforms at 0.5f
+    r1.fD = g1.fD = b1.fD = 0.5f;
+
+    // First equation, Y = 0.5f * X
+    r1.fE = g1.fE = b1.fE = 0.5f;
+
+    // Second equation, Y = ((1.0f * X) + 0.0f) ^ 3.0f + 0.125f
+    // Note that the function is continuous:
+    // 0.5f * 0.5f = ((1.0f * 0.5f) + 0.0f) ^ 3.0f + 0.125f = 0.25f
+    r1.fA = g1.fA = b1.fA = 1.0f;
+    r1.fB = g1.fB = b1.fB = 0.0f;
+    r1.fC = g1.fC = b1.fC = 0.125f;
+    r1.fG = g1.fG = b1.fG = 3.0f;
+    gammas = sk_make_sp<SkGammas>(std::move(r1), std::move(g1), std::move(b1));
+    test_xform(r, gammas);
+
+
+    // Exponential gamma curves

[scroggo, 2016/06/06 14:06:45]

Again, this could probably be a new DEF_TEST.

[msarett, 2016/06/06 17:33:44]

SGTM

+    SkGammaCurve r2, g2, b2;
+    r2.fValue = g2.fValue = b2.fValue = 4.0f;
+    gammas = sk_make_sp<SkGammas>(std::move(r2), std::move(g2), std::move(b2));
+    test_xform(r, gammas);
+}