color: Add analytic transfer functions in shaders

ui/gfx/color_transform_unittest.cc

Index: ui/gfx/color_transform_unittest.cc
diff --git a/ui/gfx/color_transform_unittest.cc b/ui/gfx/color_transform_unittest.cc
index 36e3ab21e958862b229fd21559793cb1c818f4f3..1ccfe753115e01e92bdcfe8585ec18cba2089695 100644
--- a/ui/gfx/color_transform_unittest.cc
+++ b/ui/gfx/color_transform_unittest.cc
@@ -82,6 +82,46 @@ TEST(SimpleColorSpace, BT709toSRGB) {
   EXPECT_GT(tmp.z(), tmp.y());
 }
 
+TEST(SimpleColorSpace, TransferFnCancel) {
+  ColorSpace::PrimaryID primary = ColorSpace::PrimaryID::BT709;
+  ColorSpace::MatrixID matrix = ColorSpace::MatrixID::RGB;
+  ColorSpace::RangeID range = ColorSpace::RangeID::FULL;
+
+  // BT709 has a gamma of 2.2222 (with some adjustments)
+  ColorSpace bt709(primary, ColorSpace::TransferID::BT709, matrix, range);
+
+  // IEC61966_2_1 has the sRGB gamma of 2.4 (with some adjustments)
+  ColorSpace srgb(primary, ColorSpace::TransferID::IEC61966_2_1, matrix, range);
+
+  // gamma28 is a simple exponential
+  ColorSpace gamma28(primary, ColorSpace::TransferID::GAMMA28, matrix, range);
+
+  // gamma24 is a simple exponential
+  ColorSpace gamma24(primary, ColorSpace::TransferID::GAMMA24, matrix, range);
+
+  // BT709 source is common for video and sRGB destination is common for
+  // monitors. The two transfer functions are very close, and should cancel
+  // out (so the transfer between them should be the identity). This particular
+  // case is important for power reasons.
+  std::unique_ptr<ColorTransform> bt709_to_srgb(
+      ColorTransform::NewColorTransform(
+          bt709, srgb, ColorTransform::Intent::INTENT_PERCEPTUAL));
+  EXPECT_EQ(bt709_to_srgb->NumberOfStepsForTesting(), 0u);
+
+  // Gamma 2.8 isn't even close to BT709 and won't cancel out (so we will have
+  // two steps in the transform -- to-linear and from-linear).
+  std::unique_ptr<ColorTransform> bt709_to_gamma28(
+      ColorTransform::NewColorTransform(
+          bt709, gamma28, ColorTransform::Intent::INTENT_PERCEPTUAL));
+  EXPECT_EQ(bt709_to_gamma28->NumberOfStepsForTesting(), 2u);
+
+  // Gamma 2.4 is closer to BT709, but not close enough to actually cancel out.
+  std::unique_ptr<ColorTransform> bt709_to_gamma24(
+      ColorTransform::NewColorTransform(
+          bt709, gamma24, ColorTransform::Intent::INTENT_PERCEPTUAL));
+  EXPECT_EQ(bt709_to_gamma24->NumberOfStepsForTesting(), 2u);
+}
+
 TEST(SimpleColorSpace, SRGBFromICCAndNotICC) {
   float kEpsilon = 0.001f;
   ColorTransform::TriStim value_fromicc;
@@ -232,6 +272,112 @@ TEST(SimpleColorSpace, DefaultToSRGB) {
   EXPECT_EQ(t2->NumberOfStepsForTesting(), 0u);
 }
 
+// This tests to make sure that we don't emit the "if" or "pow" parts of a
+// transfer function unless necessary.
+TEST(SimpleColorSpace, ShaderSourceTrFnOptimizations) {
+  SkMatrix44 primaries;
+  gfx::ColorSpace::CreateSRGB().GetPrimaryMatrix(&primaries);
+
+  SkColorSpaceTransferFn fn_no_pow_no_if = {
+      1.f, 2.f, 0.f, 1.f, 0.f, 0.f, 0.f,
+  };
+  SkColorSpaceTransferFn fn_no_pow_yes_if = {
+      1.f, 2.f, 0.f, 1.f, 0.5f, 0.f, 0.f,
+  };
+  SkColorSpaceTransferFn fn_yes_pow_no_if = {
+      2.f, 2.f, 0.f, 1.f, 0.f, 0.f, 0.f,
+  };
+  SkColorSpaceTransferFn fn_yes_pow_yes_if = {
+      2.f, 2.f, 0.f, 1.f, 0.5f, 0.f, 0.f,
+  };
+
+  gfx::ColorSpace src;
+  gfx::ColorSpace dst = gfx::ColorSpace::CreateXYZD50();
+  std::string shader_string;
+
+  src = gfx::ColorSpace::CreateCustom(primaries, fn_no_pow_no_if);
+  shader_string = ColorTransform::NewColorTransform(
+                      src, dst, ColorTransform::Intent::INTENT_PERCEPTUAL)
+                      ->GetShaderSource();
+  EXPECT_EQ(shader_string.find("if ("), std::string::npos);
+  EXPECT_EQ(shader_string.find("pow("), std::string::npos);
+
+  src = gfx::ColorSpace::CreateCustom(primaries, fn_no_pow_yes_if);
+  shader_string = ColorTransform::NewColorTransform(
+                      src, dst, ColorTransform::Intent::INTENT_PERCEPTUAL)
+                      ->GetShaderSource();
+  EXPECT_NE(shader_string.find("if ("), std::string::npos);
+  EXPECT_EQ(shader_string.find("pow("), std::string::npos);
+
+  src = gfx::ColorSpace::CreateCustom(primaries, fn_yes_pow_no_if);
+  shader_string = ColorTransform::NewColorTransform(
+                      src, dst, ColorTransform::Intent::INTENT_PERCEPTUAL)
+                      ->GetShaderSource();
+  EXPECT_EQ(shader_string.find("if ("), std::string::npos);
+  EXPECT_NE(shader_string.find("pow("), std::string::npos);
+
+  src = gfx::ColorSpace::CreateCustom(primaries, fn_yes_pow_yes_if);
+  shader_string = ColorTransform::NewColorTransform(
+                      src, dst, ColorTransform::Intent::INTENT_PERCEPTUAL)
+                      ->GetShaderSource();
+  EXPECT_NE(shader_string.find("if ("), std::string::npos);
+  EXPECT_NE(shader_string.find("pow("), std::string::npos);
+}
+
+// Note: This is not actually "testing" anything -- the goal of this test is to
+// to make reviewing shader code simpler by giving an example of the resulting
+// shader source. This should be updated whenever shader generation is updated.
+// This test produces slightly different results on Android.
+#if defined(OS_ANDROID)
+#define MAYBE_SampleShaderSource DISABLED_SampleShaderSource
+#else
+#define MAYBE_SampleShaderSource SampleShaderSource
+#endif
+TEST(SimpleColorSpace, MAYBE_SampleShaderSource) {
+  ColorSpace bt709 = ColorSpace::CreateREC709();
+  ColorSpace output(ColorSpace::PrimaryID::BT2020,
+                    ColorSpace::TransferID::GAMMA28);
+  std::string source =
+      ColorTransform::NewColorTransform(
+          bt709, output, ColorTransform::Intent::INTENT_PERCEPTUAL)
+          ->GetShaderSource();
+  std::string expected =
+      "vec3 DoColorConversion(vec3 color) {\n"
+      "  color = mat3(+1.16438353e+00, +1.16438353e+00, +1.16438353e+00,\n"
+      "               -2.28029018e-09, -2.13248596e-01, +2.11240172e+00,\n"
+      "               +1.79274118e+00, -5.32909274e-01, -5.96049432e-10)"
+      " * color;\n"
+      "  color = vec3(-9.69429970e-01, +3.00019622e-01, -1.12926030e+00)"
+      " + color;\n"
+      "  if (color.r < 0.040450)\n"
+      "    color.r = +7.73993805e-02 * color.r;\n"
+      "  else\n"
+      "    color.r = pow(+9.47867334e-01 * color.r + +5.21326549e-02, "
+      "+2.40000010e+00);\n"
+      "  if (color.g < 0.040450)\n"
+      "    color.g = +7.73993805e-02 * color.g;\n"
+      "  else\n"
+      "    color.g = pow(+9.47867334e-01 * color.g + +5.21326549e-02, "
+      "+2.40000010e+00);\n"
+      "  if (color.b < 0.040450)\n"
+      "    color.b = +7.73993805e-02 * color.b;\n"
+      "  else\n"
+      "    color.b = pow(+9.47867334e-01 * color.b + +5.21326549e-02, "
+      "+2.40000010e+00);\n"
+      "  color = mat3(+6.27403915e-01, +6.90973178e-02, +1.63914412e-02,\n"
+      "               +3.29283148e-01, +9.19540286e-01, +8.80132914e-02,\n"
+      "               +4.33131084e-02, +1.13623003e-02, +8.95595253e-01) "
+      "* color;\n"
+      "  color = vec3(+0.00000000e+00, +0.00000000e+00, +0.00000000e+00) "
+      "+ color;\n"
+      "  color.r = pow(color.r, +3.57142866e-01);\n"
+      "  color.g = pow(color.g, +3.57142866e-01);\n"
+      "  color.b = pow(color.b, +3.57142866e-01);\n"
+      "  return color;\n"
+      "}\n";
+  EXPECT_EQ(source, expected);
+}
+
 class TransferTest : public testing::TestWithParam<ColorSpace::TransferID> {};
 
 TEST_P(TransferTest, basicTest) {