color: Add analytic transfer functions in shaders

ui/gfx/color_transform_unittest.cc

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/logging.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/color_space.h"
 #include "ui/gfx/color_transform.h"
 #include "ui/gfx/icc_profile.h"
 #include "ui/gfx/test/icc_profiles.h"
@@ skipping 64 matching lines @@
   EXPECT_NEAR(tmp.y(), 1.0f, 0.001f);
   EXPECT_NEAR(tmp.z(), 1.0f, 0.001f);
 
   // Test a blue color
   tmp = ColorTransform::TriStim(128.0f / 255.0f, 240.0f / 255.0f, 0.5f);
   t->Transform(&tmp, 1);
   EXPECT_GT(tmp.z(), tmp.x());
   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;
   ColorTransform::TriStim value_default;
 
   ICCProfile srgb_icc_profile = ICCProfileForTestingSRGB();
   ColorSpace srgb_fromicc = srgb_icc_profile.GetColorSpace();
   ColorSpace srgb_default = gfx::ColorSpace::CreateSRGB();
   ColorSpace xyzd50 = gfx::ColorSpace::CreateXYZD50();
 
@@ skipping 238 matching lines @@
 
 INSTANTIATE_TEST_CASE_P(
     C,
     ColorSpaceTest,
     testing::Combine(testing::ValuesIn(all_primaries),
                      testing::Values(ColorSpace::TransferID::BT709),
                      testing::ValuesIn(all_matrices),
                      testing::ValuesIn(all_ranges),
                      testing::ValuesIn(intents)));
 }  // namespace