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..56d806a8e5af9ce4b57081004f31cfe0e3aefdad 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;