color: general transformation -> affine transformation

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 3c4364bcb9b45e27bfe0826ac7db8a2a712f95d8..67183a532a429e527caee9eace11219dc491604c 100644
--- a/ui/gfx/color_transform_unittest.cc
+++ b/ui/gfx/color_transform_unittest.cc
@@ -83,6 +83,35 @@ TEST(SimpleColorSpace, BT709toSRGB) {
   EXPECT_GT(tmp.z(), tmp.y());
 }
 
+TEST(SimpleColorSpace, GetAffineApproximation) {
+  // Two linear color spaces, result should be a perfect translation.
+  ColorSpace from_colorspace(
+      ColorSpace::PrimaryID::BT709, ColorSpace::TransferID::LINEAR,
+      ColorSpace::MatrixID::BT709, ColorSpace::RangeID::FULL);
+  ColorSpace to_colorspace(
+      ColorSpace::PrimaryID::BT2020, ColorSpace::TransferID::LINEAR,
+      ColorSpace::MatrixID::RGB, ColorSpace::RangeID::FULL);
+
+  std::unique_ptr<ColorTransform> t(ColorTransform::NewColorTransform(
+      from_colorspace, to_colorspace, ColorTransform::Intent::INTENT_ABSOLUTE));
+  Transform transform;
+  EXPECT_TRUE(t->GetAffineApproximation(&transform));
+
+  for (int x = 0; x <= 2; x++) {
+    for (int y = 0; y <= 2; y++) {
+      for (int z = 0; z <= 2; z++) {
+        ColorTransform::TriStim A(x / 2.0f, y / 2.0f, z / 2.0f);
+        ColorTransform::TriStim B(A);
+        t->transform(&A, 1);
+        transform.TransformPoint(&B);
+        EXPECT_NEAR(A.x(), B.x(), 0.001);
+        EXPECT_NEAR(A.y(), B.y(), 0.001);
+        EXPECT_NEAR(A.z(), B.z(), 0.001);
+      }
+    }
+  }
+}
+
 unsigned char srgb_icc_data[] = {
     0x00, 0x00, 0x0b, 0xe8, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, 0x00,
     0x6d, 0x6e, 0x74, 0x72, 0x52, 0x47, 0x42, 0x20, 0x58, 0x59, 0x5a, 0x20,