Implement color-gamut media query

third_party/WebKit/Source/platform/graphics/ColorSpace.cpp

Index: third_party/WebKit/Source/platform/graphics/ColorSpace.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/ColorSpace.cpp b/third_party/WebKit/Source/platform/graphics/ColorSpace.cpp
index 423da80de12b5d9a46cc4f582641087b1078f5a0..4b2694c50386a996bb1960ebb4acc7fef6af1fdb 100644
--- a/third_party/WebKit/Source/platform/graphics/ColorSpace.cpp
+++ b/third_party/WebKit/Source/platform/graphics/ColorSpace.cpp
@@ -33,6 +33,8 @@
 #include "platform/graphics/ColorSpace.h"
 
 #include "platform/graphics/skia/SkiaUtils.h"
+#include "public/platform/WebScreenInfo.h"
+#include "third_party/skia/include/core/SkColorSpaceXform.h"
 #include "third_party/skia/include/effects/SkTableColorFilter.h"
 #include "wtf/MathExtras.h"
 #include <algorithm>
@@ -116,6 +118,59 @@ sk_sp<SkColorFilter> createColorSpaceFilter(ColorSpace srcColorSpace,
   return SkTableColorFilter::MakeARGB(0, lookupTable, lookupTable, lookupTable);
 }
 
+ColorSpaceGamut getColorSpaceGamut(const WebScreenInfo& screenInfo) {
+  const gfx::ICCProfile& profile = screenInfo.iccProfile;
+  if (profile == gfx::ICCProfile())
+    return ColorSpaceGamut::Unknown;
+
+  return ColorSpaceUtilities::getColorSpaceGamut(
+      profile.GetColorSpace().ToSkColorSpace().get());
+}
+
+ColorSpaceGamut getColorSpaceGamut(SkColorSpace* colorSpace) {

[Noel Gordon, 2017/01/31 02:29:57]

The color profile media spec does not say how to compute the color space gamut. 
How do we achieve compat while that is so?

+  sk_sp<SkColorSpace> scRGB(
+      SkColorSpace::MakeNamed(SkColorSpace::kSRGBLinear_Named));
+  std::unique_ptr<SkColorSpaceXform> transform(
+      SkColorSpaceXform::New(colorSpace, scRGB.get()));
+
+  if (!transform)
+    return ColorSpaceGamut::Unknown;
+
+  unsigned char in[3][4];
+  float out[3][4];
+  memset(in, 0, sizeof(in));
+  in[0][0] = 255;
+  in[1][1] = 255;
+  in[2][2] = 255;
+  in[0][3] = 255;
+  in[1][3] = 255;
+  in[2][3] = 255;
+  transform->apply(SkColorSpaceXform::kRGBA_F32_ColorFormat, out,
+                   SkColorSpaceXform::kRGBA_8888_ColorFormat, in, 3,
+                   kOpaque_SkAlphaType);
+  float score = out[0][0] * out[1][1] * out[2][2];

[Noel Gordon, 2017/01/31 02:29:57]

Aside: by the looks, this appears to compute a score from the principle diagnol
of the tristimulus matrix.   That is a poor measure of gamut area for profiles
having strong off-diagnol elements.  I expect that this score will produces
outliers, in that it will classify some wide gamut profiles as not being wide
gamut [1].

[1] And again for browser compat, this is the reason why the media color profile
spec needs to specify how to compute the gamut area.

[hubbe, 2017/01/31 04:06:20]

While I agree that this is a hacky method, I do think it is good enough to
work[1]. The matrix is in the sRGB coordinate space, so if the primaries are
more or less "red, green and blue" they will be roughly parallel with the sRGB
primaries. While other primaries are theoretically possible, we do not currently
support non-RGB colorspaces.

If we want a better method, we'll probably want to measure triangle overlap in
XYZ or CIELAB space...

[1] but not good enough to be standardized.

+
+  if (score < 0.9)
+    return ColorSpaceGamut::LessThanNTSC;
+  if (score < 0.95)
+    return ColorSpaceGamut::NTSC;  // actual score 0.912839
+  if (score < 1.1)
+    return ColorSpaceGamut::SRGB;  // actual score 1.0
+  if (score < 1.3)
+    return ColorSpaceGamut::AlmostP3;
+  if (score < 1.425)
+    return ColorSpaceGamut::P3;  // actual score 1.401899
+  if (score < 1.5)
+    return ColorSpaceGamut::AdobeRGB;  // actual score 1.458385
+  if (score < 2.0)
+    return ColorSpaceGamut::Wide;
+  if (score < 2.2)
+    return ColorSpaceGamut::BT2020;  // actual score 2.104520
+  if (score < 2.7)
+    return ColorSpaceGamut::ProPhoto;  // actual score 2.913247
+  return ColorSpaceGamut::UltraWide;
+}
+
 }  // namespace ColorSpaceUtilities
 
 }  // namespace blink