First cut at making HDR content viewable on SDR display with color management.

ui/gfx/color_transform.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 "ui/gfx/color_transform.h"
 
 #include <vector>
 
 #include "base/logging.h"
 #include "ui/gfx/color_space.h"
@@ skipping 380 matching lines @@
           1.0f / m1);
     }
 
     case ColorSpace::TransferID::SMPTEST428_1:
       return (powf(v, 2.6f) - 52.37f) / 48.0f;
 
     // Chrome-specific values below
     case ColorSpace::TransferID::GAMMA24:
       v = fmax(0.0f, v);
       return powf(v, 2.4f);
+
+    case ColorSpace::TransferID::SMPTEST2084_NON_HDR:
+      v = fmax(0.0f, v);
+      return fmin(2.3f * pow(v, 2.8f), v / 5.0f + 0.8f);
   }
 }
 
+namespace {
+// Assumes bt2020
+float Luma(const ColorTransform::TriStim& c) {
+  return c.x() * 0.2627f + c.y() * 0.6780f + c.z() * 0.0593f;
+}
+};
+
+GFX_EXPORT ColorTransform::TriStim ToLinear(ColorSpace::TransferID id,
+                                            ColorTransform::TriStim color) {
+  ColorTransform::TriStim ret(ToLinear(id, color.x()), ToLinear(id, color.y()),
+                              ToLinear(id, color.z()));
+
+  if (id == ColorSpace::TransferID::SMPTEST2084_NON_HDR) {
+    if (Luma(ret) > 0.0) {
+      ColorTransform::TriStim smpte2084(
+          ToLinear(ColorSpace::TransferID::SMPTEST2084, color.x()),
+          ToLinear(ColorSpace::TransferID::SMPTEST2084, color.y()),
+          ToLinear(ColorSpace::TransferID::SMPTEST2084, color.z()));
+      smpte2084.Scale(Luma(ret) / Luma(smpte2084));
+      ret = smpte2084;
+    }
+  }
+
+  return ret;
+}
+
 GFX_EXPORT Transform GetTransferMatrix(ColorSpace::MatrixID id) {
   float Kr = 0.0f, Kb = 0.0f;
   switch (id) {
     case ColorSpace::MatrixID::RGB:
       return Transform();
 
     case ColorSpace::MatrixID::BT709:
     case ColorSpace::MatrixID::UNSPECIFIED:
     case ColorSpace::MatrixID::RESERVED:
       Kr = 0.2126f;
@@ skipping 88 matching lines @@
       : from_(from), to_(to) {
     if (intent == Intent::INTENT_PERCEPTUAL) {
       switch (from_.transfer_) {
         case ColorSpace::TransferID::UNSPECIFIED:
         case ColorSpace::TransferID::BT709:
         case ColorSpace::TransferID::SMPTE170M:
           // See SMPTE 1886
           from_.transfer_ = ColorSpace::TransferID::GAMMA24;
           break;
 
+        case ColorSpace::TransferID::SMPTEST2084:
+          // We don't have an HDR display, so replace SMPTE 2084 with something
+          // that returns ranges more or less suitable for a normal display.
+          from_.transfer_ = ColorSpace::TransferID::SMPTEST2084_NON_HDR;
+          break;
+
         default:  // Do nothing
           break;
       }
 
       // TODO(hubbe): shrink gamuts here (never stretch gamuts)
     }
 
     Transform* from_transfer_matrix =
         from_.matrix_ == ColorSpace::MatrixID::BT2020_CL ? &b_ : &a_;
     Transform* to_transfer_matrix =
@@ skipping 141 matching lines @@
           std::unique_ptr<ColorTransform>(
               new QCMSColorTransform(GetXYZD50Profile(), to_profile))));
     } else {
       return std::unique_ptr<ColorTransform>(
           new ColorSpaceToColorSpaceTransform(from, to, intent));
     }
   }
 }
 
 }  // namespace gfx