HDR: Do nonlinear blending in the compositor

ui/gfx/color_space.h

 // Copyright (c) 2012 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.
 
 #ifndef UI_GFX_COLOR_SPACE_H_
 #define UI_GFX_COLOR_SPACE_H_
 
 #include <stdint.h>
 
 #include "base/gtest_prod_util.h"
@@ skipping 45 matching lines @@
     LINEAR,
     LOG,
     LOG_SQRT,
     IEC61966_2_4,
     BT1361_ECG,
     IEC61966_2_1,
     BT2020_10,
     BT2020_12,
     SMPTEST2084,
     SMPTEST428_1,
-    ARIB_STD_B67,  // // AKA hybrid-log gamma, HLG.
+    ARIB_STD_B67,  // AKA hybrid-log gamma, HLG.
     // This is an ad-hoc transfer function that decodes SMPTE 2084 content
-    // into a 0-1 range more or less suitable for viewing on a non-hdr
+    // into a [0, 1] range more or less suitable for viewing on a non-hdr
     // display.
     SMPTEST2084_NON_HDR,
-    // Like LINEAR, but intended for HDR. (can go outside of 0-1)
+    // The same as IEC61966_2_1 on the interval [0, 1], with the nonlinear
+    // segment continuing beyond 1 and point symmetry defining values below 0.
+    IEC61966_2_1_HDR,
+    // The same as LINEAR but is defined for all real values.
     LINEAR_HDR,
     CUSTOM,
     LAST = CUSTOM,
   };
 
   enum class MatrixID : int16_t {
     INVALID,
     RGB,
     BT709,
     FCC,
@@ skipping 35 matching lines @@
                                 int h264_transfer,
                                 int h264_matrix,
                                 RangeID range_id);
 
   // Returns true if this is not the default-constructor object.
   bool IsValid() const;
 
   static ColorSpace CreateSRGB();
   static ColorSpace CreateCustom(const SkMatrix44& to_XYZD50,
                                  const SkColorSpaceTransferFn& fn);
-  // scRGB is like RGB, but linear and values outside of 0-1 are allowed.
-  // scRGB is normally used with fp16 textures.
+  static ColorSpace CreateXYZD50();
+
+  // Extended sRGB matches sRGB for values in [0, 1], and extends the transfer
+  // function to all real values.
+  static ColorSpace CreateExtendedSRGB();
+  // scRGB uses the same primaries as sRGB but has a linear transfer function
+  // for all real values.
   static ColorSpace CreateSCRGBLinear();
-  static ColorSpace CreateXYZD50();
 
   // TODO: Remove these, and replace with more generic constructors.
   static ColorSpace CreateJpeg();
   static ColorSpace CreateREC601();
   static ColorSpace CreateREC709();
 
   bool operator==(const ColorSpace& other) const;
   bool operator!=(const ColorSpace& other) const;
   bool operator<(const ColorSpace& other) const;
 
@@ skipping 17 matching lines @@
 
   void GetPrimaryMatrix(SkMatrix44* to_XYZD50) const;
   bool GetTransferFunction(SkColorSpaceTransferFn* fn) const;
   bool GetInverseTransferFunction(SkColorSpaceTransferFn* fn) const;
 
   // For most formats, this is the RGB to YUV matrix.
   void GetTransferMatrix(SkMatrix44* matrix) const;
   void GetRangeAdjustMatrix(SkMatrix44* matrix) const;
 
  private:
+  // Returns true if the transfer function is defined by an
+  // SkColorSpaceTransferFn which is extended to all real values.
+  bool HasExtendedSkTransferFn() const;
+
   PrimaryID primaries_ = PrimaryID::INVALID;
   TransferID transfer_ = TransferID::INVALID;
   MatrixID matrix_ = MatrixID::INVALID;
   RangeID range_ = RangeID::INVALID;
 
   // Only used if primaries_ is PrimaryID::CUSTOM.
   float custom_primary_matrix_[9] = {0, 0, 0, 0, 0, 0, 0, 0};
 
   // Only used if transfer_ is TransferID::CUSTOM. This array consists of the A
   // through G entries of the SkColorSpaceTransferFn structure in alphabetical
   // order.
   float custom_transfer_params_[7] = {0, 0, 0, 0, 0, 0, 0};
 
   // This is used to look up the ICCProfile from which this ColorSpace was
   // created, if possible.
   uint64_t icc_profile_id_ = 0;
   sk_sp<SkColorSpace> icc_profile_sk_color_space_;
 
   friend class ICCProfile;
   friend class ColorTransform;
   friend class ColorTransformInternal;
   friend class ColorSpaceWin;
   friend struct IPC::ParamTraits<gfx::ColorSpace>;
   FRIEND_TEST_ALL_PREFIXES(SimpleColorSpace, GetColorSpace);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_COLOR_SPACE_H_