color: Clarify default behaviors

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 10 matching lines @@
 namespace gfx {
 
 class ICCProfile;
 
 // Used to represet a color space for the purpose of color conversion.
 // This is designed to be safe and compact enough to send over IPC
 // between any processes.
 class GFX_EXPORT ColorSpace {
  public:
   enum class PrimaryID : uint16_t {
-    // The first 0-255 values should match the H264 specification (see Table E-3
-    // Colour Primaries in https://www.itu.int/rec/T-REC-H.264/en).
-    RESERVED0 = 0,
-    BT709 = 1,
-    UNSPECIFIED = 2,
-    RESERVED = 3,
-    BT470M = 4,
-    BT470BG = 5,
-    SMPTE170M = 6,
-    SMPTE240M = 7,
-    FILM = 8,
-    BT2020 = 9,
-    SMPTEST428_1 = 10,
-    SMPTEST431_2 = 11,
-    SMPTEST432_1 = 12,
+    RESERVED0 = 1000,
+    FIRST_VIDEO_VALUE = RESERVED0,
+    BT709 = 1001,
+    UNSPECIFIED = 1002,
+    RESERVED = 1003,
+    BT470M = 1004,
+    BT470BG = 1005,
+    SMPTE170M = 1006,
+    SMPTE240M = 1007,
+    FILM = 1008,
+    BT2020 = 1009,
+    SMPTEST428_1 = 1010,
+    SMPTEST431_2 = 1011,
+    SMPTEST432_1 = 1012,
+    LAST_VIDEO_VALUE = SMPTEST432_1,
 
-    LAST_STANDARD_VALUE = SMPTEST432_1,
-
-    // Chrome-specific values start at 1000.
-    UNKNOWN = 1000,
     XYZ_D50,
     ADOBE_RGB,
     CUSTOM,
-    LAST = CUSTOM
+    INVALID,
+    LAST = INVALID
   };
 
   enum class TransferID : uint16_t {
-    // The first 0-255 values should match the H264 specification (see Table E-4
-    // Transfer Characteristics in https://www.itu.int/rec/T-REC-H.264/en).
-    RESERVED0 = 0,
-    BT709 = 1,
-    UNSPECIFIED = 2,
-    RESERVED = 3,
-    GAMMA22 = 4,
-    GAMMA28 = 5,
-    SMPTE170M = 6,
-    SMPTE240M = 7,
-    LINEAR = 8,
-    LOG = 9,
-    LOG_SQRT = 10,
-    IEC61966_2_4 = 11,
-    BT1361_ECG = 12,
-    IEC61966_2_1 = 13,
-    BT2020_10 = 14,
-    BT2020_12 = 15,
-    SMPTEST2084 = 16,
-    SMPTEST428_1 = 17,
-    ARIB_STD_B67 = 18,  // AKA hybrid-log gamma, HLG.
+    RESERVED0 = 1000,

[hubbe, 2017/02/16 05:02:39]

Actually, this is really weird to me.
Either we embrace that the values are EXACTLY THE SAME, or we do not.
If we do not, then having numbered values is just silly.

+    FIRST_VIDEO_VALUE = RESERVED0,
+    BT709 = 1001,
+    UNSPECIFIED = 1002,
+    RESERVED = 1003,
+    GAMMA22 = 1004,
+    GAMMA28 = 1005,
+    SMPTE170M = 1006,
+    SMPTE240M = 1007,
+    LINEAR = 1008,
+    LOG = 1009,
+    LOG_SQRT = 1010,
+    IEC61966_2_4 = 1011,
+    BT1361_ECG = 1012,
+    IEC61966_2_1 = 1013,
+    BT2020_10 = 1014,
+    BT2020_12 = 1015,
+    SMPTEST2084 = 1016,
+    SMPTEST428_1 = 1017,
+    ARIB_STD_B67 = 1018,  // AKA hybrid-log gamma, HLG.
+    LAST_VIDEO_VALUE = ARIB_STD_B67,
 
-    LAST_STANDARD_VALUE = SMPTEST428_1,
-
-    // Chrome-specific values start at 1000.
-    UNKNOWN = 1000,
     GAMMA24,
 
     // 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
     // display.
     SMPTEST2084_NON_HDR,
 
     // Like LINEAR, but intended for HDR. (can go outside of 0-1)
     LINEAR_HDR,
-    // TODO(hubbe): Need to store an approximation of the gamma function(s).
     CUSTOM,
-    LAST = CUSTOM,
+    INVALID,
+    LAST = INVALID,
   };
 
   enum class MatrixID : int16_t {
-    // The first 0-255 values should match the H264 specification (see Table E-5
-    // Matrix Coefficients in https://www.itu.int/rec/T-REC-H.264/en).
-    RGB = 0,
-    BT709 = 1,
-    UNSPECIFIED = 2,
-    RESERVED = 3,
-    FCC = 4,
-    BT470BG = 5,
-    SMPTE170M = 6,
-    SMPTE240M = 7,
-    YCOCG = 8,
-    BT2020_NCL = 9,
-    BT2020_CL = 10,
-    YDZDX = 11,
-
-    LAST_STANDARD_VALUE = YDZDX,
-
-    // Chrome-specific values start at 1000
-    UNKNOWN = 1000,
-    LAST = UNKNOWN,
+    RGB = 1000,
+    FIRST_VIDEO_VALUE = RGB,
+    BT709 = 1001,
+    UNSPECIFIED = 1002,
+    RESERVED = 1003,
+    FCC = 1004,
+    BT470BG = 1005,
+    SMPTE170M = 1006,
+    SMPTE240M = 1007,
+    YCOCG = 1008,
+    BT2020_NCL = 1009,
+    BT2020_CL = 1010,
+    YDZDX = 1011,
+    LAST_VIDEO_VALUE = YDZDX,
+    INVALID,
+    LAST = INVALID,
   };
 
-  // This corresponds to the WebM Range enum which is part of WebM color data
-  // (see http://www.webmproject.org/docs/container/#Range).
-  // H.264 only uses a bool, which corresponds to the LIMITED/FULL values.
-  // Chrome-specific values start at 1000.
   enum class RangeID : int8_t {
     // Range is not explicitly specified / unknown.
     UNSPECIFIED = 0,
 
     // Limited Rec. 709 color range with RGB values ranging from 16 to 235.
     LIMITED = 1,
 
     // Full RGB color range with RGB valees from 0 to 255.
     FULL = 2,
 
     // Range is defined by TransferID/MatrixID.
     DERIVED = 3,
 
-    LAST = DERIVED
+    INVALID,
+    LAST = INVALID
   };
 
   ColorSpace();
   ColorSpace(PrimaryID primaries, TransferID transfer);
   ColorSpace(PrimaryID primaries,
              TransferID transfer,
              MatrixID matrix,
              RangeID full_range);
   ColorSpace(const ColorSpace& other);
-  ColorSpace(int primaries, int transfer, int matrix, RangeID full_range);
   ~ColorSpace();
 
-  static PrimaryID PrimaryIDFromInt(int primary_id);
-  static TransferID TransferIDFromInt(int transfer_id);
-  static MatrixID MatrixIDFromInt(int matrix_id);
+  // Create a color space with primary, transfer and matrix values from the
+  // H264 specification (Table E-3 Colour Primaries, E-4 Transfer
+  // Characteristics, and E-5 Matrix Coefficients in
+  // https://www.itu.int/rec/T-REC-H.264/en).
+  static ColorSpace CreateVideo(int h264_primary,
+                                int h264_transfer,
+                                int h264_matrix,
+                                RangeID range_id);
+  // Retrieve the H264 parameters.
+  void GetVideoParameters(int* h264_primary,

[hubbe, 2017/02/16 05:02:39]

I'd rather have four individual accessors.

+                          int* h264_transfer,
+                          int* h264_matrix,
+                          bool* full_range);
 
   // 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 CreateSCRGBLinear();
@@ skipping 16 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:
-  PrimaryID primaries_ = PrimaryID::UNSPECIFIED;
-  TransferID transfer_ = TransferID::UNSPECIFIED;
-  MatrixID matrix_ = MatrixID::UNSPECIFIED;
-  RangeID range_ = RangeID::LIMITED;
+  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_