color: Clarify default behaviors

ui/gfx/color_space.h

Index: ui/gfx/color_space.h
diff --git a/ui/gfx/color_space.h b/ui/gfx/color_space.h
index 798b9305a19b28d5941eae06812167aa77fd23ae..c605a1aee9eff7c17f575d83392064bc594c6a8b 100644
--- a/ui/gfx/color_space.h
+++ b/ui/gfx/color_space.h
@@ -28,59 +28,52 @@ class ICCProfile;
 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,
-
-    LAST_STANDARD_VALUE = SMPTEST432_1,
-
-    // Chrome-specific values start at 1000.
-    UNKNOWN = 1000,
+    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,
+
     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.
-
-    LAST_STANDARD_VALUE = SMPTEST428_1,
-
-    // Chrome-specific values start at 1000.
-    UNKNOWN = 1000,
+    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,
+
     GAMMA24,
 
     // This is an ad-hoc transfer function that decodes SMPTE 2084 content
@@ -90,38 +83,30 @@ class GFX_EXPORT ColorSpace {
 
     // 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,
@@ -135,7 +120,8 @@ class GFX_EXPORT ColorSpace {
     // Range is defined by TransferID/MatrixID.
     DERIVED = 3,
 
-    LAST = DERIVED
+    INVALID,
+    LAST = INVALID
   };
 
   ColorSpace();
@@ -145,12 +131,21 @@ class GFX_EXPORT ColorSpace {
              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;
@@ -187,10 +182,10 @@ class GFX_EXPORT ColorSpace {
   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};