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..6e424f762a10ae8d4ce3e84e604178f4a59d3e28 100644
--- a/ui/gfx/color_space.h
+++ b/ui/gfx/color_space.h
@@ -28,26 +28,17 @@ 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,
+    INVALID,
+    BT709,
+    BT470M,
+    BT470BG,
+    SMPTE170M,
+    SMPTE240M,
+    FILM,
+    BT2020,
+    SMPTEST428_1,
+    SMPTEST431_2,
+    SMPTEST432_1,
     XYZ_D50,
     ADOBE_RGB,
     CUSTOM,
@@ -55,87 +46,58 @@ class GFX_EXPORT ColorSpace {
   };
 
   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,
+    INVALID,
+    BT709,
+    GAMMA22,
     GAMMA24,
-
+    GAMMA28,
+    SMPTE170M,
+    SMPTE240M,
+    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.
     // 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,
   };
 
   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,
+    INVALID,
+    RGB,
+    BT709,
+    FCC,
+    BT470BG,
+    SMPTE170M,
+    SMPTE240M,
+    YCOCG,
+    BT2020_NCL,
+    BT2020_CL,
+    YDZDX,
+    LAST = YDZDX,
   };
 
-  // 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,
-
+    INVALID,
     // Limited Rec. 709 color range with RGB values ranging from 16 to 235.
-    LIMITED = 1,
-
+    LIMITED,
     // Full RGB color range with RGB valees from 0 to 255.
-    FULL = 2,
-
+    FULL,
     // Range is defined by TransferID/MatrixID.
-    DERIVED = 3,
-
-    LAST = DERIVED
+    DERIVED,
+    LAST = DERIVED,
   };
 
   ColorSpace();
@@ -145,12 +107,16 @@ 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);
 
   // Returns true if this is not the default-constructor object.
   bool IsValid() const;
@@ -187,10 +153,10 @@ 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};