[css-color] Allow <angle> or <hue> in color()

[Crissov]

color() = color( [ <ident>? [ <number>+ | <string> ] [ / <alpha-value> ]? ]# , <color>? )

This allows either a named color or a tuple of unit-less numbers to identify or specify a color within a custom color space. Wouldnʼt it be useful to also support <percentage> (or <alpha-value> = <cmyk-component>) and <angle> (or <hue>) for custom color components since try are used in predefined color notations?

See #4477 for CIE lightness as a percentage.

[faceless2]

The values given to any ICC profile for conversion are 0 to 1. You can map percentages to this (and do, in #3450), but angles etc. would require knowledge which isn't readily available.

[Crissov]

Oops! This issue is mostly a duplicate of #3450 indeed. I shall limit its scope to polar coordinates then, i. e. allowing one <angle>.

<color-component> = <number> | <percentage>

color(
     [ <ident>? 
       [ <string>
       | [ <angle>? || <color-component>+ ]
       ] 
       [ / <color-component> ]? 
     ]#
     [, <color> ]? 
     )

or more restrictive:

color(
     [ <ident>? 
       [ <string>
       | [ <angle> || <color-component>{0,2} ] 
       | <color-component>+ 
       ] 
       [ / <color-component> ]? 
     ]#
     [, <color> ]? 
     )

with the standard transformation

<computed-color-components> 
  = <first-non-angle | 100%>
  , <second-non-angle | 0%> * cos(<specified-angle>) 
  , <second-non-angle | 0%> * sin(<specified-angle>)

[Crissov]

PS: @color-profile could get a descriptor to distinguish color space notations using names, channels (e. g. RGB and CMYK), Cartesian (e. g. Lab and Luv) or polar coordinates (i. e. anything with hue). UAs could then simply ignore uses of color() where the provided component types do not match the descriptor.

[svgeesus]

Closing because the current spec allows percent already

color() = color( [ [<ident> | <dashed-ident>]? [ <number-percentage>+ | <string> ] 
[ / <alpha-value> ]? ]# , <color>? )

none of the predefined spaces in color() use a hue or angle, and ICC profiles take parameters in the range 0.0 to 1.0, not angles, as already mentioned.

[Crissov]

I expected nothing else. Perhaps I should have rephrased the issue to: Allow polar coordinates for arbitrary color spaces.

color([ <ident>? 
        [ <string>
        | <polar>
        | <component>+ 
        ] [ / <component> ]? 
      ]#[, <color> ]?)

<polar> = <hue> || <component>{0,2}
<component> = <number> | <percentage>