[css-color-4] Allow percent as well as float 0.0 to 1.0 in color() args

[svgeesus]

@faceless2 said

allowing a percentage as a synonym for 0..1 may be more natural, e.g. color(swopc 0 85% 70% 42%)

which is worthy of separate discussion.

[ghost]

The spec already allows this for several types: namely <rgb-component> and <alpha-value> in the rgba() function. So I think that it would be natural to define it as a <number-percentage>. The change still allows the full range of real numbers to be used, just in a different format. ie. 300% = 3 or 450% = 4.5, etc..

[svgeesus]

While allowing, say, 50% as a synonym for 0.5 seems unproblematic, doing so would impact #278 were @tabatkins argues for adding percentage units to the L* value. So 50 and 50% would be synonymous, except now the spec would need to clarify that here, 50% means 50 not 0.5.

Apart from that one issue, I don't see an issue with allowing percentage units as well as floats here. I don't want to hold up this issue for #278 so I'm going to agree with @faceless2 here and solve that other issue separately.

[svgeesus]

Existing tests need to be updated to also check the percentage values.

[svgeesus]

This change would also affect the gray() notation, which takes a number in the range [0,100] for example gray(50). If percentages were optional, the spec would need to specify that gray(50%) meant gray(50) not gray(0.5) which is very different.

[svgeesus]

With the recent resolution to 4649 adding lab to the color() function, this issue would require stating that all percentages resolve to 0.0 .. 1.0 except that for lab the first percentage resolves to 0.0 to 100.0.

[Crissov]

Why, though?

L* in Lab() has always been a percentage, it is just often written without the percent sign outside CSS. This is already noted in the spec as a result of #4477.

[svgeesus]

Because all the other percentages resolve to 0.0 to 1.0, and because this issue is as well as

[Crissov]

So does L* in lab(…) and color(lab,…). Itʼs always 100% = 1.0 = 1 within CSS; only outside CSS you would ever encounter 100.0 = 100 = 100%.

I see no WG resolution to make lab(50 …) or color(lab, 50 …) resolve to the same color as lab(0.5 …) or color(lab, 0.5 …). They might be clamped to lab(1.0 …) or lab(100% …) though.

[svgeesus]

Percentages as well as floats were added in Allow percent as well as float 0.0 to 1.0 in color() args

[svgeesus]

WPT tests for color() in progress

[svgeesus]

WPT tests for color() in progress

Tests now updated to take into account review feedback