[css-color-4] Conversion of hsl(none none none) to srgb clarification.

[tiaanl]

In the tests here:

https://github.com/web-platform-tests/wpt/blob/master/css/css-color/parsing/color-computed-color-mix-function.html#L80

There is a test with color-mix(in hsl, hsl(none none none), hsl(none none none)) which should result in hsl(none none none) (and it does), but then of course will be converted to srgb for serialization. That result is color(srgb none none none), which I'm not sure how it is calculated.

Chrome passes the test, but that seems to be a bug. They never clear the none flags after conversion to srgb, so color-mix(in hsl, hsl(30deg 40% none), hsl(30deg 40% none)) would result in color(srgb 0 0 none), just because lightness was none.

I think we should change the test to color(srgb 0 0 0)?

[svgeesus]

From “Missing” Color Components and the none Keyword (my emphasis)

For handling of missing component in color interpolation, see § 12.2 Interpolating with Missing Components.

For all other purposes, a missing component behaves as a zero value, in the appropriate unit for that component: 0, 0%, or 0deg. This includes rendering the color directly, converting it to another color space, performing computations on the color component values, etc.

So yes, when the color() function is serialized is will have 0 not none.

[tiaanl]

Perfect, will update the test. Thank! 👍

[mysteryDate]

So, the key verbiage here from the spec is "converting it to another color space"? When the resulting hsl color is converted to srgb for serialization, the nones will get replaced with zeroes?

[mysteryDate]

Since RCS with hsl/hwb/legacy rgb involve color space conversion, would explicit "nones" become zeros here too? i.e.:

hsl(from blue none none none) = color(srgb 0 0 0)?

Does this look a little weird with legacy rgb?
rgb(from blue none none none) = color(srgb 0 0 0)?

And then, does this also apply to alpha?
rgb(from blue r g b / none) = color(srgb 0 0 1 / 0)?

while:
color(srgb from blue r g b / none) = color(srgb 0 0 1 / none)?