Percentages mishandled in color(lab L a b)

[svgeesus]

In color(lab L a b), same as lab(L a b), the L parameter is required to have a percentage and 50% resolves to an L value of 50, not 0.5.

However, color.js has two errors:

a) it allows the "%" to be omitted, for examplecolor(lab 54.903 -54.15 55.313)

b) if the percent is used, 100% resolves to an L of 1, not 100. For example color(lab 54.903% -54.15 55.313) is a near-black.

Note that lab(54.903% -54.15 55.313) is handled correctly. Although lab(54.903 -54.15 55.313) is also accepted, and treated as identical to the percentage form.

[svgeesus]

I suspect the problem is here

if (/%$/.test(arg)) {
	// Convert percentages to 0-1 numbers
	let n = new Number(+arg.slice(0, -1) / 100);
	n.percentage = true;
	return n;
}

but then that would also affect the lab() and lch() functions. Ah, they have special handling:

	let L = parsed.args[0];

	// Percentages in lab() don't translate to a 0-1 range, but a 0-100 range
	if (L.percentage) {
		parsed.args[0] = L * 100;
	}

so that same test for "is the first argument CIE L" needs to be applied to the general color() parsing in src/color.js

[svgeesus]

Confirming bug still exists

color(lab 50% 0 0) → color(lab 0.5 0 0)

[LeaVerou]

Since color(lab L a b) is not valid CSS anymore, perhaps we should just not accept it…

[svgeesus]

Agreed, provided lab(number number number) and lab(percent number number) are handled correctly with L=100% mapping to L=100 and vice-versa.

(There is also lab(percent percent percent) from CSS, but that is unrelated to this issue)

[LeaVerou]

Reopening because we do still accept it 😛 see #146

[svgeesus]

Note that lab(54.903% -54.15 55.313) is handled correctly. Although lab(54.903 -54.15 55.313) is also accepted, and treated as identical to the percentage form.

Note that CSS Color 4 has changed and using a lightness without a percent is now allowed with 0 being the same as 0% and 100 the same as 100%. So that part is now correct.

We don't accept percent for a and b though, which is also now allowed.

[svgeesus]

Ah, they have special handling:

The reference ranges for all color spaces that accept <percentage> should be part of the color space definition, not special-cased into the code like this.