Request for Comments: HWB Functions

Posted 7 October 2020 by Natalie Weizenbaum

The CSS working group has been up to all sorts of exciting stuff recently in the Color Level 4 spec, and the Sass team is starting to think about how to integrate those cool new features into Sass’s color model. We need more time to hammer out exactly the right designs for complex features like the Lab color space, but that doesn’t mean we can’t add a few new color goodies.

Today we’re announcing a proposal for one such feature: built-in Sass functions for HWB colors! Once this proposal (drafted by Sass core team member Miriam Suzanne) is accepted and implemented, you’ll be able to write colors in HWB syntax and adjust their whiteness and blackness the same way you can adjust a color’s saturation and lightness today.

The Functions permalinkThe Functions

Here are the new and improved functions this proposal adds:

color.hwb() permalinkcolor.hwb()

The color.hwb() function defines a color using its hue, whiteness, and blackness. Like the existing rgb() and hsl() functions, It can either use the space-separated syntax defined in the spec (hwb(270 20% 40%)) or the more Sass-y comma-separated syntax (hwb(270, 20%, 40%)). Because HWB colors use the same sRGB colorspace as all other Sass color values, colors created this way are fully compatible with all existing Sass color functions and will be emitted as their RGB equivalents for maximum browser compatibility.

Note that unlike rgb() and hsl(), the proposal doesn’t add this function to the global scope yet. This is because Sass has a policy of never adding support for new CSS syntax before at least one browser implements it. Specs have a tendency to change until they’re locked in by browsers, and if Sass ends up supporting something different than the browsers themselves that’s bad news!

color.whiteness() and color.blackness() permalinkcolor.whiteness() and color.blackness()

These functions work like the color.saturation() and color.lightness() functions do for HSL colors. They even work for colors that weren’t created with color.hwb(), so you can use them to check how pale or dark any color is.

Because HWB colors have the same notion of “hue” as HSL colors, the existing color.hue() function already works perfectly!

color.scale(), color.adjust(), and color.change() permalinkcolor.scale(), color.adjust(), and color.change()

All three color modification functions now support $whiteness and $blackness arguments. If you want a color (again no matter how it was created) to be 20% whiter, just pass it to color.scale($color, $whiteness: 20%) and there you go!

Let us know what you think! permalinkLet us know what you think!

If you’re interested in learning more about this proposal, read it in full on GitHub. It’s open for comments and revisions for the next month, so if you’d like to see something change please file an issue and we can discuss it!