902246 - rgba + matte color conversion utility

Status: RESOLVED FIXED

(Firefox for Metro Graveyard :: General, defect)

Description

[Sam Foster [:sfoster] (he/him)]

We have a need (in bug 895519 at minimum) to take a given color and calculate a lighter tint for coloring backgrounds. To-date we've done this using the alpha-channel against a white background, but this doesn't work if the color must be opaque. Converting to the HSV color space for the calculation seems the best bet? 

I'm proposing this should land in browser/metro/modules/colorUtils.jsm

Comment 1

[Sam Foster [:sfoster] (he/him)]

Attachment: Utility methods for adding rgb(a) colors together

Adds methods to add 2 colors together, and refactors a little to allow reuse of the code that goes to/from packed number data format. 
I've tacked on the alpha channel value to the existing 8/8/8 rgb "words", in a way that I hope is expected and not-surprising. The only gotcha with doing this is that there's no way to distinguish a fully-transparent color from one with no alpha channel (i.e. fully opaque). As a fully-transparent color is an edge case, I've elected to treat all falsey alpha values (0 or undefined) as opaque.

Comment 2

[Sam Foster [:sfoster] (he/him)]

On fx-team:  https://hg.mozilla.org/integration/fx-team/rev/8dac6e09d3d6

Comment 3

[Tim Taubert [:ttaubert] (inactive)]

https://hg.mozilla.org/mozilla-central/rev/8dac6e09d3d6