feat: contrast util with yiq calculator

[ornanovitch]

Needed for #3653

Changes proposed in this pull request:

• The isDark utility converts a hex color to rgb, and then calcul a YIQ value in order to get the appropriate contrast value (is it dark or is it light?)
• In order to use this new snippet without any pain, I created two new color variables which aren't depending on the dark/light mode: @text-on-light and @text-on-dark

See #3653 for example

See https://www.w3.org/TR/AERT/#color-contrast for references

Reviewers should focus on:

I don't know... Is the name getContrast ok regarding your naming conventions?

Screenshot

see #3653

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests are not appropriate here.

[davwheat]

Ooh, you moved this here! Makes sense.

I left a comment about exporting an isDark util so we don't need to compare against 128 in our code in your draft PR. Could we do that here?

[ornanovitch]

I left a comment about exporting an isDark util so we don't need to compare against 128 in our code in your draft PR. Could we do that here?

You're right! I'll do it asap :)

[ornanovitch]

@davwheat It seems a lot better, thanks for your advice!

[ornanovitch]

:)

[iPurpl3x]

@ornanovitch, @imorland, @davwheat isDark throws an error and the app crashes if a color is set to NULL in the database…

[SychO9]

please open a bug report with specifics.

[iPurpl3x]

Here you go @SychO9 #3764