Adjust theming color calculations using sRGB luma

[juliusknorr]

The theming color calculation is currently using the lightness of a color to decide if icons should be inverted in the app menu or not. However sRGB Luma provides a way better algorithm for deciding if black or white icons should be used on a colored background. (See https://robots.thoughtbot.com/closer-look-color-lightness for reference)

The following example shows the icon inverting the old way (on the left) and the new way (on the right): Color invert comparison old vs. new

Especially for intense color values like #FFFF00 this will provide far better results.

Fixes #7401

[MorrisJobke]

Especially for intense color values like #FFFF00 this will provide far better results.

Yes - this is awesome. I also noticed that one and nice that it is finally fixed.

[MorrisJobke]

Easier approach to write this code:

list($red, $green, $blue) = $this->hexToRGB($color);

See https://secure.php.net/manual/en/function.list.php#refsect1-function.list-examples

[codecov]

Codecov Report

Merging #7705 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #7705      +/-   ##
============================================
+ Coverage     51.18%   51.18%   +<.01%     
- Complexity    24948    24950       +2     
============================================
  Files          1605     1605              
  Lines         94923    94927       +4     
  Branches       1376     1376              
============================================
+ Hits          48584    48589       +5     
+ Misses        46339    46338       -1

Impacted Files	Coverage Δ	Complexity Δ
apps/theming/lib/Util.php	92.94% <100%> (+0.44%)	30 <4> (+2)	⬆️
lib/private/Files/Cache/Propagator.php	94.93% <0%> (-1.27%)	16% <0%> (ø)
lib/private/Server.php	81.43% <0%> (-0.12%)	134% <0%> (ø)
config/config.sample.php	0% <0%> (ø)	0% <0%> (ø)	⬇️
apps/files_trashbin/lib/Trashbin.php	72.53% <0%> (+0.24%)	136% <0%> (ø)	⬇️
lib/private/Security/CertificateManager.php	92.07% <0%> (+0.99%)	39% <0%> (ø)	⬇️

[juliusknorr]

Please review @nextcloud/theming

[nickvergessen]

This will invalidate the android app's code again?
Or did we already move this out to capabilities?

[tobiasKaminsky]

As I understand it is only a refined calculation.
On Android we use color, text color and element color for newest servers. On older servers we calculate text and element color ourselves.

[juliusknorr]

Yes, if clients use the text-color entry in the capabilities, there will be no other change required. I guess it's fine for android then. What about @nextcloud/ios ? Do you the servers text color value or do you do your own calculations.

[rullzer]

Fine by me :D

[spaeps]

I don't know if it should be better open a new issue/pull but, dealing with this topic, this is my view on choosing the right color for icons and text.

Any algorithm would not fit the best choice for every colorscheme and tastes, so I think a new custom parameter should be added in the theming app, as "Inverted" (or "Invert color" or other).

This way an user could manually choose the right foreground color, expecially when the main color is a borderline one (i.e. when a single step value changes the foreground color).

The new option would directly force the "inverted" variable value, by inverting the calculated one and definitely solve the issue forever.

If you like the idea I could open a new issue/pull, or the solution could be integrated in this pull.
Let me know.

@juliushaertl @MorrisJobke @nickvergessen @tobiasKaminsky