Rgba support

[nick87720z]

Besides core rgba support I tried to implement support for arbitrary hex color string length (though limited by maximum unsigned length for given machine), as well as rgba() and rgb() formats, using scanf.

What's also interesting, adjacent non-overlaping areas are better to be combined in additive mode, so that fading out pixels at bounds mix correctly. I'm not sure though, if cairo uses alpha channel correctly (must be summed too, not like how it does with multiply op), but at least it removes artifacts between frame and background, visible when both are equally contrast with background.

Btw, imho colors are better to be parsed once on theme loading instead of on each draw().

[codecov-commenter]

Codecov Report

Merging #717 into master will decrease coverage by 0.16%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #717      +/-   ##
==========================================
- Coverage   65.91%   65.74%   -0.17%     
==========================================
  Files          29       29              
  Lines        5102     5115      +13     
==========================================
  Hits         3363     3363              
- Misses       1739     1752      +13     

Flag	Coverage Δ
#unittests	65.74% <0.00%> (-0.17%)	⬇️

Impacted Files	Coverage Δ
src/draw.c	0.00% <0.00%> (ø)

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[tsipinakis]

The comment I posed in #713 still applies here. I don't see a reason to support so many different formats. #RRGGBBAA is widely used and and I don't think adding more provides any sort of useful functionality. In fact, the opposite, it unnecessarily increases code complexity and adds more things that may break without anyone realising. 'Less is more' as they say.

The docs indeed did claim #RGB support, but given that no-one has complained thus far that it doesn't work, my reaction would be to fix the docs rather than implement it.

[nick87720z]

Hm, let assume FP format and hex string generic parsers are too complex.
But as for #RGB, it looks two times more readable than #RRGGBB. At least I started to use it where is possible :] .

I could undo back to switch(len) variant. It is still necessary to differ between #RRGGBBAA and #RRGGBB, unless you are going to break compatibility - with original code RRGGBB will be GGBBAA :) . IMHO, there is nothing complex in hex_to_color() taking digits-per-channel parameter.

[nick87720z]

ping? At least one (my) vote for #RGB/#RGBA hex code support :)
Or you want it in same form as pre-rgba, with exception that it now expects full 32-bit value?

[tsipinakis]

Excuse the delay.

I could undo back to switch(len) variant.

That's what I had in mind. After thinking it over I'm fine with merging #RGB support given it requires minimal changes to the parsing.
However the other variant was too long and complex in my opinion which is why I said better to keep it simple.

All in all, LGTM!