gles2: custom shaders

[Drakulix]

Adds first-party support for shader-based render elements.

Refactors a few things in the process:

• Combines our three fragment texture shaders into one and compiles it multiple times with corresponding #defines.
• Adds another debug shader permutation for debug_flags

TODO:

• Add the same option for custom texture shaders
• Add custom-texture-shader RenderElement wrapper

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (7fcc80a) 23.81% compared to head (c227847) 23.81%.

❗ Current head c227847 differs from pull request most recent head e949a02. Consider uploading reports for the commit e949a02 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #901   +/-   ##
=======================================
  Coverage   23.81%   23.81%           
=======================================
  Files         131      131           
  Lines       20810    20810           
=======================================
  Hits         4955     4955           
  Misses      15855    15855           

Flag	Coverage Δ
wlcs-core	20.90% <ø> (ø)
wlcs-output	8.94% <ø> (ø)
wlcs-pointer-input	23.06% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[PolyMeilex]

If our shaders are now nicely combined, would it make sense to move them to .vert, .frag files, and include_str! them, to get proper syntax highlighting and editor support?

[Drakulix]

If our shaders are now nicely combined, would it make sense to move them to .vert, .frag files, and include_str! them, to get proper syntax highlighting and editor support?

Sure thing 596c4d0

[cmeissl]

I really like that approach and the flexibility it introduces 👍