Rough sdl2 backend and painter

[tedsteen]

I needed egui to render and take input from SDL2, I did a rough implementation and would like to share it and this was the best way I could do that.

It's rough but might be a good starting point if someone would like to take it all the way.
The important stuff is here

I made two versions of the example a basic one and one that fixes this sdl2 resize "issue", it's over here

• Related to egui_glow: add SDL2 and others as an alternative to glutin #820

[tedsteen]

Sorry, that was a mis-click. Can't put it back to draft unfortunately..

[Mingun]

@tedsteen, convert to draft link located in Reviewers section on the right side:

[emilk]

See also:

• https://github.com/ArjunNair/egui_sdl2_gl
• https://github.com/ComLarsic/egui_sdl2_platform

[tedsteen]

See also:

• https://github.com/ArjunNair/egui_sdl2_gl

• https://github.com/ComLarsic/egui_sdl2_platform

They where a great inspiration! But i wanted the glow + input through sdl2 and figured that a combo like that would be suitable for this repo, also considering the linked issue/discussion.