Hello there!
I built a platform to ease development of graphical applications using OpenGL ES 2.0 (like the raspberry pi):
https://github.com/gbuzogany/rockette
I'm working on a custom display for my motorcycle, and had a ton of work on the way to get something nice going, so I thought about sharing it.
It already comes with a lot of glue code (loading/using shaders, loading textures, loading fonts, rendering text, receiving data from other apps), so it should simplify things a lot!
It uses SDL2 as a media layer, so you don't need a window manager to run it.
I used ANGLE to translate the OpenGL ES 2.0 calls to native calls, so you can implement/test the application in your favourite environment (mac/windows/linux), and when it's done, compile it on the raspberry (I should get cross-compilation working soon).
A quick demo of a thing I built with it:
https://wintermute.digital/dash-akira.mov
Have fun!