KDE's Krita painting application back in the day was one of the first to support an OpenGL-accelerated canvas. After their GL support fell behind, it's now been brought up to speed by porting their graphics rendering code-paths to supporting an OpenGL 3.1 Core Profile and OpenGL ES 2.0.
Boudewijn Rempt, one of the Krita developers, has been porting the old, fixed-function OpenGL 1.3 code to supporting OpenGL 3.1 Core (not the compatibility profile) and OpenGL ES 2.0. He has written about this OpenGL porting adventure on his blog
, including showing off some of the old and new code.
While there's now GL 3.1 and GLES 2.0 support, there's still some OpenGL Krita TODO list items for those interested in helping out or digging deeper into the graphics code.