Please don't use SDL2 and such as basis, or OpenGL with
glBegin+glReadPixels without FBOs and PBOs (not Pbuffers). I'm a
GL driver dev (userspace) for a smaller company, and I see too
much gore in popular software like that (gnome3 is the
most-horrific). A fully-featured GUI with GL needs only a thin
wrapper for glXGetProcAddress, GL context creation, BitBlt-like
things and font-glyph cache (or better yet, signed-distance-field
text rendering). Something like this:
Base (sans clipping, I haven't ported it from asm yet):
https://github.com/idinev/pub_toys/tree/master/Blitters/oDraw
SDF text:
https://www.mapbox.com/blog/text-signed-distance-fields/
Also, GL should be optional, just like with Qt; it introduces
noticeable lag of 16 to 48ms while being a resource hog
unnecessary for most apps. I could help with implementing the
abstraction layer and create a software blitter (I was
professionally doing such stuff before, for GUI toolkits and
stuff; but then again this stuff is trivial).
A 32-bit backing-store is always vital (DDB+GDI dibsection, GL
texture and such). Qt has it (and implemented really-well) and
that's the first pixel-related thing we should implement. BGRA8
will be the best format (blue in LSB).
A 9-cell blit will also be vital functionality.
