Replace manual delays by frame time measurement

[midzer]

Hi,

According to good dialogue in #746, here's mentioned PR to improve render performance (should give more FPS) by replacing all manual delays.

Code is tested for Descent 1 Shareware.

Have a nice week
midzer

[vLKp]

From an initial read of this work, it looks like you removed delay calls in a variety of places, but only added the ability to sleep in the OpenGL-specific rendering path. Will that not cause the SDL-only build to spin, since it does not use the OpenGL renderer? It looks like SDL-only may not even build, since you changed the declaration for gr_flip, but did not update the implementation in similar/arch/sdl/gr.cpp to match the new signature.

[midzer]

Yeah, I forgot the SDL-only path.

Gonna try if I get it to work and push necessary changes.