On Raspberry Pi 4 B Rasbian:
I want to change gamma for OpenGL 2.1.
xrandr and xgamma seems not working.
In yquake 2 with SDL2 or SDL 1.2 changing brightness and 'vid_gamma' not yielding any effects.
Building "WITH_X11GAMMA" (setting the gamma via X11) behave the same.
Any ideas for changing gamma on RPi4?