GZDomm 3.5.1_Legacy ..Gamma Correction Not Functional

GZDomm 3.5.1_Legacy ..Gamma Correction Not Functional. Recently had to switch to GZDomm 3.5.1_Legacy In Ubuntu Linux because I have an Older GL2 Only Video Card. I need a fix for the Gamma Correction settings Not Functioning in the Legacy version which did function before GL2 support was removed from it. the Legacy versions Gamma is too Dark to See or be Functional and does Not respond to settings.

Confirmed on windows, with the default settings gamma only works in fullscreen mode but not windowed. Software gamma is not working.
You could try to use hardware gamma for the time being.
I've just noticed but this problem has been in the legacy branch right from the start, seems something is missing there.

Try fiddling with the "vid_hwgamma" CVAR. It has "0, 1, and 2" as valid options, IIRC.

Software gamma correction is implemented via shader but they are disabled in legacy render path. So, if it’s about software gamma only, this is not a bug.

Definitely it's not a bug. I had gl_renderbuffers disabled to prevent crashes on my shitty old ati card and shaders don't work then.