BUG: Decals are Flickering on Some Machines

[proof88]

The decal map elements are flickering on 3 out of 5 test laptops.
It happens when the camera X or Y angle is just slightly different than 0 degree.
So it does not happen at exactly 0 degree or when either angle is much bigger, e.g. at least 2-3 degrees or more. So the issue happens when degree is close to 1.

The 3 laptops have:

• Intel HD Graphics 4400 / Geforce 820M 1 GB DDR3 (Tibi HP 250 G3);
• Intel HD Graphics 5500 / Geforce 940M 2 GB DDR3 (Ágoston Asus X555L);
• Intel HD Graphics 5500 / Geforce 930M 2 GB DDR3 (Adri Toshiba Satellite).

I just noticed I have to check which GPU was used on these during the test.

Update:
in all cases it was the integrated Intel HD Graphics GPU was used.
However, after forcing the Geforce GPU to be used, issue went away on 2 laptops. I could not set this on the 3rd laptop because nVidia Config GUI is not installed there, only Intel's Config tool which does not provide this selection.

Seems that newer Intel GPUs don't produce this issue: Intel UHD Graphics 620 with GL driver version: build 31.0.101.2111 is working fine.

So overall, the problematic GPUs:

• Intel HD Graphics 4400, had GL driver version: build 20.19.15.4531.
• Intel HD Graphics 5500, had GL driver version: build 20.19.15.5107 and .5126 on the other laptop.

[proof88]

So looks like for some GPU most probably I have to deviate from the values I use now for glPolyOffset in PURE.
I remember back in the old days there were vendor-specific values for games:
ValveSoftware/halflife#415

Just I did not expect I have to do this for modern Intel GPUs in the problematic cases.

[proof88]

This bug will be fixed in PURE, for that a separate ticket is opened: proof88/PGE#16 .