[1.8 onwards] rendering glitch with fast projectiles

[HexaDoken]

A projectile going sufficiently fast will glitch and sometimes fail to render. Sometimes, it will be only visible from certain angles, sometimes, invisible at all.

"Sufficiently fast" in this case seems to begin at about 100. The faster the projectile is, the more glitchy it's rendering will be.

There is no relation between this bug and the projectile inheriting from FastProjectile or not. Both will glitch as long as they are sufficiently fast.

This only happens in GL renderer. Software does not have this issue.

Tested both on 1.8.02 and 2.1.pre-1159-gfbefe13. Also tested on Zandronum 2.0, which means that this problem is quite old, seeing as how it's GL renderer is based on GZDoom 1.5.0.

Minimal example wad attached. To test:

1) Go to some open, spacious map. D2MAP32 does nicely.
2) Give all in the console, select gun at slot 7.
3) Fire, then quickly freeze from the console.
4) The projectile will spawn a lot of trails so that it's position can be identified easily. Run towards it - you will see that it will be invisible from certain angles.

[Graf Zahl]

This happens because projectiles aren't rendered when they are closer toward the shooter than 'speed' map units.
The motivation was to not render them during their first tic. Unless you use a teleporter or freeze the game this should never become an issue while playing.

[Graf Zahl]

I did some tweaking of the values here which should address this problem.