OpenGL shield z-fighting

One more fix that I'd like to see for .22.

Easiest to notice by grabbing the electric shield in GFZ2, then running in the water hallway. Perhaps with video res at 1280x800.

This happens to me on opengl-bsp-cleanup, float_equals, and SRB2_release_2.1.21 on both 32-bit and 64-bit. It does not happen in 2.1.20 (technically it does, but very minimally.) Did anything change since then?

@MonsterIestyn can you look at this please?

changed the description

I'm not entirely sure what could be up here offhand tbh

Here's a video of the bug.

Top-left is !237 (merged) (commit 7848e9f4); top-right is before that merge (commit 1619b392); bottom is 2.1.20.

Note the increased banding on the top-left. The banding does happen in 2.1.20, but to a way lesser extent.

So it appears somewhere in the opengl-quickfixes merge that shield banding got worse. Will try to narrow down the exact commit.

@Sryder any ideas?

EDIT: If you can play APNG, this is a more severe example from FuriousFox. Not sure if this is the same bug; but perhaps it's driver-dependent.

It could be driver dependant, I also get the same severe Z fighting problems no matter if I use 32 or 64 bits, and it isn't only with sprites; anything that stacks ontop of something else is subject to Z fight like textures.

https://giant.gfycat.com/SkeletalRevolvingAfricanpiedkingfisher.webm (here's a small webm with nice shield z fighting)

Would you see if the same Z fighting happens with this EXE? There's two in the ZIP -- try with srb2win-pre-quickfixes.exe

32-bit: srb2win-ogl-quickfixes.zip

Hm, maybe I should double check first whether shields use dispoffset to offset themselves in front of the player... I attempted to support that years back but failed to account for the very existence of z-fighting somehow. derp

@digiku it's definitely A LOT better but I still see some horizontal lines bleeding through shields.

The culprit commit is 0885d271. The prior commit 4e95066f does not exhibit this severity.

Transform sprites in world space rather than screen space

Transformation based on screen space would make sense if we didn't want anything in the world to effect the sprites.
This should allow sprite splitting and sorting of sprites with level geometry easier.

stransform is no longer needed.

I'm gonna say it's driver dependent. This is with vanilla 2.1.21, I don't get z-fighting, but I do see horizontal lines bleeding through shields.

I would bet it's the same bug for all users, just that it manifests differently for different drivers.

For me and you, horizontal lines is not too severe, albeit noticeable. The other type of z-fighting is just bad, however

Z-Fighting on things like shields and overlays, if I'm not wrong, was in the game before my change to transform sprites in world space too. Dispoffset will need to adjust the position of sprites ever so slightly to avoid it probably, I think there's an OpenGL function that could be used which would alter depth of the fragments in some way without altering position, but I can't remember what it's called. (of course, shaders would provide the ability to do the same but in a way where we would know what we're doing to it)

Azeonus/pris on Discord has been working on a fix for this just so you guys know

mentioned in merge request !395 (merged)

closed via merge request !395 (merged)

mentioned in commit 7982b169