ZDoom

About the third issue i can't reproduce it, both with truecolor software and hardware render modes. For me there are no "hiccups", the game runs well even with them enabled and this is ultra lowend amd hardware. Must be a problem with your graphics driver. So closing as duplicate.

Yes, OpenGL backend. If I enable post-proccessing effects for example, it starts to happen, if I disable, it's still there until I quit and restart.

No, it doesn't happen. LZDoom has an older version of the software renderer and that code is not there. Not with vid_renderer 0, vid_rendermode it's in only for compatibility with some smarter mods. It happens with the hardware renderer when you look up or down as always.
Besides you should open a different thread for each issue, the first two are duplicates and the third one is about "any rendering option". I can't reproduce it, could you name a single option that makes it happen? Which backend? OpenGL?

Just for the record, latest LZDoom also has the bouncing torches but not the hiccups.

Yes, the bouncing happens with Doom, Heretic and Hexen torches. Changing sprite clipping mode makes no difference.
3rd issue happens with Truecolour software renderer, with or without hq resize modes whenever I change any rendering option, but if I quit and restart the game, it's gone, so it's not critical.

The bouncing happens in the Carmack software renderer and i can't fix it, only dpJudas or randi could i think. It's not that bad tough and i've noticed it also happens in the hardware renderer at extreme horizontal/vertical angles. I also noted in that thread it happens with Doom torches too.
The first two issues are duplicates the third is too vague. Which rendering options? HQ resize mode?

Change sprite clipping mode and see if it fixes the bouncing.

I think the first issue is a duplicate of this bug:
viewtopic.php?f=56&t=68042

Exactly, but it's not limited to Heretic.

I remember reading something related to the second one for the SW renderer.

Yes, but I didn't try much of the hardware rendering because it runs too slow on my system, at least with the same eye candy turned on in SW.

About the third one please elaborate, with vanilla you mean SW?

SW mode, truecolour renderer. The hiccups stop if I quit and restart or switch to 8-bit classic renderer.

I think the first issue is a duplicate of this bug:
viewtopic.php?f=56&t=68042
I remember reading something related to the second one for the SW renderer.
About the third one please elaborate, with vanilla you mean SW?

Hello,
I'm using GZDoom 4.4.2 64 bits build and I noticed that all fire animated sprites keep "bouncing" up and down in all games I tested (Doom, Heretic and Hexen). I'm using True Colour SW Rendering and trying different scaling options didn't fix it.
This other one I'm sure it was asked before here, but I was just wondering if a definitive fix was found: sprites above a ceiling or below a floor are visible despite being behind it (most noticeable, a barrel on Doom2 E1M2).
The last one is a minor thing: If I change anything related to the rendering, the game starts to "hiccup" and I have to switch to the Vanilla rendering to make it stop, or quit and run it again.