[BUG] Multithreading breaks particles in software renderers

[sneakernets]

GZDoom version

g4.14pre-36-ga0b0db6f6

Which game are you running with GZDoom?

Doom 2

What Operating System are you using?

Windows 10

Please describe your specific OS version

Windows 10 Pro

Relevant hardware info

i3-10110U, UHD Graphics, Vulkan 1.3, D3D 12_1 feature level, Intel(R) Display Audio

Have you checked that no other similar issue already exists?

• I have searched and not found similar issues.

A clear and concise description of what the bug is.

In any software renderer, when r_multithreaded is set to 1 as it is by default, particles render incorrectly in certain slices of the screen. I have attached two screenshots showing a blue particle fountain actor with r_multithreaded set to 1 and 0. notice how the particles seem to be "doubled" or "sliced"

Steps to reproduce the behaviour.

Explain how to reproduce

1. use Software Renderer
2. Summon or look at any particle effects
3. toggle r_multithreaded and notice the change

Your configuration

stock config with options changed to show this bug.

Provide a Log

No log generated.