GPU Particles 2D/3D in compatibility rendering sometimes don't emit on 4.2

[WagnerGFX]

Godot version

v4.2.beta3

System information

Godot v4.2.beta3 - Windows 10.0.19045 - GLES3 (Compatibility) - dedicated NVIDIA GeForce GTX 1650 (NVIDIA; 31.0.15.4592) - Intel(R) Core(TM) i7-2600K CPU @ 3.40GHz (8 Threads)

Issue description

Some of the GPU Particles nodes seem to not emit, while others do.

• This changes every time I re-open the editor, scenes or run the project.
• Duplicating the particle nodes makes the new one work in the editor, but running or reopening the scene starts the issue again.
• The issue still happens when using opengl3_angle on GL Compatibility
• This does not seem to happen on 4.1.2

particles.compatibility.emission.mp4

Steps to reproduce

The reproduction project has "main_2d" and "main_3d" scenes that show the issue, even in the editor.
You can re-open and/or run the project multiple times to see how the issue changes every time.

Minimal reproduction project

GPUParticles Compatibility.zip

[akien-mga]

I can confirm the bug. Note that the particle effect looks different in 4.1.2-stable and 4.2-beta3 (like in the video), but that seems due to a separate regression which was since fixed (4.1.2-stable and 4.x master behave similarly, aside from this bug of randomly not emitting).

Seemed typically like uninitialized memory usage, found the bug, I'll make a PR.

Thanks for the very clear bug report and MRP.