GPUParticles3D flickers frozen particle at world origin (0, 0, 0) when shader material has y-billboard set

kraybit commented 1 year ago

Godot version

v4.0.beta17.mono.official [c40020513]

System information

Windows 10

Issue description

With certain settings, GPUParticles3D intermittently shows a particle at world origin with zero velocity.

These settings in GPUParticles3D caused this behavior:

Lifetime 1 s
Material Override / StandardMaterial3D / Billboard / Mode : Y-Billboard
Mesh: Quad

Quirks

Turning Y-Billboard on and off toggles the bug
Setting Lifetime for particles to 10 s makes the bug disappear "for ever", even if setting back Lifetime to 1 s (?)

gpu_particles_ybillboard_bug

Steps to reproduce

Create new Godot project
Create new scene with Node3D
Add GPUParticles3D node
Under Process Material, select New ParticleProcessMaterial
Click ParticleProcessMaterial for settings, there set Emisssion Shape to Box
Under Draw Passes / Pass 1, select New QuadMesh
Click the QuadMesh for settings, there set size to 0.1 , 0.1
Under Geomeetry / Material Override, select New StandardMaterial3D
Click StandardMaterial3D for settings, there set Billboard / Mode to Y-Billboard
Set Transform y-position to 1

At world origin (0, 0, 0) there's intermittently a particle with zero velocity.

Minimal reproduction project

gpu_particles_ybillboard_bug.zip

QbieShay commented 1 year ago

Could you re-test with apply_scale flag enabled?

kraybit commented 1 year ago

If the Keep Scale flag is enabled (In the shader material), then the bug disappears!

Enabling Keep Scale fixes bug

Does this flag have any other side-effects? Also, I couldn't find any apply_scale flag?

Calinou commented 1 year ago

I could reproduce a similar issue with the Particle Billboard mode here: https://github.com/godotengine/godot/issues/49767#issuecomment-1440500413

https://github.com/godotengine/godot-demo-projects/pull/849 also has a stray rain particle in the world origin that remains visible for a long time because of this.

QbieShay commented 1 year ago

oop sorry @kraybit . Yes, it was keep scale not apply scale :D

@Calinou particles use scale 0 to try and make particles invisible, but if keep scale is off then a new matrix is generated based on the camera matrix and the instance_custom.x as a rotation value, so the particles that should be "dead" are instead displayed at the origin (at least this is how it worked in 3.x)

Calinou commented 1 year ago

@Calinou particles use scale 0 to try and make particles invisible, but if keep scale is off then a new matrix is generated based on the camera matrix and the instance_custom.x as a rotation value, so the particles that should be "dead" are instead displayed at the origin (at least this is how it worked in 3.x)

Interesting, I thought their position would be changed to -INF, -INF, -INF (effectively ensuring they're outside the view frustum). This is what the Hide On Contact collision mode does. Should we make it scale particles to 0, 0, 0 instead of moving them?

QbieShay commented 1 year ago

I think that's what happens already, but if you don't enable scale in billboards you still see them. The inf solution sounds better

ecmjohnson commented 1 year ago

The inf solution is much cleaner (2 line change vs. 12) and doesn't have a performance impact on the billboarded materials since they don't need to even check anything

godotengine / godot