ParticleSystem3D

3Dv1app

Overview

A deterministic particle system authored as a standard USD Points prim, so it carries velocities and per-particle ids for motion blur and id passes.

How to

Choose the emitter (point, card, sphere, box).
Shape the motion with gravity, drag and curl turbulence.
Ramp size and colour over life.

Inputs

Input	What it takes
in	the image this node works on
emit	—

Outputs

Output	Type
out	Scene

Parameters

Parameter	Type	Default	What it does
seed	Int	1	Change it for a different-but-equally-valid version of the same effect. The same seed always gives the same sim.
start_frame	Int	1	Not documented yet.
fps	Float	24	The integration step. Set it to the project rate — a sim stepped at a different rate than the timeline drifts against it; the panel warns when they disagree.
birth_rate	Float	200	Particles born per second. The count settles at roughly birth_rate × life once the system is running.
max_particles	Int	20_000	A hard ceiling — emission stops here rather than growing without bound, so the cost stays predictable.
emitter	Choice	point	Not documented yet.
emitter_size	Float2	[1.0, 1.0]	Not documented yet.
speed	Float	3	Not documented yet.
spread	Float	0.25	How wide the emission cone is: 0 is a beam along the direction, 1 is every direction equally.
direction_x	Float	0	Not documented yet.
direction_y	Float	1	Not documented yet.
direction_z	Float	0	Not documented yet.
life	Float	3	Seconds a particle lives. life_variation randomises it either side, so they don't all die on the same frame.
life_variation	Float	0.3	Not documented yet.
size_birth	Float	0.05	Not documented yet.
size_death	Float	0.01	Not documented yet.
color_birth	Color	[1.0, 0.6, 0.25, 1.0]	Not documented yet.
color_death	Color	[0.35, 0.1, 0.05, 1.0]	Not documented yet.
gravity_x	Float	0	Not documented yet.
gravity_y	Float	-9.81	Not documented yet.
gravity_z	Float	0	Not documented yet.
drag	Float	0.1	Not documented yet.
turbulence	Float	0	Curl-noise wind, in m/s². It swirls without blowing particles out of a region, which is what makes it read as air rather than a fan.
turbulence_scale	Float	0.25	Not documented yet.
bounce	Bool	false	Particles bounce off a horizontal floor at floor_y instead of falling through. Restitution is how much speed survives the hit; friction slows them along the ground.
floor_y	Float	0	Not documented yet.
restitution	Float	0.4	Not documented yet.
friction	Float	0.25	Not documented yet.
attract	Float	0	A point that pulls particles in (positive) or pushes them away (negative), at attract_x/y/z. Falls off with distance, softened at the centre so passing through it is survivable.
attract_x	Float	0	Not documented yet.
attract_y	Float	0	Not documented yet.
attract_z	Float	0	Not documented yet.
vortex	Float	0	Swirl around the vertical axis through the attract point — a tornado rather than a fan. Combine with a gentle attract for a drain.
emit_width	Float	4	How wide the emission image maps across the scene, in metres. The `emit` input's brightness decides WHERE particles are born inside it.
emit_height	Float	4	Not documented yet.
tx	Float	0	Translate X — position along the world X axis, metres.
ty	Float	0	Translate Y — position along the world Y axis (up), metres.
tz	Float	0	Translate Z — position along the world Z axis, metres. The camera looks down −Z.
rx	Float	0	Rotate around X, degrees.
ry	Float	0	Rotate around Y (turntable), degrees.
rz	Float	0	Rotate around Z (roll), degrees.
sx	Float	1	Scale along X. 1 = unchanged.
sy	Float	1	Scale along Y.
sz	Float	1	Scale along Z.

Known edges

The sim is bit-identical every time: the same seed and frame give the same answer whether you played there or scrubbed there.