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
tx	Float	0.0	Translate X — position along the world X axis, metres.
ty	Float	0.0	Translate Y — position along the world Y axis (up), metres.
tz	Float	0.0	Translate Z — position along the world Z axis, metres. The camera looks down −Z.
rx	Float	0.0	Rotate around X, degrees.
ry	Float	0.0	Rotate around Y (turntable), degrees.
rz	Float	0.0	Rotate around Z (roll), degrees.
sx	Float	1.0	Scale along X. 1 = unchanged.
sy	Float	1.0	Scale along Y.
sz	Float	1.0	Scale along Z.
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	The frame the simulation begins — before it, nothing exists. Scrubbing anywhere replays from here, so the answer is the same whether you played or jumped.
fps	Float	24.0	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	200.0	Particles born per second. The count settles at roughly birth_rate × life once the system is running.
max_particles	Int	20000	A hard ceiling — emission stops here rather than growing without bound, so the cost stays predictable.
emitter	Choice	point	Where particles are born: a `point`, a flat `card`, the surface of a `sphere`, or the volume of a `box` — sized by `emitter_size`. `pointcardspherebox`
emitter_size	Float2	[1.0, 1.0]	The emitter's extent in world units (width and height; the sphere and box use the first as radius / half-size).
speed	Float	3.0	Initial speed along `direction`, world units per second.
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	0.0	The X of the emission direction (normalised with Y and Z).
direction_y	Float	1.0	The Y of the emission direction — up by default.
direction_z	Float	0.0	The Z of the emission direction.
life	Float	3.0	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	Random spread on each particle's lifetime, as a fraction of `life`: 0.3 means ±30 %.
size_birth	Float	0.05	A particle's size when born, world units.
size_death	Float	0.01	A particle's size at the end of its life — it interpolates between the two.
color_birth	Color	[1.0, 0.6, 0.25, 1.0]	A particle's colour when born.
color_death	Color	[0.35, 0.1, 0.05, 1.0]	A particle's colour at the end of its life, faded to over its lifetime.
gravity_x	Float	0.0	The X of the constant acceleration on every particle, world units per second².
gravity_y	Float	-9.81	The Y of gravity — −9.81 is Earth, down.
gravity_z	Float	0.0	The Z of the constant acceleration.
drag	Float	0.1	How quickly particles lose speed to the air — 0 coasts for ever, 1 stops within a second.
turbulence	Float	0.0	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	The feature size of the turbulence field in world units — small is jitter, large is slow eddies.
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	0.0	The height of the floor particles bounce off (when `bounce` is on), world units.
restitution	Float	0.4	How much speed survives a bounce: 0 sticks, 1 bounces back to full height.
friction	Float	0.25	How much sideways speed a bounce takes away: 0 slides freely, 1 stops dead on landing.
attract	Float	0.0	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	0.0	The X of the attractor's position, world units.
attract_y	Float	0.0	The Y of the attractor's position.
attract_z	Float	0.0	The Z of the attractor's position — `attract` sets the pull toward it (negative repels).
vortex	Float	0.0	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	4.0	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	4.0	Image emission: the height in world units the wired `emit` image is stretched over (its brightness is the birth-probability map).
disabled	Bool	false	Bypass: the node passes its first input through untouched (D in the graph). The knobs keep their values for when it comes back.
label	Text		A note shown under the node in the graph — what this node is FOR. Never affects the render or the cache.
hide_input	Bool	false	Draw the node without its input wire — a tidy graph for a node whose source is obvious (a Dot, a viewer tap).

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.