Collide
Bounce particles off an object, every object in a collection, or a flat ground, and send the ones that hit on to another event.
Bounce off an object, a collection's objects or the ground, friction slowing their sliding and their spin where they touch. The ones that hit go along the wire.
- Add it
- EventAdd OperatorTestsCollide
- Sends on
- Along its wire: particles that hit.
- Influence
- No: a value can’t weigh it.
When to use it
Whenever particles should meet something: a floor to land on, walls to hold liquid, a table for rigid bodies, a pole for a flag. It's also a test: wire it to another event, and the particles that hit go there, to splash, stick, change colour or vanish.
Set it up
Name what they bounce off: an Object, a Collection (every object in it with a surface), the Ground, or any of the three together.
Settings
As the flow editor’s sidebar shows them. Changing any of them marks the bake old; those marked Keyframable can also change through a bake.
How hard liquid sticks to it, in g: 1 holds a thin film up against gravity. 0 for none.
A vertex group or attribute (0 to 1) stickiness is times. Empty for all over.
Shown when Stickiness is above 0.
Keep where the liquid has wetted it, for its material (vecflow_wet), and where its surface meets it (vecflow_waterline)
How long a wetted part takes to dry to half (s). 0 stays wet.
Shown when Wet Map is on.
What they hit
- Object: a mesh, curve, surface, text or metaball, as it is in the scene, with its modifiers. Not another particles object.
- Collection: every object in it, and in the collections inside it, that has a surface. Add and remove objects without touching the flow.
- Ground: a flat floor, without end, at Height on the world's Z.
Colliders can move, turn and deform as much as you like: keyframes, parents, armatures and modifiers all count. Each step follows a collider from where it was to where it's going, so neither fast particles nor fast colliders pass through.
A mesh is hit from both its sides, so a plane is a wall and an open box is a tank.
Bounce and Friction
Bounce is the share of the speed into the surface they keep: 0 lands dead, 1 bounces back as fast as it came. Friction is the share of the speed along the surface they lose on each hit: 0 slides on, 1 stops sliding. Friction also slows their spin where they touch, so what lands stops tumbling.
At their centres
Particles meet a surface at their centres, so a sphere drawn round one sinks into the surface by its radius. Bumping particles (Particle Physics) rest on the Ground by their radius, but meet a mesh at their centres: for a floor under a heap of grains, use the Ground.
The wire
Particles that hit go along the wire at the end of that substep, and leave this event. Not wired, they bounce and stay. A Collide is a test like the others: the first test in the stack that picks a particle out wins.
Works with
- More than one: an event can hold several Collides, each with its own Bounce, Friction and wire. Collides are per event: give each event the ones its particles need.
- Bind: bound particles are held out of colliders and slide on them by their friction, without bouncing, so cloth drapes and holds on a slope.
- Rigid Body: bodies hit the event's colliders as solid shapes.
- Liquid: the colliders are the liquid's walls, and moving ones carry it.
- Follow Curve (not steered), Goal and Pin take particles through anything, so a Collide in their event does nothing to them; Follow Curve and Goal can't share an event with one.
- Smoke and fire go round colliders of their own: the Smoke and Fire panel's Colliders.
Problems you may see
event: operator needs an object, a collection or the ground
event: operator: 'collection' has nothing to collide with
event: operator: 'object' has no surface to collide with
Errors stop a bake; warnings don’t. Every message is on the Messages page.
Related
Set Value
Set one of the flow's values, or a particle's own position, velocity, speed, scale, colour, spin or shape, from a number, at random, from something else the particle has, or from the smoke and fire where it is.
Age Test
Send particles on to another event when they reach an age, since birth or since entering this one.