Follow Curve
Send particles along a curve, text or hair curves: exactly, through anything, riding it as it moves; or steered, pushed along it with the event's other forces.
Particles go along a curve, text or hair curves object at a speed, keeping how far off it they were as they entered (more or less as its radius grows or shrinks), turning round it if asked: exactly, through anything, riding it as it moves and bends. Those born along it start from there. Those reaching an open curve's end go along the wire. Steered, they're pushed along it instead, with the event's other forces and colliders.
- Add it
- EventAdd OperatorForcesFollow Curve
- Sends on
- Along its wire: particles reaching an open curve’s end.
- Influence
- No: a value can’t weigh it.
When to use it
- Particles along a path: sparks running down a wire, light trails through a logo, a stream of magic round a character.
- Spirals: with Turn Round, particles corkscrew round the curve as they go.
- Guided but loose: with Steer, particles are pushed along the curve instead, so they swing wide on fast bends and still bounce off things.
Exactly, or steered
Exactly (the default), particles are taken along the curve. Each keeps how far off the curve it was as it entered (more or less as the curve's radius grows or shrinks), and goes at Speed, through anything, riding the curve as it moves and bends. Forces and colliders in its event don't move it, so it can't share an event with Collide, Particle Physics, Bind, Rigid Body, Liquid, Flock or Pin.
Steered, particles are pushed along it instead: they come to its speed and in to it over the Response time, feeling the event's other forces and colliders. A sharp bend taken fast can throw them off. A steered Follow Curve can share an event with everything but Pin.
Set it up
Draw a curve (a Bezier or NURBS curve, text, or hair curves). Its direction is the way particles go: CurveSegmentsSwitch Direction turns it round.
Add Follow Curve to the event and name the curve in Object.
To have particles born along it, give the Birth a Position Along a Curve on the same curve: each starts from its spot.
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 fast they turn round the curve, a second, as they go along it: spirals.
From an open curve's end, back to its start (closed curves go round anyway). Those reaching the end go along the wire either way.
Shown when Steer is off.
Push them along it instead of taking them: they come to its speed and in to it over the response time, feeling the event's other forces and colliders, and a sharp bend taken fast can throw them off.
About how long it takes them to settle: no less smoothly, but no further than they must.
Shown when Steer is on.
They go free within this far of the curve (times its radius, which is 1 m unless its points or bevel change it), and are pulled in from farther.
Shown when Steer is on.
The most it changes their velocity in a second. 0 for no limit.
Shown when Steer is on.
Fades out to nothing this far from the object. 0 reaches everywhere.
Shown when Steer is on.
Speed, Variation and Turn Round
Speed is in metres a second along the curve; negative goes back along it. Variation gives each particle its own speed, up to this much faster or slower. Turn Round turns each particle round the curve as it goes, so those off the curve spiral; it does nothing to particles on the curve itself.
Ends and loops
On a closed curve particles go round and round. On an open one they stop at its end, or with Loop go back to its start and on again. Either way, particles reaching the end go along the wire, if there is one, carrying on past the end as they went.
Steer
With Steer on:
- Response is about how long they take to come to the curve's speed, and in to it: short is snappy, long is lazy.
- Tube: within this far of the curve (times its radius) they go free, and are pulled in only from farther out. 0 pulls them right onto it.
- Most caps how much it can change their velocity in a second, so a strong guide can still lose them. 0 for no cap.
- Reach fades it out to nothing this far from the curve. 0 reaches everywhere.
A steered Follow Curve can't loop: particles reaching an open end go along the wire, or are held at the end.
Works with
- Position Curve with the same curve, for births along it.
- Goal Curve: particles arriving on a curve are handed to a Follow Curve on it, right where they are.
- Speed with Add in the next event, to send them off the end with a kick.
- An event takes one Follow Curve or Goal.
Problems you may see
event: operator takes particles where they go, through anything: it can't share an event with name
event: operator: 'object' is not a curve: pick a curve, text or hair curves object
event: operator: an event takes one Follow Curve or Goal
event: operator: name holds its particles, so it can't steer them
event: operator takes particles where they go: this event's forces don't move them
Errors stop a bake; warnings don’t. Every message is on the Messages page.