Bind
Hold particles together: cloth, ropes, soft bodies, sticky goo and things that tear; and hold rigid bodies on joints, or glue them into something to smash.
Hold particles together: soft bodies, ropes, cloth, sticky goo, things that tear. Binds hold wherever the particles go, until they break. Rigid bodies they hold turn on joints: chains, doors, ropes with crates. Particles losing a bind go along the wire.
- Add it
- EventAdd OperatorPhysicsBind
- Sends on
- Along its wire: particles losing a bind.
- Influence
- No: a value can’t weigh it.
When to use it
| Make | Binds | For |
|---|---|---|
| Mesh Edges | Particles born on a mesh's vertices, along its edges and across its faces | Cloth, flags, curtains, ropes and cables |
| Nearest | Each particle entering the event to its nearest within Distance, up to Max | Soft bodies: fill a shape with particles and bind them |
| On Touch | Any two that come within Distance, all the time | Sticky goo, snow that clumps, things that glue on contact |
| Chain | Particles one after another, in the order they come | A rope paid out from a moving emitter |
| Pieces | Pieces of a mesh born On Pieces, to the pieces they touch | Walls, statues and anything to smash, with Joint Glue |
A bind keeps two particles at the distance they were when it was made. It holds wherever they go, from event to event, until it breaks or one of them is deleted. Nearest and On Touch bind to the particles of every event with a Bind.
Set it up: cloth
Make the cloth as a mesh: a subdivided plane, about 30 to 60 vertices across.
In an event, add a Birth with Mode On Vertices and the mesh as its Object, then Gravity, Bind with Make Mesh Edges, and a Collide with what it falls on.
To hang it by its corners, paint a vertex group on them and add a Group Test sending them to an event with Pin.
Bake. The cloth plays as a copy of your mesh, “mesh (VecFlow)”, with its UVs and materials; torn cloth shows holes.
A mesh with only edges (a curve converted to a mesh) makes a rope. Its output object can show it as a tube: set Thickness and Material on its VecFlow Mesh modifier.
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.
Which particles get bound together.
- Nearest: Particles entering the event bind to their nearest within the distance.
- On Touch: Particles keep binding to any that come within the distance: sticky.
- Chain: Particles entering bind one after another, in the order they come: a rope.
- Mesh Edges: Particles born on a mesh's vertices bind along its edges (and across its faces): cloth and ropes.
- Pieces: Particles born as pieces of a mesh bind to the pieces they touch, holding harder over a bigger face. With Joint Glue: a wall to smash.
How far: to the object for a test, between particles for a bind, or along the ray for a raycast.
Shown when Make is Nearest or On Touch.
1 holds the length exactly; lower gives and springs back, softer and softer.
Shown when Spring is 0.
Real springs instead of Stiffness: how hard each bind pulls, in newtons, stretched to twice its length. Heavier particles then stretch them further: cloth weighs its area at its Density, Physics balls their own, others a 10 cm ball of water. 0 uses Stiffness.
How heavy the cloth is, in kg per square metre: silk 0.05, cotton 0.15, denim 0.4, canvas 0.6, rubber sheet 1.5. Used with Spring.
Shown when Make is Mesh Edges, and Spring is above 0.
How much cloth or a rope resists bending. 0 folds freely, and sharp folds can stand up and wobble; higher lies smoother and calmer; 1 keeps the shape it was born in.
Shown when Make is Mesh Edges.
A bind breaks when pulling or pushing harder than this (holding a hanging particle takes 9.81). 0 never.
The cloth or rope can't pass through itself, or through other cloth and ropes with this on. It folds and piles up. Slower.
Shown when Make is Mesh Edges.
How far apart layers keep when they touch. Parts this near each other on the mesh as it was born don't collide.
Shown when Make is Mesh Edges, and Self Collision is on.
Cloth, a rope or a soft body that comes to rest sleeps: once all of it has moved slower than this for half a second, it holds perfectly still and costs nothing until something touches it or pulls it differently. 0 never sleeps.
Times overlaps and contacts are pushed apart, and binds pulled back, each substep. More holds piles and stacks up and binds tighter; slower.
How binds hold rigid bodies, to each other or to particles.
- Ball: Rigid bodies turn freely about the point between them (a particle's centre)
- Hinge: Rigid bodies turn about the point between them only round an axis: a door, a wheel, a seesaw.
- Slider: Rigid bodies slide along an axis through the point between them, without turning: a drawer, a piston, a lift.
- Fixed: Rigid bodies hold together as they are, neither turning nor sliding: welded.
- Glue: Rigid bodies bound together are one rigid body, exactly as they were, until something strikes a piece harder than the Break Impulse, or the load inside passes the Break Load or Torque: walls, statues, beams, anything to smash.
The axis a hinge turns round, or a slider slides along.
- X: The first rigid body's own X axis, as the bind was made.
- Y: The first rigid body's own Y axis, as the bind was made.
- Z: The first rigid body's own Z axis, as the bind was made.
Shown when Joint is Hinge or Slider.
Keep a hinge's turn, or a slider's travel, between two limits.
Shown when Joint is Hinge or Slider.
How far a hinge may turn back from where it was made.
Shown when Joint is Hinge, and Limits is on.
How far a hinge may turn on from where it was made.
Shown when Joint is Hinge, and Limits is on.
How far a slider may slide back from where it was made.
Shown when Joint is Slider, and Limits is on.
How far a slider may slide on from where it was made.
Shown when Joint is Slider, and Limits is on.
A motor drives a hinge at this many radians a second, or a slider at this many metres a second.
Shown when Joint is Hinge or Slider.
The most a motor pushes with: newton metres for a hinge, newtons for a slider. 0 for no motor.
Shown when Joint is Hinge or Slider.
A joint (holding rigid bodies), or glue, breaks holding with more than this many newtons: a 1 kg weight hangs by 9.81. 0 never.
A joint's load is averaged over this long, so a sudden knock counts for less than a steady pull.
Shown when Break Load is above 0 or Break Torque is above 0.
An overloaded joint lasts this long at twice its Break Load or Torque before it breaks, longer nearer them. 0 breaks at once.
Shown when Break Load is above 0 or Break Torque is above 0.
Glue breaks around a piece struck harder than this many newton seconds: a 1 kg ball hitting at 10 m/s strikes with about 10. 0 never.
Shown when Joint is Glue.
For a fracture cut again: glue inside each piece of the first cut holds this many times as strongly, so chunks break off whole before they shatter.
Shown when Make is Pieces, and Joint is Glue.
Stiff or springy
Stiffness 1 holds each bind's length exactly; lower gives and springs back, softer and softer. On its own, a bind at 0 springs back about twice a second, at 0.5 about 20 times. It's the same however heavy the particles are.
For real weights, set Spring above 0 instead: each bind then pulls with that many newtons when stretched to twice its length, and heavier particles stretch it further. Cloth then weighs its area at its Density (in kg per square metre: silk 0.05, cotton 0.15, denim 0.4), so the same spring holds silk taut and lets canvas sag.
Damping is how fast wobbling dies down: 1 stops it.
Bend
For cloth and ropes (Mesh Edges), Bend is how much they resist bending. 0 folds freely, but sharp folds can stand up and wobble; 0.3 lies smooth and calm; 1 keeps the shape it was born in. A finer mesh bends more easily at the same Bend.
Self Collision
With Self Collision, cloth and ropes can't pass through themselves, or through other cloth and ropes with it on: cloth folds and piles, ropes coil. Layers keep Thickness apart. It's slower: switch it on for drapes, crumples and piles, not for a flag.
Tearing
A bind breaks when stretched past Break Stretch times its length (above 1; 0 never), or when pulling or pushing harder than Break Force: 9.81 is what holding one hanging particle takes, so a bind with Break Force 20 holds about two. Variation spreads each bind's limits by up to that share either way, so tears wander instead of running straight.
Particles losing a bind go along the wire: send them to an event that colours them, or deletes them.
Sleep and Rounds
Cloth, a rope or a soft body that comes to rest sleeps: once all of it has moved slower than Sleep Below for half a second, it holds perfectly still and costs nothing until something touches it or pulls it differently. 0 never sleeps.
Rounds is how many small steps a substep is cut into for the binds. More holds them tighter and stretches cloth less; slower.
Joints: binds on rigid bodies
When a bind holds rigid bodies (to each other, or to particles), Joint says how:
| Joint | Bodies | For |
|---|---|---|
| Ball | Turn freely about the point between them | Chains, ropes with crates, ragdoll-ish links |
| Hinge | Turn only round Axis | Doors, wheels, seesaws, flaps |
| Slider | Slide along Axis, without turning | Drawers, pistons, lifts |
| Fixed | Hold together as they are | Welds |
| Glue | Are one rigid body, until struck or loaded too hard | Walls, statues, beams: anything to smash |
The Axis is the first body's own X, Y or Z as the bind was made. Limits keeps a hinge's turn, or a slider's travel, between Lower and Upper. A Motor drives a hinge at Motor Speed radians a second (a slider, metres a second), pushing with at most Motor Strength: newton metres for a hinge, newtons for a slider.
Joints break by load: Break Load in newtons (a 1 kg weight hangs by 9.81), Break Torque in newton metres, averaged over Load Over so a sudden knock counts for less than a steady pull. With Endure, an overloaded joint holds that long at twice its limit, longer nearer it.
Glue also breaks around a piece struck harder than Break Impulse, in newton seconds: a 1 kg ball hitting at 10 m/s strikes with about 10. That's what breaks a wall where a ball hits it. See Destruction.
Works with
- Birth On Vertices for Mesh Edges, On Pieces for Pieces, in the same event.
- Group Test and Pin to hold cloth by some of its vertices.
- Collide: bound particles are held out of the event's colliders and slide on them by their friction, so cloth drapes over a ball and holds on a slope.
- Liquid in another event: cloth holds water and is pushed by it.
- An event takes one Bind, and can't also hold a Liquid, Follow Curve or Goal. For two kinds of binds, use two events.
Problems you may see
event: operator: an event takes only one
event: operator: Break Stretch must be above 1, or 0 never to break
event: operator: Distance must be above 0
event: operator: its Lower limit is above its Upper
event: operator: Mesh Edges binds particles born on vertices in this event; it has no Birth On Vertices
Bind with Make Mesh Edges ties particles born by Birth On Vertices. Add one, or pick another Make.
event: operator: Pieces binds particles born as pieces of a mesh in this event; it has no Birth On Pieces
Bind with Make Pieces glues pieces born by Birth On Pieces. Add one, or pick another Make.
Errors stop a bake; warnings don’t. Every message is on the Messages page.
Related
Flock
Particles move together as a flock of birds or a school of fish: keeping apart, heading the same way, staying together, and turning aside from what's ahead.
Rigid Body
Make particles solid bodies that tumble, hit each other, stack and come to rest: bricks, crates, rocks, debris, dice; each the shape it shows.