Rope Collider

Rope Collider lives inside a Rope System and emits a collider configuration each frame; the container collects all of them (up to 64 collision primitives per system) and the GPU solver resolves them as push-out constraints after each substep. The push-out includes a thickness margin, so cables rest on surfaces rather than sinking into them.

All shapes are XY shapes extruded along Z — a Circle is really an infinite cylinder in depth, a Box a slab. This keeps collision cheap and matches how the rope world is authored in 2D.

Four types, selected by Type, with the inspector showing only the ports each one uses:

Sculpting by hand. With Show on, the collider draws its outline in the render viewport. Line colliders additionally get draggable endpoint handles, and Alt-click adds a point — the new point is immediately draggable, so a multi-point polyline is built by clicking along the shape you want. A polyline emits one capsule segment per consecutive pair, capped at 32 segments (33 points) per collider.

Driving from data. The Points input takes a point structure (Grafit's Point N X/Y/Z convention) and rebuilds the polyline from it every frame — a Vision skeleton, a Geometry to Points contour or a Notes to Points layout becomes a live collision surface. Connecting Points auto-creates a Points macro group, which is the source of truth each frame; a handle drag temporarily takes precedence so manual edits are never fought by the data path.

Material. Bounciness (0–1) is restitution — 0 absorbs, 1 makes cables jump off. Friction (0–1) is tangential resistance — 0 lets cables slide off a tilted floor, 1 pins them where they land.

Output: Config (structure), or Configs for a polyline — collected automatically by the parent Rope System.

• Cables on the ground — Floor at Position Y −0.7 with Friction 0.6: cables fall, land and stay heaped instead of sliding out of frame.
• Draped over a bar — Line collider, Radius 0.05, positioned mid-frame with free-ended cables above it: the classic drape, with the cable sliding along the bar as Friction drops.
• Hand-drawn landscape — set Type to Line, turn Show on and Alt-click a ridge line across the viewport: cables cascade over the terrain you just drew.
• Live body collision — Vision (Body) → Landmarks to Points → system boundary → collider Points: cables drape over a moving silhouette in real time.
• Wrapping a disc — Circle collider with Radius 0.35 under a curtain of cables plus Rope Gravity: strands slide around the circumference and hang off both sides.
• Bounce chamber — a Box with Bounciness 0.8 and a Rope Attract repeller inside: cables ricochet off the container walls.

• Alt-click only builds polylines on Line colliders, and only while Show is on — the handles are the interaction surface.
• Once a polyline exists it takes priority over Start X/Y and End X/Y; delete the extra points to go back to two-point mode.
• Size X and Size Y are full dimensions for a Box (halved internally), while Radius is a true radius for Circle and Line.
• The system counts primitives, not nodes: a 20-point polyline consumes 19 of the 64 available collider slots.
• Give cables enough segments to sample a surface — a 6-segment rope stepping over a thin Line collider can tunnel through; 24 segments or a larger Radius fixes it.
• Angle on the Floor is clockwise-positive, matching every other rotation in Grafit — tilt it and cables slide downhill at a rate set by Friction.