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Rope physics

Free packv3.0.0-02D and 3DPhysics

Ropes, cords and chains that swing, drape, stretch, snap and get cut. A rope carries weight, ties to fixed points, moving hooks or rigid bodies, and is cut by a swipe, in 2D or 3D. Rope games, from rope-cutting puzzles to bridges and cranes, build on it.

This is a Free pack. Every phaser.io account can use it in their games.

Released October 19, 2026

Rope physics: a screenshot of its demo
A note about these graphics

Expansion packs don't come with graphics. This screenshot is one way of drawing what the pack does, made for its demo: none of the sprites, tiles or backgrounds in it are in the pack.

That's by design. A pack is a game's logic, mechanics and effects, and it works with whatever art you give it. Some packs draw effects, backdrops or 3D scenes of their own, but none carries a game's sprites.

So the look is yours. Make the art on phaser.io, bring your own, or let your agent draw it in code: the same pack can look like anything.

What it does

A rope is a strand of particles with mass, held by XPBD stretch and bend constraints. That is the model a rope game needs: the rope keeps its swing when the thing on it moves, drapes over pegs and boxes with friction, stays its length or stretches like a bungee as you choose, and tears past a tension you set. An inextensible rope is also held by long-range tethers to its held ends, so a heavy load on a light rope does not stretch it.

You add ropes and loads to a RopeWorld: game.ropes when the pack is composed, or one of your own from createRopeWorld. Each end ties to a free point, a fixed point, a load (with its own radius, mass and gravity scale, so a bubble can lift it), a point that follows a function (a rotating hook, a trolley), or a rigid body in another physics pack, through a link that reads where the body is and pushes it with impulses. Static colliders, from circles and capsules to polygons, chains of walls and planes, stop ropes and loads with Coulomb friction.

Cutting is the rope game's verb: cutAlong(path) cuts every segment a polyline crosses, tested against this step's positions and the last's, so a fast slash cannot slip between two frames of a thin rope. Each step is split into as many substeps as the fastest particle needs rather than capping its speed, and diagnostics() says when that ran short. The world draws nothing: runs() gives the uncut stretches of each rope as polylines to draw.

Features

  • Real rope behaviour — swing, drape, stiffness from bend, give from stretch, and a tear tension.
  • Ends of every kind — free, fixed, a load, a moving follow point, or a link to a rigid body.
  • Loads — radius, mass and a live gravity scale, with impulse and place, for candies, crates and buckets.
  • Colliders — circles (spheres in 3D), capsules, boxes, convex polygons, chains and planes, each with friction.
  • Swipe cutting — cutAlong across two steps, cut(segment), and nearest for pressing on a rope.
  • Winches — payOut lets a rope out or reels it in, and attach moves an end.
  • Events — cuts, by call, swipe or tear, and a load's first contact with a collider.
  • Diagnostics — substeps, saturated steps, the largest stretch and tension, kinetic energy and whether it has settled.
  • Saves — snapshot and restore the whole world as plain JSON.
  • 2D or 3D — flat in the z = 0 plane with gravity of 900 down in a 2D world, all three axes with 9.81 down in 3D.
  • Rope contact — optionally, ropes collide with each other and with loads, for tangles and draping.

Good for

  • Rope-cutting puzzles in the style of Cut the Rope, where a candy hangs on several ropes.
  • Cranes, winches and tow lines — a rope from a moving trolley to a crate body, paid out and reeled in.
  • Rope bridges — a rope between two fixed points, with planks along it.
  • Hanging scenery — lamps, vines and chains that sway and react to the player.
  • Bungees and swings — elastic ropes that stretch further under heavier loads.
  • 3D games — ropes in all three axes, tied to physics-3d bodies.

Make it yours

The world's options are gravity, step (1/120 second), iterations (8 passes a substep), maxSubsteps (16), damping (0.2 a second), ropeContact (off), flat, and limits on particles, ropes, colliders and events (8192, 512, 1024 and 256), which make a runaway level fail loudly rather than grind. Every rope chooses its length or slack, radius, segment count, mass, stretch and bend compliance and tear tension.

Two different uses: a candy on two inextensible ropes from fixed hooks, cut by swipes, its gravity scale turned negative for a bubble and impulses for air cushions; and a 3D crane whose rope follows a moving trolley and links to a crate in physics-3d, let out and reeled in with payOut.

A quick look

A load on two ropes, cut by a swipe, lifted, puffed and drawn:

const candy = game.ropes.addLoad({ id: 'candy', x: 240, y: 300, radius: 18, mass: 10 });
for (const [id, x] of [['left', 120], ['right', 360]] as const)
    game.ropes.addRope({ id, from: { fixed: { x, y: 100 } }, to: { load: 'candy' }, radius: 3, slack: 0.1 });
game.ropes.cutAlong(swipePoints);      // cut what the swipe crossed, this step or the last
candy.gravityScale = -0.3;             // a bubble lifts it
candy.impulse(400, -200);              // an air cushion puffs it
for (const e of game.ropes.drain()) if (e.kind === 'cut') playSnip();
for (const r of game.ropes.ropes()) for (const run of r.runs()) drawLine(run);   // [x0, y0, z0, x1, …]

Works with

  • physics-2d, physics-box2d and physics-3d — rigid bodies a rope end can be tied to; ropes step after them.
  • cut-rope — the complete rules of a rope-cutting puzzle, built on this pack.
  • rope-untangle — untangling puzzles, which use these ropes for feel.
  • rope-swing — a weightless grappling rope for a body to swing on, wrapping round corners.

Good to know

  • Particles collide with colliders, not segments: keep segments about two radii long, the default, so a thin peg cannot pass between them.
  • payOut keeps the particle count, so a rope can grow to four times and shrink to a fifth of the length it was made with; make a new rope for more.
  • A body link is coupled once per game step, so a very light body on a very heavy rope is still dominated by the rope.
  • Swipes cut in the xy plane; in 3D, project the pointer's path onto it, or cut with nearest.
  • After restore, moving and linked ends come back fixed where they were; attach them again.

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