behaviours-rs

Work in progress!

Rust + wasm library for declarative modeling of simple particle behaviours.

Installation

npm install behaviours-rs

Example

10000 points repelling each other:

import { createSimulation } from "behaviours-rs";

const [width, height] = [600, 600];

const numPoints = 10000;

const points = new Float32Array(numPoints * 2);

for (let i = 0; i < numPoints; i++) {
  const x = Math.random() * width;
  const y = Math.random() * height;

  points[i * 2] = x;
  points[i * 2 + 1] = y;
}

// main behaviour modeling
const behaviours = [
  ["repel", { f: 0.3, r: 50.0 }],
  ["dampen", { f: 0.1 }]
];

const simulation = createSimulation(points, 2, behaviours);

const canvas = document.createElement("canvas");
canvas.width = width;
canvas.height = height;
document.body.appendChild(canvas);

const ctx = canvas.getContext("2d");

const loop = () => {
  ctx.clearRect(0, 0, 600, 600);

  simulation.step();

  const positions = simulation.get();

  for (let i = 0; i < positions.length; i += 2) {
    const x = positions[i];
    const y = positions[i + 1];

    ctx.fillRect(x, y, 1, 1);
  }

  requestAnimationFrame(loop);
};

loop();

Running examples:

cd ./examples/
npm install
npm start

API

Constructor

const simulation = createSimulation(points, dimensions, behaviours) - creates new simulation

• points - Float32Array of flat x, y, z (if in 3d) positions: [ x1,y1,z1, x2,y2,z2, ... ]
• dimensions - 2 or 3, can be omitted, defaults to 2
• behaviours - tree of behaviours

Functions

• simulation.step() - single step of simulation
• simulation.get() - returns all positions (same format as points when creating simulation)
• simulation.getIf(test) - returns all points matching provided test (look at "if" behaviour)
• simulation.setMeta(idx, key, value) - sets additional key/value for specified point
• simulation.getMeta(idx, key) - returns value for provided key or empty string

Behaviours

• ["repel", { f, r, p }]
  • f - force, ideally between 0.0 and 1.0
  • r - impact radius
  • p - position when the repelling happens, if ommited the points repel each other
• ["attract", { f, r, p }]
  • f - force, ideally between 0.0 and 1.0
  • r - impact radius
  • p - position when the attraction happens, if ommited the points attract each other
• ["dampen", { f }]" - dampens velocity
  • f - force, ideally between 0.0 and 1.0
• ["if", { test }, children] - executes children when test passes
  • test: [op, key, value], where op is either "==" or "!=", and key/value are this point's metadata
• ["collide", { test, r }, children] - executes children when points collide in given r, optionally passing a test
  • test - same as in "if", optional
  • r - radius of collision
• ["set", { ke, value }]" - sets key/value metadata on current point

For collide and if usage look into examples/03.js.