How do I make object fall on impact in Matter.js?

Question

I'm using Matter.js for some graphics and want this rectangle

let title = Bodies.rectangle(w / 2.4, height / 1.8, 300, 100, {
  isStatic: true,
})

to get isStatic: false and fall when it's hit by some circles that are raining down on it. I've done some extensive Googling, but haven't really found anything else but this:

Events.on(engine, 'collisionStart', function (event) {
  event.pairs.forEach(function (obj) {
    console.log(
      'BodyA is static: ' + obj.bodyA.isStatic + '. BodyB is static: ' + obj.bodyB.isStatic
    )
  })
})

This gives me all the collisions happening, but I haven't figured out how to set isStatic: false when something hits. Appreciate your help!

Answer 1

You can call Matter.Body.setStatic(body, false) on the body in question to make it active.

Here's an example:

const engine = Matter.Engine.create();
const render = Matter.Render.create({
  element: document.body,
  engine,
  options: {width: 400, height: 400, wireframes: false},
});

const fallingBody = Matter.Bodies.rectangle(
  200, 0, 20, 20, {
    frictionAir: 0.1,
    density: 0.8,
    render: {fillStyle: "red"},
  },
);
const wall = Matter.Bodies.rectangle(
  200, 150, 400, 20, {
    frictionAir: 0.05,
    isStatic: true,
    render: {fillStyle: "green"}
  },
);
Matter.Composite.add(engine.world, [fallingBody, wall]);

Matter.Events.on(engine, "collisionStart", event => {
  if (wall.isStatic && event.pairs.some(e => Object.values(e).includes(wall))) {
    Matter.Body.setStatic(wall, false);
  }
});

Matter.Render.run(render);
Matter.Runner.run(Matter.Runner.create(), engine);

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