Javascript 在Matter.js中添加从点A到另一个约束的约束

const engine = Matter.Engine.create();

const render = Matter.Render.create({
  engine,
  element: document.body,
  options: {
    width: 800,
    height: 600,
    wireframes: false,
    background: "#fafafa",
  },
});

const base = Matter.Bodies.rectangle(400, 100, 350, 20, {
  isStatic: true,
  render: {fillStyle: "#2e3276"},
});

const sideBase = Matter.Bodies.rectangle(280, 280, 20, 350, {
  isStatic: true,
  render: {fillStyle: "#2e3276"},
});

const ball = Matter.Bodies.circle(300, 300, 20, {
  density: 0.04,
  frictionAir: 0.005,
  restitution: 0.8,
  friction: 0.01,
  render: {fillStyle: "#4CAF50"},
});

const pendulum = Matter.Constraint.create({
  pointA: {x: 400, y: 100},
  bodyB: ball,
  render: {strokeStyle: "#000000"},
  length: 170,
});

const lineAnchor = Matter.Bodies.circle(0, 0, 0, {
  isStatic: true,
  isSensor: true,
});

const spring = Matter.Constraint.create({
  pointA: {x: 280, y: 200},
  bodyB: lineAnchor,
  stiffness: 0.0001,
  render: {strokeStyle: "#000000"},
});

Matter.Composite.add(engine.world, [
  base,
  sideBase,
  ball,
  pendulum,
  spring,
  lineAnchor,
]);
Matter.Runner.run(engine);
Matter.Render.run(render);

const findXCoordinate = (x1, y1, x2, y2, y) => {
  // slope
  const m = (y2 - y1) / (x2 - x1);

  // y-intercept (b)
  const b = y1 - m * x1;

  // x-coordinate when the line passes through y
  const x = (y - b) / m;
  return x;
};

Matter.Events.on(engine, "afterUpdate", () => {
  const {x: x1, y: y1} = ball.position;
  const {x: x2, y: y2} = pendulum.pointA;
  const {y} = spring.pointA;
  const x = findXCoordinate(x1, y1, x2, y2, y);
  Matter.Body.setPosition(lineAnchor, {x, y});
});

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