js实现的模拟弹性网格布拉扯仿真动画可拉伸可切割

题目比较长，先提供一个图片看看效果

 也可以自己查看预览图 在线预览http://mubanmao.top/content/preview?id=686f9976-3c54-45b1-9e51-1a81389d5fbb

主要的js代码

let accuracy = 5,
    clothX = 60,
    clothY = 25,
    spacing = 8,
    tearDist = spacing * 4,
    friction = 0.99,
    bounce = 0.5,
    gravity = 400,
    modePull = true;
 
 
const canvas = document.getElementById("canvas"),
      ctx = canvas.getContext("2d");
 
ctx.strokeStyle = "#555";
 
const w = canvas.width = Math.min(700, window.innerWidth),
      h = canvas.height = 400;
 
const mouse = {
  cut: spacing,
  influence: spacing * 2,
  down: false,
  //button: 1,
  x: 0,
  y: 0,
  px: 0,
  py: 0,
};
 
class Point {
  constructor(x, y) {
    this.x = x;
    this.y = y;
    this.px = x;
    this.py = y;
    this.vx = 0;
    this.vy = 0;
    this.pinX = null;
    this.pinY = null;
 
    this.constraints = [];
  }
 
  update(delta) {
    if (this.pinX && this.pinY) { return this; }
 
    if (mouse.down) {
      let dx = this.x - mouse.x;
      let dy = this.y - mouse.y;
      let dist = Math.sqrt(dx * dx + dy * dy);
 
      if (modePull && dist < mouse.influence) {
        this.px = this.x - (mouse.x - mouse.px);
        this.py = this.y - (mouse.y - mouse.py);
      } else if (dist < mouse.cut) {
        this.constraints = [];
      }
    }
 
    this.addForce(0, gravity);
 
    let nx = this.x + (this.x - this.px) * friction + this.vx * delta;
    let ny = this.y + (this.y - this.py) * friction + this.vy * delta;
 
    this.px = this.x;
    this.py = this.y;
 
    this.x = nx;
    this.y = ny;
 
    this.vy = this.vx = 0;
 
    if (this.x >= w) {
      this.px = w + (w - this.px) * bounce;
      this.x = w;
    } else if (this.x <= 0) {
      this.px *= -1 * bounce;
      this.x = 0;
    }
 
    if (this.y >= h) {
      this.py = h + (h - this.py) * bounce;
      this.y = h;
    } else if (this.y <= 0) {
      this.py *= -1 * bounce;
      this.y = 0;
    }
 
    return this;
  }
 
  draw() {
    let i = this.constraints.length;
    while (i--) this.constraints[i].draw();
  }
 
  resolve() {
    if (this.pinX && this.pinY) {
      this.x = this.pinX;
      this.y = this.pinY;
      return;
    }
 
    this.constraints.forEach(constraint => constraint.resolve());
  }
 
  attach(point) {
    this.constraints.push(new Constraint(this, point));
  }
 
  free(constraint) {
    this.constraints.splice(this.constraints.indexOf(constraint), 1);
  }
 
  addForce(x, y) {
    this.vx += x;
    this.vy += y;
  }
 
  pin(pinx, piny) {
    this.pinX = pinx;
    this.pinY = piny;
  }
}
 
class Constraint {
  constructor(p1, p2) {
    this.p1 = p1;
    this.p2 = p2;
    this.length = spacing;
  }
 
  resolve() {
    let dx = this.p1.x - this.p2.x;
    let dy = this.p1.y - this.p2.y;
    let dist = Math.sqrt(dx * dx + dy * dy);
 
    if (dist < this.length) return;
 
    let diff = (this.length - dist) / dist;
 
    if (dist > tearDist) this.p1.free(this);
 
    let mul = diff * 0.5 * (1 - this.length / dist);
 
    let px = dx * mul;
    let py = dy * mul;
 
    !this.p1.pinX && (this.p1.x += px);
    !this.p1.pinY && (this.p1.y += py);
    !this.p2.pinX && (this.p2.x -= px);
    !this.p2.pinY && (this.p2.y -= py);
 
    return this;
  }
 
  draw() {
    ctx.moveTo(this.p1.x, this.p1.y);
    ctx.lineTo(this.p2.x, this.p2.y);
  }
}
 
class Cloth {
  constructor(free) {
    this.points = [];
 
    let startX = w / 2 - clothX * spacing / 2;
 
    for (let y = 0; y <= clothY; y++) {
      for (let x = 0; x <= clothX; x++) {
        let point = new Point(startX + x * spacing, 20 + y * spacing);
        !free && y === 0 && point.pin(point.x, point.y);
        x !== 0 && point.attach(this.points[this.points.length - 1]);
        y !== 0 && point.attach(this.points[x + (y - 1) * (clothX + 1)]);
 
        this.points.push(point);
      }
    }
  }
 
  update(delta) {
    let i = accuracy;
 
    while (i--) {
      this.points.forEach(point => {
        point.resolve();
      });
    }
 
    ctx.beginPath();
    this.points.forEach(point => {
      point.update(delta * delta).draw();
    });
    ctx.stroke();
  }
}
 
dragTracker({
  container: canvas,
  callbackDragStart: (_, pos) => {
    mouse.down = true;
    mouse.px = mouse.x = pos[0];
    mouse.py = mouse.y = pos[1];
  },
  callback: (_, pos) => {
    mouse.px = mouse.x;
    mouse.py = mouse.y;
    mouse.x = pos[0];
    mouse.y = pos[1];
  },
  callbackDragEnd: () => {
    mouse.down = false;
  },
});
 
 
let cloth = new Cloth();
 
//Animation loop
(function update(time) {
  ctx.clearRect(0, 0, w, h);
  cloth.update(0.016);
 
  requestAnimationFrame(update);
})();
 
 
let _g;
function zeroG() {
  if(gravity) {
    _g = gravity;
    gravity = 0;
  }
  else {
    gravity = _g;
  }
}
function setMode(pull) {
  modePull = pull;
}
function reset() {
  cloth = new Cloth(!gravity);
}
 
 
 
 
 
// window.requestAnimFrame =
//   window.requestAnimationFrame ||
//   window.webkitRequestAnimationFrame ||
//   window.mozRequestAnimationFrame ||
//   window.oRequestAnimationFrame ||
//   window.msRequestAnimationFrame ||
//   function (callback) {
//     window.setTimeout(callback, 1e3 / 60)
//   }
 
// let accuracy = 5
// let gravity = 400
// let clothY = 24
// let clothX = 50
// let spacing = 8
// let tearDist = 60
// let friction = 0.99
// let bounce = 0.5
 
// let canvas = document.getElementById('canvas')
// let ctx = canvas.getContext('2d')
 
// canvas.width = Math.min(700, window.innerWidth)
// canvas.height = 400
 
// ctx.strokeStyle = '#555'
 
// let mouse = {
//   cut: 8,
//   influence: 36,
//   down: false,
//   button: 1,
//   x: 0,
//   y: 0,
//   px: 0,
//   py: 0
// }
 
// class Point {
//   constructor (x, y) {
//     this.x = x
//     this.y = y
//     this.px = x
//     this.py = y
//     this.vx = 0
//     this.vy = 0
//     this.pinX = null
//     this.pinY = null
 
//     this.constraints = []
//   }
 
//   update (delta) {
//     if (this.pinX && this.pinY) return this
 
//     if (mouse.down) {
//       let dx = this.x - mouse.x
//       let dy = this.y - mouse.y
//       let dist = Math.sqrt(dx * dx + dy * dy)
 
//       if (mouse.button === 1 && dist < mouse.influence) {
//         this.px = this.x - (mouse.x - mouse.px)
//         this.py = this.y - (mouse.y - mouse.py)
//       } else if (dist < mouse.cut) {
//         this.constraints = []
//       }
//     }
 
//     this.addForce(0, gravity)
 
//     let nx = this.x + (this.x - this.px) * friction + this.vx * delta
//     let ny = this.y + (this.y - this.py) * friction + this.vy * delta
 
//     this.px = this.x
//     this.py = this.y
 
//     this.x = nx
//     this.y = ny
 
//     this.vy = this.vx = 0
 
//     if (this.x >= canvas.width) {
//       this.px = canvas.width + (canvas.width - this.px) * bounce
//       this.x = canvas.width
//     } else if (this.x <= 0) {
//       this.px *= -1 * bounce
//       this.x = 0
//     }
 
//     if (this.y >= canvas.height) {
//       this.py = canvas.height + (canvas.height - this.py) * bounce
//       this.y = canvas.height
//     } else if (this.y <= 0) {
//       this.py *= -1 * bounce
//       this.y = 0
//     }
 
//     return this
//   }
 
//   draw () {
//     let i = this.constraints.length
//     while (i--) this.constraints[i].draw()
//   }
 
//   resolve () {
//     if (this.pinX && this.pinY) {
//       this.x = this.pinX
//       this.y = this.pinY
//       return
//     }
 
//     this.constraints.forEach((constraint) => constraint.resolve())
//   }
 
//   attach (point) {
//     this.constraints.push(new Constraint(this, point))
//   }
 
//   free (constraint) {
//     this.constraints.splice(this.constraints.indexOf(constraint), 1)
//   }
 
//   addForce (x, y) {
//     this.vx += x
//     this.vy += y
//   }
 
//   pin (pinx, piny) {
//     this.pinX = pinx
//     this.pinY = piny
//   }
// }
 
// class Constraint {
//   constructor (p1, p2) {
//     this.p1 = p1
//     this.p2 = p2
//     this.length = spacing
//   }
 
//   resolve () {
//     let dx = this.p1.x - this.p2.x
//     let dy = this.p1.y - this.p2.y
//     let dist = Math.sqrt(dx * dx + dy * dy)
 
//     if (dist < this.length) return
 
//     let diff = (this.length - dist) / dist
 
//     if (dist > tearDist) this.p1.free(this)
 
//     let mul = diff * 0.5 * (1 - this.length / dist)
 
//     let px = dx * mul
//     let py = dy * mul
 
//     !this.p1.pinX && (this.p1.x += px)
//     !this.p1.pinY && (this.p1.y += py)
//     !this.p2.pinX && (this.p2.x -= px)
//     !this.p2.pinY && (this.p2.y -= py)
 
//     return this
//   }
 
//   draw () {
//     ctx.moveTo(this.p1.x, this.p1.y)
//     ctx.lineTo(this.p2.x, this.p2.y)
//   }
// }
 
// class Cloth {
//   constructor (free) {
//     this.points = []
 
//     let startX = canvas.width / 2 - clothX * spacing / 2
 
//     for (let y = 0; y <= clothY; y++) {
//       for (let x = 0; x <= clothX; x++) {
//         let point = new Point(startX + x * spacing, 20 + y * spacing)
//         !free && y === 0 && point.pin(point.x, point.y)
//         x !== 0 && point.attach(this.points[this.points.length - 1])
//         y !== 0 && point.attach(this.points[x + (y - 1) * (clothX + 1)])
 
//         this.points.push(point)
//       }
//     }
//   }
 
//   update (delta) {
//     let i = accuracy
 
//     while (i--) {
//       this.points.forEach((point) => {
//         point.resolve()
//       })
//     }
 
//     ctx.beginPath()
//     this.points.forEach((point) => {
//       point.update(delta * delta).draw()
//     })
//     ctx.stroke()
//   }
// }
 
// function setMouse (e) {
//   let rect = canvas.getBoundingClientRect()
//   mouse.px = mouse.x
//   mouse.py = mouse.y
//   mouse.x = e.clientX - rect.left
//   mouse.y = e.clientY - rect.top
// }
 
// canvas.onmousedown = (e) => {
//   mouse.button = e.which
//   mouse.down = true
//   setMouse(e)
// }
 
// canvas.onmousemove = setMouse
 
// canvas.onmouseup = () => (mouse.down = false)
 
// canvas.oncontextmenu = (e) => e.preventDefault()
 
// let cloth = new Cloth()
 
// function zeroG() {
//   gravity = 0
//   cloth = new Cloth(true)
// }
 
// ;(function update (time) {
//   ctx.clearRect(0, 0, canvas.width, canvas.height)
 
//   cloth.update(0.016)
 
//   window.requestAnimFrame(update)
// })(0)

<head>
<link href="style.scss" rel="stylesheet" type="text/css">
</head>
<body>
 
<canvas id="canvas"></canvas>
 
<div>
  <label><input type="radio" name="dragmode" onchange="setMode(true)" checked /> Pull</label>
  <label><input type="radio" name="dragmode" onchange="setMode(false)" /> Cut</label>
  <label><input type="checkbox" onchange="zeroG()" /> Zero G</label>
  <p>
    <button onclick="reset()">Reset</button>
    <!--button onclick="zeroG()">Zero G!</button-->
  </p>
</div>
 
<script type="text/javascript" src="drag-tracker.js"></script>
 
<script type="text/javascript" src="Cloth.js"></script>
 
</body>