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<canvas id="c"></canvas>

<div id="new">
  Wobble some <a target="_blank" href="https://codepen.io/dissimulate/details/dJgMaO">jelly</a> <span class="bull">&bull;</span>
  Check out my <a target="_blank" href="https://www.instagram.com/abro_oks/">instagram!</a>
</div>

<div id="info">
  <div id="top">
    <a id="close" href="">&times;</a>
  </div>
  <p>
    <br>- Tear the cloth with your mouse.
    <br>
    <br>- Right click and drag to cut the cloth
    <br>
    <br>
    <br>
    <div class="center">
      <a id="github" target="_blank" href="https://github.com/suffick/Tearable-Cloth">GitHub</a>&nbsp;<span class="bull">&bull;</span>&nbsp;<a id="twitter" target="_blank" href="https://twitter.com/abro_oks">@abro_oks</a>
  </div>
    <br>
  </p>
</div>

document.getElementById('close').onmousedown = function(e) {
  e.preventDefault();
  document.getElementById('info').style.display = 'none';
  return false;
};

// settings

var physics_accuracy  = 3,
    mouse_influence   = 20,
    mouse_cut         = 5,
    gravity           = 1200,
    cloth_height      = 30,
    cloth_width       = 50,
    start_y           = 20,
    spacing           = 7,
    tear_distance     = 60;


window.requestAnimFrame =
    window.requestAnimationFrame ||
    window.webkitRequestAnimationFrame ||
    window.mozRequestAnimationFrame ||
    window.oRequestAnimationFrame ||
    window.msRequestAnimationFrame ||
    function (callback) {
        window.setTimeout(callback, 1000 / 60);
};

var canvas,
    ctx,
    cloth,
    boundsx,
    boundsy,
    mouse = {
        down: false,
        button: 1,
        x: 0,
        y: 0,
        px: 0,
        py: 0
    };

var Point = function (x, y) {
    this.x      = x;
    this.y      = y;
    this.px     = x;
    this.py     = y;
    this.vx     = 0;
    this.vy     = 0;
    this.pin_x  = null;
    this.pin_y  = null;
    
    this.constraints = [];
};

Point.prototype.update = function (delta) {
    if (mouse.down) {
        var diff_x = this.x - mouse.x,
            diff_y = this.y - mouse.y,
            dist = Math.sqrt(diff_x * diff_x + diff_y * diff_y);

        if (mouse.button == 1) {
            if (dist < mouse_influence) {
                this.px = this.x - (mouse.x - mouse.px) * 1.8;
                this.py = this.y - (mouse.y - mouse.py) * 1.8;
            }
          
        } else if (dist < mouse_cut) this.constraints = [];
    }

    this.add_force(0, gravity);

    delta *= delta;
    nx = this.x + ((this.x - this.px) * .99) + ((this.vx / 2) * delta);
    ny = this.y + ((this.y - this.py) * .99) + ((this.vy / 2) * delta);

    this.px = this.x;
    this.py = this.y;

    this.x = nx;
    this.y = ny;

    this.vy = this.vx = 0
};

Point.prototype.draw = function () {
    if (!this.constraints.length) return;

    var i = this.constraints.length;
    while (i--) this.constraints[i].draw();
};

Point.prototype.resolve_constraints = function () {
    if (this.pin_x != null && this.pin_y != null) {
        this.x = this.pin_x;
        this.y = this.pin_y;
        return;
    }

    var i = this.constraints.length;
    while (i--) this.constraints[i].resolve();

    this.x > boundsx ? this.x = 2 * boundsx - this.x : 1 > this.x && (this.x = 2 - this.x);
    this.y < 1 ? this.y = 2 - this.y : this.y > boundsy && (this.y = 2 * boundsy - this.y);
};

Point.prototype.attach = function (point) {
    this.constraints.push(
        new Constraint(this, point)
    );
};

Point.prototype.remove_constraint = function (constraint) {
    this.constraints.splice(this.constraints.indexOf(constraint), 1);
};

Point.prototype.add_force = function (x, y) {
    this.vx += x;
    this.vy += y;
  
    var round = 400;
    this.vx = ~~(this.vx * round) / round;
    this.vy = ~~(this.vy * round) / round;
};

Point.prototype.pin = function (pinx, piny) {
    this.pin_x = pinx;
    this.pin_y = piny;
};

var Constraint = function (p1, p2) {
    this.p1     = p1;
    this.p2     = p2;
    this.length = spacing;
};

Constraint.prototype.resolve = function () {
    var diff_x  = this.p1.x - this.p2.x,
        diff_y  = this.p1.y - this.p2.y,
        dist    = Math.sqrt(diff_x * diff_x + diff_y * diff_y),
        diff    = (this.length - dist) / dist;

    if (dist > tear_distance) this.p1.remove_constraint(this);

    var px = diff_x * diff * 0.5;
    var py = diff_y * diff * 0.5;

    this.p1.x += px;
    this.p1.y += py;
    this.p2.x -= px;
    this.p2.y -= py;
};

Constraint.prototype.draw = function () {
    ctx.moveTo(this.p1.x, this.p1.y);
    ctx.lineTo(this.p2.x, this.p2.y);
};

var Cloth = function () {
    this.points = [];

    var start_x = canvas.width / 2 - cloth_width * spacing / 2;

    for (var y = 0; y <= cloth_height; y++) {
        for (var x = 0; x <= cloth_width; x++) {
            var p = new Point(start_x + x * spacing, start_y + y * spacing);

            x != 0 && p.attach(this.points[this.points.length - 1]);
            y == 0 && p.pin(p.x, p.y);
            y != 0 && p.attach(this.points[x + (y - 1) * (cloth_width + 1)])

            this.points.push(p);
        }
    }
};

Cloth.prototype.update = function () {
    var i = physics_accuracy;

    while (i--) {
        var p = this.points.length;
        while (p--) this.points[p].resolve_constraints();
    }

    i = this.points.length;
    while (i--) this.points[i].update(.016);
};

Cloth.prototype.draw = function () {
    ctx.beginPath();

    var i = cloth.points.length;
    while (i--) cloth.points[i].draw();

    ctx.stroke();
};

function update() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);

    cloth.update();
    cloth.draw();

    requestAnimFrame(update);
}

function start() {
    canvas.onmousedown = function (e) {
        mouse.button  = e.which;
        mouse.px      = mouse.x;
        mouse.py      = mouse.y;
        var rect      = canvas.getBoundingClientRect();
        mouse.x       = e.clientX - rect.left,
        mouse.y       = e.clientY - rect.top,
        mouse.down    = true;
        e.preventDefault();
    };

    canvas.onmouseup = function (e) {
        mouse.down = false;
        e.preventDefault();
    };

    canvas.onmousemove = function (e) {
        mouse.px  = mouse.x;
        mouse.py  = mouse.y;
        var rect  = canvas.getBoundingClientRect();
        mouse.x   = e.clientX - rect.left,
        mouse.y   = e.clientY - rect.top,
        e.preventDefault();
    };

    canvas.oncontextmenu = function (e) {
        e.preventDefault();
    };

    boundsx = canvas.width - 1;
    boundsy = canvas.height - 1;

    ctx.strokeStyle = '#888';
  
    cloth = new Cloth();
  
    update();
}

window.onload = function () {
    canvas  = document.getElementById('c');
    ctx     = canvas.getContext('2d');

    canvas.width  = 560;
    canvas.height = 350;

    start();
};

* {
    margin: 0;
    overflow: hidden;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    -o-user-select: none;
    user-select: none;
}
body {
    background: #F2F2F2;
}
#c {
    display: block;
    margin: 20px auto 0;
}
#info {
    position: absolute;
    left: -1px;
    top: -1px;
    width: auto;
    max-width: 420px;
    height: auto;
    background: #f8f8f8;
    border-bottom-right-radius: 10px;
    border:1px solid #ccc;
}
#top {
    background: #fff;
    width: 100%;
    height: auto;
    position: relative;
    border-bottom: 1px solid #eee;
}
p {
    font-family: Arial, sans-serif;
    color: #666;
    text-align: justify;
    font-size: 16px;
    margin: 0px 16px;
}
#github, #twitter {
  color:#3377ee;
  font-family: Helvetica, Arial, sans-serif;
  font-size: 14px;
  margin: 0 auto;
  text-align: center;
  text-decoration:none;
}
.center {
  text-align: center;
}
#net {
  text-align:center;
  white-space:nowrap;
  font-size:19px;
  background:rgba(0,0,0,0.1);
  padding:8px 12px;
  border-radius:8px;
  display:block;
  color:#888;
}
#net > span {
  color:#3377ee;
  font-family: Helvetica, Arial, sans-serif;
  font-size: 14px;
  display: block;
  margin: 0 auto;
  text-align: center;
  text-decoration:none;
}
a {
    font-family: sans-serif;
    color: #444;
    text-decoration: none;
    font-size: 20px;
}
#site {
    float: left;
    margin: 10px;
    color: #ff9900;
  border-bottom: 1px dashed #ccc;
  padding-bottom:3px
}
#site:hover {
    color: #ffaa11;
}
#close {
    float: right;
    margin: 10px;
}
#p {
    font-family: Verdana, sans-serif;
    position: absolute;
    right: 10px;
    bottom: 10px;
    color: #4099ff;
    border: 1px dashed #4099ff;
    padding: 4px 8px;
}

#new {
  width: 100%;
  text-align: center;
  font-size: 18px;
  font-family: Helvetica;
  margin-top: 12px;
}

#new a {
  font-size: 20px;
  color: #4099ff;
}

.bull {
  opacity: 0.3;
  margin: 0 6px;
  font-size: 14px;
}