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HTML

              
                <main>
  <svg id="svg">
    <g id="ribbon-layer"></g>
    <g>
      <polyline id="pencil-line" points="" />
      <rect id="pencil-point" width="1" height="1" />
    </g>
  </svg>

  <section id="hud">
    <h2 class="headline">Start Drawing!!!</h2>
    
    <div id="angle-range" class="range control layout-row">    
      <div class="range-label">
        Angle
      </div>
      <div class="flex">
        <input class="range-input" type="range" min="0" max="360" step="2" value="0" />
      </div>
      <div class="range-value">0</div>
    </div>
    
    <div id="width-range" class="range control layout-row">    
      <div class="range-label">
        Width
      </div>
      <div class="flex">
        <input class="range-input" type="range" min="1" max="80" step="1" value="80" />
      </div>
      <div class="range-value">0</div>
    </div>
    
    <div class="control">
      <button id="clear">Clear</button>
    </div>
  </section>
</main>
              
            
!

CSS

              
                body {
  background: #000;
  color: #dadada;
}

main {
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  visibility: hidden;
  opacity: 0;
}

button {
  color: black;
}

#svg {
  position: relative;
  width: 100%;
  height: 100%;  
  top: 0;
  left: 0;
} 

#hud {
  position: absolute;
  top: 0;
  left: 0;
  width: 300px;
  padding: 4px;  
  border: 1px solid #111;
  background: rgba(0,0,0,0.4);  
}

#pencil-line {
  fill: none;
  stroke: #ccc;
  stroke-width: 1;
  stroke-opacity: 0.8; 
}

#pencil-point {
  opacity: 0;
}

#ribbon-layer {
  pointer-events: none;
}

.headline {
  font-size: 18px;
  font-weight: normal;
  margin: 10px;
}

.ribbon {
  fill: none;
  stroke-linecap: round;  
  stroke-width: 2;
}

.control {
  padding: 10px;
}

.range {
  font-size: 14px;
  visibility: hidden;
  opacity: 0;
}

.range-label {
  min-width: 65px;
  width: 65px;
}

.range-value {
  min-width: 50px;
  width: 50px;  
  padding-left: 10px;
}

.range-input {
  width: 100%;
  vertical-align: middle;
}

.flex {
  box-sizing: border-box;
  flex: 1;
}

.layout-row {
  flex-direction: row;
}

.layout-column {
  flex-direction: column;
}


              
            
!

JS

              
                // Based on Israel Eisenberg's variable stroke width articles
// http://owl3d.com/svg/vsw/articles/

// Path simplification based on Simplify.js
// https://mourner.github.io/simplify-js/

//
// CATMULL ROM
// ========================================================================
namespace catmullRom {
  
  function getDistSq(p1x, p1y, p2x, p2y) {
    var dx = p1x - p2x;
    var dy = p1y - p2y;
    return dx * dx + dy * dy;
  }

  function getSegDistSq(px, py, p1x, p1y, p2x, p2y) {

    var x  = p1x;
    var y  = p1y;
    var dx = p2x - x;
    var dy = p2y - y;

    if (dx !== 0 || dy !== 0) {

      var t = ((px - x) * dx + (py - y) * dy) / (dx * dx + dy * dy);

      if (t > 1) {
        x = p2x;
        y = p2y;

      } else if (t > 0) {
        x += dx * t;
        y += dy * t;
      }
    }

    dx = px - x;
    dy = py - y;

    return dx * dx + dy * dy;
  }
  
  function simplifyRadialDist(points, toleranceSq) {
  
    var prevPointX = points[0];
    var prevPointY = points[1];
    var newPoints  = [prevPointX, prevPointY];
    var pointX, pointY;

    for (var i = 2, len = points.length; i < len; i += 2) {
      pointX = points[i];
      pointY = points[i+1];

      if (getDistSq(pointX, pointY, prevPointX, prevPointY) > toleranceSq) {
        newPoints.push(pointX, pointY);
        prevPointX = pointX;
        prevPointY = pointY;
      }
    }

    if (prevPointX !== pointX && prevPointY !== pointY) {
      newPoints.push(pointX, pointY);
    }

    return newPoints;
  }
  
  function simplifyDPStep(points, first, last, toleranceSq, simplified) {
    var maxDistSq = toleranceSq;
    var index;

    for (var i = first + 2; i < last; i += 2) {
      var distSq = getSegDistSq(
        points[i],     
        points[i+1], 
        points[first], 
        points[first+1], 
        points[last],  
        points[last+1]);

      if (distSq > maxDistSq) {
        index = i;
        maxDistSq = distSq;
      }
    }

    if (maxDistSq > toleranceSq) {
      if (index - first > 1) simplifyDPStep(points, first, index, toleranceSq, simplified);
      simplified.push(points[index], points[index+1]);
      if (last - index > 1) simplifyDPStep(points, index, last, toleranceSq, simplified);
    }
  }
  
  function simplifyDouglasPeucker(points, sqTolerance) {
  
    var last = points.length - 2;

    var simplified = [points[0], points[1]];

    simplifyDPStep(points, 0, last, sqTolerance, simplified);
    simplified.push(points[last], points[last + 1]);

    return simplified;
  }
  
  export function solve(points, tolerance = 1, highQuality = false, interpolate = false, k) {
        
    var size = points.length;
    
    if (size < 5) return;
    
    var toleranceSq = tolerance ** 2;
    points = highQuality ? points : simplifyRadialDist(points, toleranceSq);
    points = simplifyDouglasPeucker(points, toleranceSq);
        
    size = points.length;
    
    if (size < 3) return;
    if (size < 4) {      
      var sameX = (points[0] === points[2]);
      var sameY = (points[1] === points[3]);
      
      if (sameX && sameY) return;
    }
    
    if (k == null) k = 1;
  
    var last = size - 4;    
    var path = `M${points[0]},${points[1]}`;

    for (var i = 0; i < size - 2; i +=2) {

      var x0 = i ? points[i - 2] : points[0];
      var y0 = i ? points[i - 1] : points[1];

      var x1 = points[i + 0];
      var y1 = points[i + 1];

      var x2 = points[i + 2];
      var y2 = points[i + 3];

      var x3 = i !== last ? points[i + 4] : x2;
      var y3 = i !== last ? points[i + 5] : y2;

      if (interpolate) {
                
        var xc1 = (x0 + x1) / 2;
        var yc1 = (y0 + y1) / 2;
        var xc2 = (x1 + x2) / 2;
        var yc2 = (y1 + y2) / 2;
        var xc3 = (x2 + x3) / 2;
        var yc3 = (y2 + y3) / 2;

        var len1 = Math.sqrt((x1 - x0) * (x1 - x0) + (y1 - y0) * (y1 - y0));
        var len2 = Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
        var len3 = Math.sqrt((x3 - x2) * (x3 - x2) + (y3 - y2) * (y3 - y2));

        var k1 = len1 / (len1 + len2);
        var k2 = len2 / (len2 + len3);

        var xm1 = xc1 + (xc2 - xc1) * k1;
        var ym1 = yc1 + (yc2 - yc1) * k1;

        var xm2 = xc2 + (xc3 - xc2) * k2;
        var ym2 = yc2 + (yc3 - yc2) * k2;

        var cp1x = xm1 + (xc2 - xm1) * k + x1 - xm1;
        var cp1y = ym1 + (yc2 - ym1) * k + y1 - ym1;

        var cp2x = xm2 + (xc2 - xm2) * k + x2 - xm2;
        var cp2y = ym2 + (yc2 - ym2) * k + y2 - ym2;
        
      } else {
        
        var cp1x = x1 + (x2 - x0) / 6 * k;
        var cp1y = y1 + (y2 - y0) / 6 * k;

        var cp2x = x2 - (x3 - x1) / 6 * k;
        var cp2y = y2 - (y3 - y1) / 6 * k;        
      }

      path += ` C${cp1x},${cp1y},${cp2x},${cp2y},${x2},${y2}`;
    } 

    return path;
  }
}

//
// RIBBON PATH
// ========================================================================
class RibbonPath {
     
  group = document.querySelector("#layer-" + index);
  
  element = createSvg("path", {
    appendTo: this.group,
    class: "ribbon",
    d: ribbon.d
  });

  constructor(public ribbon, public index) {    
    this.update();
  }
  
  destroy() { 
    this.group.removeChild(this.element); 
  }

  update() {
    
    var ribbon    = this.ribbon;
    var progress  = this.index / ribbon.width;
    var transform = lerpArray(progress, ribbon.start, ribbon.end);
    var color     = lerpColor(progress, ribbon.color);
    var stroke    = `rgb(${color[0] >> 0},${color[1] >> 0},${color[2] >> 0})`;
    
    TweenLite.set(this.element, {
      x: transform[0],
      y: transform[1],
      stroke
    });
  }  
}

//
// RIBBON
// ========================================================================
class Ribbon {
  
  _angle = 0;
  _width = 0;

  color = colors.slice(0);
  dirty = false;

  paths = [];
  start = [];
  end   = [];
  
  constructor(public d, angle, width) {    
    this.update(angle, width);
  }

  get angle() { return this._angle; }
  set angle(n) {
    if (n != null && n !== this._angle) {
      this.dirty = true;
      this._angle = n;
    }    
  }

  get width() { return this._width }
  set width(n) {
    if (n != null && n !== this._width) {
      this.dirty = true;
      this._width = n;
    }    
  }

  destroy() {    
    _.forEach(this.paths, path => path.destroy());
  }

  update(angle, width) {
    
    this.angle = angle;
    this.width = width;
    
    if (!this.dirty) return;
        
    if (this.paths.length > this.width) {
      
      var paths = this.paths.splice(this.width);
      
      _.forEach(paths, path => path.destroy());
    }
          
    var x = (cos(180 - this.angle) * this.width / 2); 
    var y = (sin(180 - this.angle) * this.width / 2);

    this.start[0] =  x;
    this.start[1] = -y;
    this.end[0]   = -x;
    this.end[1]   =  y;
    
    for (var i = 0; i < this.width; i++) {
      
      var path = this.paths[i];
      
      if (path) {
        path.update();        
      } else {        
        this.paths[i] = new RibbonPath(this, i, this.width);
      }
    }    
    
    this.dirty = false;
  }
}

//
// PENCIL
// ========================================================================
class Pencil {
    
  points = [];

  lastX = 0;
  lastY = 0;

  line  = document.querySelector("#pencil-line");
  point = document.querySelector("#pencil-point");

  pencil = new Draggable(this.point, {
    bounds: "#svg",
    trigger: "#svg",
    cursor: "crosshair",
    onPress: this.onPress,
    onDrag: this.onDrag,
    onDragEnd: this.onDragEnd,
    callbackScope: this
  });
  
  constructor(public tolerance, public distSq) {
    
  }

  onPress(event) {
    
    render();
    
    var x = this.lastX = this.pencil.pointerX;
    var y = this.lastY = this.pencil.pointerY;
    
    TweenLite.set(this.point, { x, y });
    this.pencil.update();
    
    this.points.length = 0;      
    this.points.push(x, y);
  }

  onDrag(event) {
    
    var x = this.pencil.x;
    var y = this.pencil.y;
    
    var dx = (this.lastX - x) ** 2;
    var dy = (this.lastY - y) ** 2;
    
    if (dx + dy > this.distSq) {
      
      this.lastX = this.pencil.x;
      this.lastY = this.pencil.y;
      
      this.points.push(x, y);    
      this.line.setAttribute("points", this.points);
    }
  }

  onDragEnd(event) {
       
    var x = this.pencil.x;
    var y = this.pencil.y;
        
    this.points.push(x, y);
    
    if (this.points.length < 5) {
      this.points.push(x + 1, y + 1)
    }
       
    var path = catmullRom.solve(this.points, this.tolerance, false, false, 1);
    
    if (path) {
      
      var angle = angleRange.value;
      var width = widthRange.value;
      
      ribbons.push(new Ribbon(path, angle, width));
    }  
    
    this.points.length = 0;        
    this.line.setAttribute("points", "");
  }
}

//
// RANGE
// ========================================================================
class Range {
  
  dirty = false; 
  
  element = document.querySelector(selector);
  inputElement = this.element.querySelector(".range-input");
  valueElement = this.element.querySelector(".range-value");  

  constructor(selector, config) {
    
    this.inputElement.min   = config.min;
    this.inputElement.max   = config.max;
    this.inputElement.value = config.value;
    this.value = config.value;
    
    this.inputElement.addEventListener("input", event => {
      this.dirty = true;
      this.value = event.target.value;
    });
    
    TweenLite.set(this.element, { autoAlpha: 1 });
  }

  get value() { return this.inputElement.value; }
  set value(n) { this.valueElement.textContent = n; }
}

//
// RENDER
// ========================================================================
function render() {
  
  var angle = null;
  var width = null;
  
  if (angleRange.dirty) {
    angle = angleRange.value;
    angleRange.dirty = false;
  }
  
  if (widthRange.dirty) {
    width = widthRange.value;
    widthRange.dirty = false;
  }
  
  if (angle != null || width != null) {
    _.forEach(ribbons, ribbon => {      
      ribbon.update(angle, width);
    });
  }
}

//
// CREATE SVG
// ========================================================================
function createSvg(type, config) {
  var node = document.createElementNS(xmlns, type);
  
  if (config) {    
    if (config.appendTo) config.appendTo.appendChild(node);
    if (config.transforms) _.defaults(config, { x: "+=0" });    
    var attrs = "id,class,cx,cy,r,d,points".split(",");      
    var css   = _.assign(_.omit(config, attrs, "appendTo", "attr", "transforms"));
    css.attr  = _.assign(_.pick(config, attrs), _.omit(config.attr));
    TweenLite.set(node, css);
  }
  return node;
}

//
// HELPERS
// ========================================================================
function sin(deg) {
  return Math.sin(deg * rad);
}

function cos(deg) {
  return Math.cos(deg * rad);
}

function lerp(p, a, b) {
  return +a + (b - a) * p;
}

function lerpArray(p, a, b) {
  
  var c = [];
  
  for (var i = 0; i < a.length; i++) {
    c[i] = lerp(p, a[i], b[i]);
  }
  
  return c;
}

function lerpColor(p, color) {   
  if (p >= 1) return color[color.length - 1];
  p *= (color.length - 1);
  var i = p >> 0;
  return lerpArray(p - i, color[i], color[i + 1]);
}

//
// RUN
// ========================================================================
console.clear();

const xmlns = "http://www.w3.org/2000/svg";
const log   = console.log.bind(console);
const rad   = Math.PI / 180;

var angleConfig = {
  min: 0,
  max: 360,
  value: 70
};

var widthConfig = {
  min: 2,
  max: 40,
  value: 20
};

var renderFps = 1000 / 30;

var minDist = 10;
var tolerance = 10;

var colors  = [[0, 0, 128], [100, 192, 255]];
var ribbons = [];

var svg    = document.querySelector("#svg");
var clear  = document.querySelector("#clear");
var layers = document.querySelector("#ribbon-layer");

var angleRange = new Range("#angle-range", angleConfig);
var widthRange = new Range("#width-range", widthConfig);

_.times(widthConfig.max, i => {
  createSvg("g", {
    appendTo: layers,
    id: "layer-" + i
  });
});

var pencil = new Pencil(tolerance, minDist ** 2);

clear.addEventListener("click", event => {  
  _.forEach(ribbons, ribbon => ribbon.destroy());
  ribbons.length = 0;
});

TweenLite.ticker.addEventListener("tick", _.throttle(render, renderFps));
TweenLite.to("main", 0.5, { autoAlpha: 1 });









              
            
!
999px

Console