canvas

by chris richarde

HTML

<button onclick="doDrawing();">Start Drawing</button>
<button onclick="stopDrawing();">Stop Drawing</button>
<canvas id="myCanvas" width="500" height="500" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>

JavaScript

var t = 0;
var c = document.getElementById("myCanvas");
var R = 0;
var r =0;
var O = 0;
var ctx = c.getContext("2d");
var s = c.width / 2;


function doDrawing() {
    t = 0;
    O = Math.floor((Math.random() * 30) + 25);
    r = Math.floor((Math.random() * 30) + 25);
    R = Math.floor((Math.random() * 50) + 25);

     
    // Clear the Canvas
    ctx.clear();
    
    // Create a random color
    var timesRun = 0;
    var color =  '#'+Math.floor(Math.random()*16777215).toString(16);
    
    // Initial x and y
    var x = (s + (R + r) * Math.cos(t) - (r + O) * Math.cos(((R + r) / r) * t));
    var y =  (s + (R + r) * Math.sin(t) - (r + O) * Math.sin(((R + r) / r) * t));

    // Start the Drawing
    ctx.beginPath();
    ctx.strokeStyle = color;
    ctx.moveTo(x,y);
      
    //Use the timer to create drawing
    var interval = setInterval(function(){
    timesRun += 1;
    if(timesRun === 1000){
        clearInterval(interval); }
        
    drawCircle();}, 20); 
    
}
function drawCircle()
{
  t += 0.1;
   var x = (s + (R + r) * Math.cos(t) - (r + O) * Math.cos(((R + r) / r) * t));
        var y = (s + (R + r) * Math.sin(t) - (r + O) * Math.sin(((R + r) / r) * t));

  ctx.lineTo(x,y);  
  ctx.stroke();
}

CanvasRenderingContext2D.prototype.clear = 
  CanvasRenderingContext2D.prototype.clear || function (preserveTransform) {
    if (preserveTransform) {
      this.save();
      this.setTransform(1, 0, 0, 1, 0, 0);
    }

    this.clearRect(0, 0, this.canvas.width, this.canvas.height);

    if (preserveTransform) {
      this.restore();
    }           
};