A5 Canvas HTML

Testing out canvas

by scotp71

HTML

<canvas id="myCanvas" width="400" height="400" style="border: 1px solid black">Your browser does not support the HTML5 canvas tag.</canvas>
<div>
<button onclick="doDrawing();">Draw</button>
</div>

JavaScript

var t = 0;
var r = 0;
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var center = c.width/2;
var R = center/2;
var itr = 360;
var O = 45

function doDrawing() {
		
    t = 0;
    r = Math.random();
    // 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 = R+R*Math.cos(0);
    //var y = R+R*Math.sin(0);
    var x = (center+(R+r)*Math.cos(t) - (r+O)*Math.cos(((R+r)/r)*t));
    var y = (center+(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 === itr){
        clearInterval(interval); }
        
    drawSpiro();}, 20); 
    
}
function drawSpiro()
{
  t += 0.1;
  x = Math.floor(center+(R+r)*Math.cos(t) - (r+O)*Math.cos(((R+r)/r)*t));
  y = Math.floor(center+(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();
    }           
};