Animate a Canvas circle to draw on load

Question 1

Animate a Canvas circle to draw on load

canvas jquery-animate draw radial

Blackline · Mar 28, 2013 · Viewed 31.4k times · Source

Answer

Answer

// requestAnimationFrame Shim
(function() {
  var requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame ||
                              window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
  window.requestAnimationFrame = requestAnimationFrame;
})();



var canvas = document.getElementById('myCanvas');
 var context = canvas.getContext('2d');
 var x = canvas.width / 2;
 var y = canvas.height / 2;
 var radius = 75;
 var endPercent = 85;
 var curPerc = 0;
 var counterClockwise = false;
 var circ = Math.PI * 2;
 var quart = Math.PI / 2;

 context.lineWidth = 10;
 context.strokeStyle = '#ad2323';
 context.shadowOffsetX = 0;
 context.shadowOffsetY = 0;
 context.shadowBlur = 10;
 context.shadowColor = '#656565';


 function animate(current) {
     context.clearRect(0, 0, canvas.width, canvas.height);
     context.beginPath();
     context.arc(x, y, radius, -(quart), ((circ) * current) - quart, false);
     context.stroke();
     curPerc++;
     if (curPerc < endPercent) {
         requestAnimationFrame(function () {
             animate(curPerc / 100)
         });
     }
 }

 animate();

Basically I used the same formula from the demo link you posted. I then added an animation function that when called will update the circle until it reaches the desired ending percent.

The animation is continually called by requestAnimationFrame this is the preferred way of doing any kind of animations with canvas. Every time animate is called the current percent is increased by one, which is then used to redraw the arc.

Question 2

OK Hello.

I've decided to start using HTML canvas for a small project I have.

There's no real start yet. I'm just learning the basics of Canvas and I want to Animate a circle

<!DOCTYPE html>
<html>
 <head>
  <meta charset="UTF-8">
  <title>title</title>
    <style>
      body {
        margin: 0px;
        padding: 0px;
        background: #222;
      }

     </style>
  <link rel="stylesheet" href="style.css" type="text/css">
 </head>
<body>
<canvas id="myCanvas" width="578" height="250"></canvas>

    <script>
      var canvas = document.getElementById('myCanvas');
      var context = canvas.getContext('2d');
      var x = canvas.width / 2;
      var y = canvas.height / 2;
      var radius = 75;
      var startAngle = 1.5 * Math.PI;
      var endAngle = 3.2 * Math.PI;
      var counterClockwise = false;
      context.beginPath();
      context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
      context.lineWidth = 15;
      // line color
      context.strokeStyle = 'black';
      context.stroke();
    </script>

  <script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js" type="text/javascript"></script>
  <script src="//ajax.googleapis.com/ajax/libs/mootools/1.4.5/mootools-yui-compressed.js" type="text/javascript"></script>
 </body>
</html>

Here is a fiddle http://jsfiddle.net/oskar/Aapn8/ of what I'm trying to achieve. I'm not to fussed with the "Bounce" effect.

But i basically want it to Draw on page load and stop at the desired Angle of the Arc Here's the Fiddle of what I've created so far.

http://jsfiddle.net/skerwin/uhVj6/

Thanks

Animate a Canvas circle to draw on load

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