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HTML5 Canvas - Rotation


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HTML5 canvas provides rotate(angle) method which is used to rotate the canvas around the current origin.

This method only takes one parameter and that's the angle the canvas is rotated by. This is a clockwise rotation measured in radians.

Example:

Following is a simple example which we are running two loops where first loop determines the number of rings, and the second determines the number of dots drawn in each ring.

<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript">
function drawShape(){
  // get the canvas element using the DOM
  var canvas = document.getElementById('mycanvas');
  // Make sure we don't execute when canvas isn't supported
  if (canvas.getContext){
    // use getContext to use the canvas for drawing
    var ctx = canvas.getContext('2d');
    ctx.translate(100,100);
    for (i=1; i<7; i++){
       ctx.save();
       ctx.fillStyle = 'rgb('+(51*i)+','+(200-51*i)+',0)';
       for (j=0; j < i*6; j++){
          ctx.rotate(Math.PI*2/(i*6));
          ctx.beginPath();
          ctx.arc(0,i*12.5,5,0,Math.PI*2,true);
          ctx.fill();
       }
       ctx.restore();
     }
  }else {
    alert('You need Safari or Firefox 1.5+ to see this demo.');
  }
}
</script>
</head>
<body onload="drawShape();">
   <canvas id="mycanvas" width="400" height="400"></canvas>
</body>
</html>

The above example would produce following result:

Canvas Rotation

To learn above concept - Do Online Practice using latest version of either Safari or Opera.



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