Info

How much faster is it to render just the parts of the canvas that changed, compared to the whole thing?

Rendering a white dot that moves across a black background.

Preparation code

<canvas id="c" width="640" height="480"></canvas>
<script>
  var canvas = document.getElementById('c');
  var context = canvas.getContext('2d');
  
  var HEIGHT = 100;
</script>

Preparation code output

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for (var i = 0; i < canvas.width; i++) {
  context.fillStyle = '#000';
  context.fillRect(0, 0, canvas.width, canvas.height);
  context.fillStyle = '#fff';
  context.fillRect(i, HEIGHT, 1, 1);
}

for (var i = 0; i < canvas.width; i++) {
  //context.fillStyle = 'black';
  context.clearRect(i-1, HEIGHT, 1, 1);
  context.fillStyle = 'white';
  context.fillRect(i, HEIGHT, 1, 1);
}

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Revisions

You can edit these tests or add even more tests to this page by appending /edit to the URL. Here’s a list of current revisions for this page:

• Revision 1: published by Boris on 1st August 2011 and last updated on 2nd August 2011
• Revision 2: published by Boris on 13th August 2011
• Revision 7: published on 18th July 2012
• Revision 8: published on 18th July 2012
• Revision 9: published on 22nd July 2012
• Revision 10: published on 16th August 2012
• Revision 11: published on 11th November 2012
• Revision 12: published on 3rd March 2013
• Revision 13: published on 3rd March 2013

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