Question

197

How to draw a blurry circle on HTML5 canvas?

rated 0 times [ 198] [ 1] / answers: 1 / hits: 28412 / 13 Years ago, tue, march 29, 2011, 12:00:00

I'm able to draw a simple circle on HTML5 canvas, but I'd like to add some blur around it.

What I found was this website which explains the shadowBlur property which can come in handy here.

However, I cannot manage to make the circle itself blurry. What the shadowBlur property basically does is painting some blur effect after the regular circle has been drawn. What I've tried so far I've put on jsFiddle.

As can be seen, it's a solid filled circle with some blur effect around it - the two parts do not blend into each other at all. What I actually would like to achieve is that the circle itself is fully blurred like this:

blurred

Is there any way to draw a blurred circle like this, i.e. that the circle itself also has a blur effect?

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alvin

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3 Years ago

answered 13 Years ago mireyag · Accepted Answer

I'd strongly suggest against blur algorithms unless you are blurring some already-existing drawing that is complex.

For your case, just draw a rect with a radial gradient.

  var radgrad = ctx.createRadialGradient(60,60,0,60,60,60);

  radgrad.addColorStop(0, 'rgba(255,0,0,1)');

  radgrad.addColorStop(0.8, 'rgba(228,0,0,.9)');

  radgrad.addColorStop(1, 'rgba(228,0,0,0)');



  // draw shape

  ctx.fillStyle = radgrad;

  ctx.fillRect(0,0,150,150);

Example:

http://jsfiddle.net/r8Kqy/48/