How to draw a blurry circle on HTML5 canvas?

javascript html canvas geometry blur

25,346

Solution 1

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/

Solution 2

You may find the context.filter property useful

var canvas = document.getElementById('canvas');

var context = canvas.getContext('2d');

context.filter = "blur(16px)";

context.fillStyle = "#f00";
context.beginPath();
context.arc(100, 100, 50, 0, Math.PI * 2, true);
context.fill();

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
</head>

<body>
  <canvas width=200 height=200 id='canvas'></canvas>
</body>

</html>

Note as of April 2017, IE, Opera and Safari don't support this

Solution 3

You probably can obtain the bitmap pixel array and apply some blurring algorithm on top of it. For example: http://www.jhlabs.com/ip/blurring.html

Solution 4

You can draw a blurred circle with the following function:

function drawblurrycircle(context, x, y, radius, blur)
{
     context.shadowBlur = blur;
     context.shadowOffsetX = 0;
     context.shadowOffsetY = 0;

     context.fillStyle="#FF0000";
     context.shadowColor="#FF0000"; //set the shadow colour to that of the fill

     context.beginPath();
     context.arc(x,y,radius,0,Math.PI*2,true);
     context.fill();
     context.stroke();
}

View more solutions

25,346

Author by

pimvdb

Updated on July 09, 2022

Comments

pimvdb almost 2 years

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:

Is there any way to draw a blurred circle like this, i.e. that the circle itself also has a blur effect?
pimvdb about 13 years

Very interesting. However, as I'm using it a renderer (20fps) I guess it will become a little overcomplicated and slow... But I'll give it a shot, thanks.
Phrogz about 13 years

@pimvdb Blur it once to an offscreen canvas and then blit the result to your canvas using drawImage().
Phrogz about 13 years

Here's a better, very fast blur written for HTML5 Canvas: StackBlur
Phrogz about 13 years

+1 for using RGBA to get proper transparency in the blur region. Nice work.
pimvdb almost 12 years

I'm sorry but I already posted that I tried shadowBlur, and that the problem is that the shadow does not blend into the cicle. Your solution suffers from that very same issue, unfortunately. jsfiddle.net/r8Kqy/410
starbeamrainbowlabs almost 12 years

Sorry! I did not read your post thoroughly. To make it look better, you could use a for loop to blur it multiple times
Ivan Kuckir over 10 years

But remember, this is not a real (gaussian) blur! This blur is made by a "cone" with straight edge, real (gaussian) blur will look much softer. You can approximate it by adding more colorStops.
Graham Lea almost 5 years

Maybe it's because it's 6 years later, but the above JSFiddle doesn't seem to do anything.
sebastian.derossi almost 5 years

@GrahamLea Yikes! you're correct, have a looks at this jsfiddle.net/s0c9wndh Seems like BoxBlurFilter is no longer used in the latest version, use BlurFilter instead [code] var stage = new createjs.Stage("test"); var s = new createjs.Shape(); var g = s.graphics; g.f("#FF0000").dc(0, 0, 75); s.x = 100; s.y = 100; s.filters = [new createjs.BlurFilter(5, 5, 3)]; stage.addChild(s); s.cache(-100, -100, 200, 200); s.alpha = 0.5; stage.update(); [/code]
Niranth Reddy over 4 years

This is perfectly fine. But in my case, I need to work with imageData directly instead of context. Any way to add blur circle by modifying imageData directly ??
Crashalot almost 4 years

still unsupported on safari as of july 2020