CanvasRenderingContext2D.shadowBlur

The CanvasRenderingContext2D.shadowBlur property of the Canvas 2D API specifies the level of the blurring effect; this value doesn't correspond to a number of pixels and is not affected by the current transformation matrix. The default value is 0.

Syntax

ctx.shadowBlur = level;

level

A float specifying the level of the blurring effect. The default value is 0. Negative, Infinity or NaN values are ignored.

Examples

Using the shadowBlur property

This is just a simple code snippet using the shadowblur property to set a blurred shadow. Note that shadows are only drawn, if the shadowColor property is set to a non-transparent value, too.

HTML

<canvas id="canvas"></canvas>

JavaScript

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
ctx.shadowColor = 'black';
ctx.shadowBlur = 10;
ctx.fillStyle = 'white';
ctx.fillRect(10, 10, 100, 100);

Edit the code below and see your changes update live in the canvas:

<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
ctx.shadowColor = 'black';
ctx.shadowBlur = 10;
ctx.fillStyle = 'white';
ctx.fillRect(10, 10, 100, 100);</textarea>

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var textarea = document.getElementById('code');
var reset = document.getElementById('reset');
var edit = document.getElementById('edit');
var code = textarea.value;
function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}
reset.addEventListener('click', function() {
  textarea.value = code;
  drawCanvas();
});
edit.addEventListener('click', function() {
  textarea.focus();
})
textarea.addEventListener('input', drawCanvas);
window.addEventListener('load', drawCanvas);

Specifications

Browser compatibility

WebKit/Blink-specific notes

• In WebKit- and Blink-based browsers, a non-standard and deprecated method ctx.setShadow() is implemented besides this property.

  setShadow(width, height, blur, color, alpha);
  setShadow(width, height, blur, graylevel, alpha);
  setShadow(width, height, blur, r, g, b, a);
  setShadow(width, height, blur, c, m, y, k, a);
  

See also

• The interface defining it, CanvasRenderingContext2D.