CanvasRenderingContext2D.shadowBlur - Web APIs 编辑

The CanvasRenderingContext2D.shadowBlur property of the Canvas 2D API specifies the amount of blur applied to shadows. The default is 0 (no blur).

Note: Shadows are only drawn if the shadowColor property is set to a non-transparent value. One of the shadowBlur, shadowOffsetX, or shadowOffsetY properties must be non-zero, as well.

Syntax

ctx.shadowBlur = level;

level

A non-negative float specifying the level of shadow blur, where 0 represents no blur and larger numbers represent increasingly more blur. This value doesn't correspond to a number of pixels, and is not affected by the current transformation matrix. The default value is 0. Negative, Infinity, and NaN values are ignored.

Examples

Adding a shadow to a shape

This example adds a blurred shadow to a rectangle. The shadowColor property sets its color, and shadowBlur sets its level of bluriness.

HTML

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

JavaScript

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

// Shadow
ctx.shadowColor = 'red';
ctx.shadowBlur = 15;

// Rectangle
ctx.fillStyle = 'blue';
ctx.fillRect(20, 20, 150, 100);

Result

Specifications

Browser compatibility

BCD tables only load in the browser

WebKit/Blink-specific notes

In WebKit- and Blink-based browsers, the 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 this property: CanvasRenderingContext2D
• CanvasRenderingContext2D.shadowColor