CanvasRenderingContext2D.shadowColor - Web APIs 编辑

The CanvasRenderingContext2D.shadowColor property of the Canvas 2D API specifies the color of shadows.

Be aware that the shadow's rendered opacity will be affected by the opacity of the fillStyle color when filling, and of the strokeStyle color when stroking.

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.shadowColor = color;

color

A DOMString parsed as a CSS <color> value. The default value is fully-transparent black.

Examples

Adding a shadow to shapes

This example adds a shadow to two squares; the first one is filled, and the second one is stroked. The shadowColor property sets the shadows' color, while shadowOffsetX and shadowOffsetY set their position relative to the shapes.

HTML

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

JavaScript

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

// Shadow
ctx.shadowColor = 'red';
ctx.shadowOffsetX = 10;
ctx.shadowOffsetY = 10;

// Filled rectangle
ctx.fillRect(20, 20, 100, 100);

// Stroked rectangle
ctx.lineWidth = 6;
ctx.strokeRect(170, 20, 100, 100);

Result

Shadows on translucent shapes

A shadow's opacity is affected by the transparency level of its parent object (even when shadowColor specifies a completely opaque value). This example strokes and fills a rectangle with translucent colors.

HTML

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

JavaScript

The resulting alpha value of the fill shadow is .8 * .2, or .16. The alpha of the stroke shadow is .8 * .6, or .48.

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

// Shadow
ctx.shadowColor = 'rgba(255, 0, 0, .8)';
ctx.shadowBlur = 8;
ctx.shadowOffsetX = 30;
ctx.shadowOffsetY = 20;

// Filled rectangle
ctx.fillStyle = 'rgba(0, 255, 0, .2)';
ctx.fillRect(10, 10, 150, 100);

// Stroked rectangle
ctx.lineWidth = 10;
ctx.strokeStyle = 'rgba(0, 0, 255, .6)';
ctx.strokeRect(10, 10, 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