CanvasRenderingContext2D.globalCompositeOperation - Web APIs 编辑

The CanvasRenderingContext2D.globalCompositeOperation property of the Canvas 2D API sets the type of compositing operation to apply when drawing new shapes.

See also Compositing and clipping in the Canvas Tutorial.

Syntax

ctx.globalCompositeOperation = type;

type is a String identifying which of the compositing or blending mode operations to use.

Examples

Changing the composite operation

This example uses the globalCompositeOperation property to draw two rectangles that exclude themselves where they overlap.

HTML

<canvas></canvas>

JavaScript

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

ctx.globalCompositeOperation = 'xor';

ctx.fillStyle = 'blue';
ctx.fillRect(10, 10, 100, 100);

ctx.fillStyle = 'red';
ctx.fillRect(50, 50, 100, 100);

Result

Specifications

Browser compatibility

BCD tables only load in the browser

WebKit/Blink-specific notes

• In WebKit- and Blink-based Browsers, a non-standard and deprecated method ctx.setCompositeOperation() is implemented besides this property.
• Support for "plus-darker" and "darker" were removed in Chrome 48. Developers looking for a replacement should use "darken".

Gecko-specific notes

• An early Canvas specification draft specified the value "darker". However, Firefox removed support for "darker" in version 4 (bug 571532). See also this blog post that suggests using "difference" as a way to achieve a similar affect to "darker".

See also

• The interface defining this property: CanvasRenderingContext2D
• CanvasRenderingContext2D.globalAlpha