CanvasRenderingContext2D.createPattern() - Web APIs 编辑

The CanvasRenderingContext2D.createPattern() method of the Canvas 2D API creates a pattern using the specified image and repetition. This method returns a CanvasPattern.

This method doesn't draw anything to the canvas directly. The pattern it creates must be assigned to the CanvasRenderingContext2D.fillStyle or CanvasRenderingContext2D.strokeStyle properties, after which it is applied to any subsequent drawing.

Syntax

CanvasPattern ctx.createPattern(image, repetition);

Parameters

image

A CanvasImageSource to be used as the pattern's image. It can be any of the following:

• HTMLImageElement (<img>)
• SVGImageElement (<image>)
• HTMLVideoElement (<video>, by using the capture of the video)
• HTMLCanvasElement (<canvas>)
• ImageBitmap
• OffscreenCanvas

repetition

A DOMString indicating how to repeat the pattern's image. Possible values are:

• "repeat" (both directions)
• "repeat-x" (horizontal only)
• "repeat-y" (vertical only)
• "no-repeat" (neither direction)

If repetition is specified as an empty string ("") or null (but not undefined), a value of "repeat" will be used.

Return value

CanvasPattern

An opaque object describing a pattern.

Examples

Creating a pattern from an image

This example uses the createPattern() method to create a CanvasPattern with a repeating source image. Once created, the pattern is assigned to the canvas context's fill style and applied to a rectangle.

The original image looks like this:

HTML

<canvas id="canvas" width="300" height="300"></canvas>

JavaScript

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

var img = new Image();
img.src = 'https://mdn.mozillademos.org/files/222/Canvas_createpattern.png';
img.onload = function() {
  var pattern = ctx.createPattern(img, 'repeat');
  ctx.fillStyle = pattern;
  ctx.fillRect(0, 0, 300, 300);
};

Creating a pattern from a canvas

In this example we create a pattern from the contents of an offscreen canvas. We then apply it to the fill style of our primary canvas, and fill that canvas with the pattern.

JavaScript

// Create a pattern, offscreen
const patternCanvas = document.createElement('canvas');
const patternContext = patternCanvas.getContext('2d');

// Give the pattern a width and height of 50
patternCanvas.width = 50;
patternCanvas.height = 50;

// Give the pattern a background color and draw an arc
patternContext.fillStyle = '#fec';
patternContext.fillRect(0, 0, patternCanvas.width, patternCanvas.height);
patternContext.arc(0, 0, 50, 0, .5 * Math.PI);
patternContext.stroke();

// Create our primary canvas and fill it with the pattern
const canvas = document.createElement('canvas');
const ctx = canvas.getContext('2d');
const pattern = ctx.createPattern(patternCanvas, 'repeat');
ctx.fillStyle = pattern;
ctx.fillRect(0, 0, canvas.width, canvas.height);

// Add our primary canvas to the webpage
document.body.appendChild(canvas);

Result

Specifications

Browser compatibility

BCD tables only load in the browser

Gecko-specific notes

• Starting with Gecko 5.0 (Firefox 5.0 / Thunderbird 5.0 / SeaMonkey 2.2), specifying a null or undefined image correctly throws a TYPE_MISMATCH_ERR exception.
• Starting with Gecko 16.0 (Firefox 16.0 / Thunderbird 16.0 / SeaMonkey 2.13), specifying null for the repetition parameter is now allowed and results in the repetition being set to "repeat" (bug 762657).

See also

• The interface defining this method: CanvasRenderingContext2D
• CanvasPattern