Web/API/CanvasRenderingContext2D/lineDashOffset

The CanvasRenderingContext2D.lineDashOffset property of the Canvas 2D API sets the line dash offset, or "phase."

Note: Lines are drawn by calling the stroke() method.

Syntax

ctx.lineDashOffset = value;

value

A float specifying the amount of the line dash offset. The default value is 0.0.

Examples

Offsetting a line dash

This example draws two dashed lines. The first has no dash offset. The second has a dash offset of 4.

HTML

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

JavaScript

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

ctx.setLineDash([4, 16]);

// Dashed line with no offset
ctx.beginPath();
ctx.moveTo(0, 50);
ctx.lineTo(300, 50);
ctx.stroke();

// Dashed line with offset of 4
ctx.beginPath();
ctx.strokeStyle = 'red';
ctx.lineDashOffset = 4;
ctx.moveTo(0, 100);
ctx.lineTo(300, 100);
ctx.stroke();

Result

The line with a dash offset is drawn in red.

Marching ants

The marching ants effect is an animation technique often found in selection tools of computer graphics programs. It helps the user to distinguish the selection border from the image background by animating the border.

HTML

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

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
let offset = 0;

function draw() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.setLineDash([4, 2]);
  ctx.lineDashOffset = -offset;
  ctx.strokeRect(10, 10, 100, 100);
}

function march() {
  offset++;
  if (offset > 16) {
    offset = 0;
  }
  draw();
  setTimeout(march, 20);
}

march();

Specifications

Specification	Status	Comment
HTML Living StandardThe definition of 'CanvasRenderingContext2D.lineDashOffset' in that specification.	Living Standard

Browser compatibility

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
lineDashOffset	Chrome Full support Yes	Edge Full support 12	Firefox Full support 27 Full support 27 Full support 7 Alternate Name' Alternate Name' Uses the non-standard name: mozDashOffset	IE Full support 11	Opera Full support Yes	Safari Full support Yes	WebView Android Full support Yes	Chrome Android Full support Yes	Firefox Android Full support 27 Full support 27 Full support 7 Alternate Name' Alternate Name' Uses the non-standard name: mozDashOffset	Opera Android Full support Yes	Safari iOS Full support Yes	Samsung Internet Android Full support Yes

Legend

Full support  

Full support

Uses a non-standard name.'

Uses a non-standard name.

See also

• The interface defining this property: CanvasRenderingContext2D
• CanvasRenderingContext2D.getLineDash()
• CanvasRenderingContext2D.setLineDash()
• Applying styles and color

CanvasRenderingContext2D.lineDashOffset by Mozilla Contributors is licensed under CC-BY-SA 2.5.