CanvasRenderingContext2D.lineDashOffset
The CanvasRenderingContext2D
.lineDashOffset
property of the Canvas 2D API sets the line dash pattern offset or "phase" to achieve a "marching ants" effect, for example.
Syntax
<var>ctx.lineDashOffset = value;</var>
value
- A float specifying the amount of the offset. Initially
0.0
.
Examples
Using the lineDashOffset
property
This is just a simple code snippet which uses the lineDashOffset
property to draw a dashed line.
HTML
<canvas id="canvas"></canvas>
JavaScript
var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); ctx.setLineDash([4, 16]); ctx.lineDashOffset = 2; ctx.beginPath(); ctx.moveTo(0,100); ctx.lineTo(400, 100); ctx.stroke();
Edit the code below and see your changes update live in the canvas:
Playable code
<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas> <div class="playable-buttons"> <input id="edit" type="button" value="Edit" /> <input id="reset" type="button" value="Reset" /> </div> <textarea id="code" class="playable-code" style="height: 120px"> ctx.setLineDash([4, 16]); ctx.lineDashOffset = 2; ctx.beginPath(); ctx.moveTo(0,100); ctx.lineTo(400, 100); ctx.stroke();</textarea>
var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); var textarea = document.getElementById("code"); var reset = document.getElementById("reset"); var edit = document.getElementById("edit"); var code = textarea.value; function drawCanvas() { ctx.clearRect(0, 0, canvas.width, canvas.height); eval(textarea.value); } reset.addEventListener("click", function() { textarea.value = code; drawCanvas(); }); edit.addEventListener("click", function() { textarea.focus(); }) textarea.addEventListener("input", drawCanvas); window.addEventListener("load", drawCanvas);
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" class="playable-canvas"></canvas>
var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); var 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 |
---|---|---|
WHATWG HTML Living Standard The definition of 'CanvasRenderingContext2D.lineDashOffset' in that specification. |
Living Standard |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | 7 (7) mozDashOffset 27 (27) |
11 | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | 7 (7) mozDashOffset 27.0 (27) |
(Yes) | (Yes) | (Yes) |
Gecko-specific notes
- Starting with Gecko 7.0 (Firefox 7.0 / Thunderbird 7.0 / SeaMonkey 2.4), the non-standard and deprecated property
mozDashOffset
has been implemented. This property will be deprecated and removed in the future, see bug 931643. UselineDashOffset
instead.
WebKit-specific notes
- In WebKit-based browsers (e.g. Safari), the non-standard and deprecated property
webkitLineDashOffset
is implemented besides this method. UselineDashOffset
instead.
See also
- The interface defining it,
CanvasRenderingContext2D
CanvasRenderingContext2D.getLineDash()
CanvasRenderingContext2D.setLineDash()
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/api/canvasrenderingcontext2d/linedashoffset