CanvasRenderingContext2D.addHitRegion()
This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.
The CanvasRenderingContext2D
.addHitRegion()
method of the Canvas 2D API adds a hit region to the bitmap. This allows you to make hit detection easier, lets you route events to DOM elements, and makes it possible for users to explore the canvas without seeing it.
Syntax
void <var>ctx.addHitRegion(options);</var>
Options
The options
argument is optional. When provided, it is an Object
which can contain the following properties:
path
- A
Path2D
object describing the area of the hit region. If not provided, the current path is used. fillRule
- The fill rule to use (defaults to "
nonzero
"). id
- The ID for this hit region to reference it for later use in events, for example.
parentID
- The ID of the parent region for cursor fallback and navigation by accessibility tools.
cursor
- The
cursor
to use when the mouse is over this region (defaults to "inherit
"). Inherits the cursor of the parent hit region, if any, or the canvas element's cursor. control
- An element (descendant of the canvas) to which events are to be routed. Defaults to
null
. label
- A text label for accessibility tools to use as a description of the region, if there is no control. Defaults to
null
. role
- An ARIA role for accessibility tools to determine how to represent this region, if there is no control. Defaults to
null
.
Examples
Using the addHitRegion
method
This is just a simple code snippet which uses the addHitRegion
method.
HTML
<canvas id="canvas"></canvas>
JavaScript
var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); canvas.addEventListener("mousemove", function(event){ if(event.region) { alert("ouch, my eye :("); } }); ctx.beginPath(); ctx.arc(100, 100, 75, 0, 2 * Math.PI, false); ctx.lineWidth = 5; ctx.stroke(); // eyes ctx.beginPath(); ctx.arc(70, 80, 10, 0, 2 * Math.PI, false); ctx.arc(130, 80, 10, 0, 2 * Math.PI, false); ctx.fill(); ctx.addHitRegion({id: "eyes"}); // mouth ctx.beginPath(); ctx.arc(100, 110, 50, 0, Math.PI, false); ctx.stroke();
Edit the code below and see your changes update live in the canvas (if you don't see the full smiley, check in the browser compatibility table, if your current browser supports hit regions already, you might need to activate a preference).
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:250px"> ctx.beginPath(); ctx.arc(100, 100, 75, 0, 2 * Math.PI, false); ctx.lineWidth = 5; ctx.stroke(); // eyes ctx.beginPath(); ctx.arc(70, 80, 10, 0, 2 * Math.PI, false); ctx.arc(130, 80, 10, 0, 2 * Math.PI, false); ctx.fill(); ctx.addHitRegion({id: "eyes"}); // mouth ctx.beginPath(); ctx.arc(100, 110, 50, 0, Math.PI, false); 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(); }); canvas.addEventListener("mousemove", function(event){ if(event.region) { alert("ouch, my eye :("); } }); textarea.addEventListener("input", drawCanvas); window.addEventListener("load", drawCanvas);
Specifications
Specification | Status | Comment |
---|---|---|
WHATWG HTML Living Standard The definition of 'CanvasRenderingContext2D.addHitRegion' in that specification. |
Living Standard | Initial definition. |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support |
(Yes)[1] | 30 (30) [2] | No support | No support | No support |
id |
(Yes)[1] | 30 (30) [2] | No support | No support | No support |
control |
(Yes)[1] | 30 (30) [2] | No support | No support | No support |
path |
(Yes)[1] | 39 (39) [2] | No support | No support | No support |
fillRule |
(Yes)[1] | No support | No support | No support | No support |
other hit region options | No support | No support | No support | No support | No support |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | No support | 30.0 (30) | No support | No support | No support |
id |
No support | No support | 30.0 (30) | No support | No support | No support |
control |
No support | No support | 30.0 (30) | No support | No support | No support |
path |
No support | No support | 39.0 (39) | No support | No support | No support |
fillRule |
No support | No support | No support | No support | No support | No support |
other hit region options | No support | No support | No support | No support | No support | No support |
[1] This feature is behind a feature flag. Set the flag ExperimentalCanvasFeatures
to true
to enable it.
[2] This feature is behind a feature preference setting. In about:config, set canvas.hitregions.enabled
to true
.
See also
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/addhitregion