1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
|
---
title: HTMLCanvasElement
slug: Web/API/HTMLCanvasElement
tags:
- API
- Canvas
- HTML DOM
- Interface
- NeedsTranslation
- Reference
- TopicStub
translation_of: Web/API/HTMLCanvasElement
---
<div>
<div>{{APIRef("Canvas API")}}</div>
</div>
<p>The <strong><code>HTMLCanvasElement</code></strong> interface provides properties and methods for manipulating the layout and presentation of {{HtmlElement("canvas")}} elements. The <code>HTMLCanvasElement</code> interface also inherits the properties and methods of the {{domxref("HTMLElement")}} interface.</p>
<p>{{InheritanceDiagram(600, 120)}}</p>
<h2 id="Properties">Properties</h2>
<p><em>Inherits properties from its parent, </em><em>{{domxref("HTMLElement")}}.</em></p>
<dl>
<dt>{{domxref("HTMLCanvasElement.height")}}</dt>
<dd>Is a positive <code>integer</code> reflecting the {{htmlattrxref("height", "canvas")}} HTML attribute of the {{HTMLElement("canvas")}} element interpreted in CSS pixels. When the attribute is not specified, or if it is set to an invalid value, like a negative, the default value of <code>150</code> is used.</dd>
<dt>{{domxref("HTMLCanvasElement.width")}}</dt>
<dd>Is a positive <code>integer</code> reflecting the {{htmlattrxref("width", "canvas")}} HTML attribute of the {{HTMLElement("canvas")}} element interpreted in CSS pixels. When the attribute is not specified, or if it is set to an invalid value, like a negative, the default value of <code>300</code> is used.</dd>
<dt>{{domxref("HTMLCanvasElement.mozOpaque")}} {{non-standard_inline}} {{deprecated_inline}}</dt>
<dd>Is a {{jsxref("Boolean")}} reflecting the {{htmlattrxref("moz-opaque", "canvas")}} HTML attribute of the {{HTMLElement("canvas")}} element. It lets the canvas know whether or not translucency will be a factor. If the canvas knows there's no translucency, painting performance can be optimized. This is only supported in Mozilla-based browsers; use the standardized {{domxref("HTMLCanvasElement.getContext()", "canvas.getContext('2d', { alpha: false })")}} instead.</dd>
<dt>{{domxref("HTMLCanvasElement.mozPrintCallback")}}{{non-standard_inline}}</dt>
<dd>Is a <code>function</code> that is Initially null. Web content can set this to a JavaScript function that will be called when the canvas is to be redrawn while the page is being printed. When called, the callback is passed a "printState" object that implements the <a href="https://searchfox.org/mozilla-central/search?q=interface MozCanvasPrintState&path=HTMLCanvasElement.webidl">MozCanvasPrintState</a> interface. The callback can get the context to draw to from the printState object and must then call done() on it when finished. The purpose of <code>mozPrintCallback</code> is to obtain a higher resolution rendering of the canvas at the resolution of the printer being used. <a href="https://blog.mozilla.org/labs/2012/09/a-new-way-to-control-printing-output/">See this blog post.</a></dd>
</dl>
<h2 id="Methods">Methods</h2>
<p><em>Inherits methods from its parent, </em><em>{{domxref("HTMLElement")}}.</em></p>
<dl>
<dt>{{domxref("HTMLCanvasElement.captureStream()")}} {{experimental_inline}}</dt>
<dd>Returns a {{domxref("CanvasCaptureMediaStream")}} that is a real-time video capture of the surface of the canvas.</dd>
<dt>{{domxref("HTMLCanvasElement.getContext()")}}</dt>
<dd>Returns a drawing context on the canvas, or null if the context ID is not supported. A drawing context lets you draw on the canvas. Calling getContext with <code>"2d"</code> returns a {{domxref("CanvasRenderingContext2D")}} object, whereas calling it with <code>"webgl"</code> (or <code>"experimental-webgl"</code>) returns a {{domxref("WebGLRenderingContext")}} object. This context is only available on browsers that implement <a href="/en-US/docs/Web/WebGL">WebGL</a>.</dd>
<dt>{{domxref("HTMLCanvasElement.toDataURL()")}}</dt>
<dd>Returns a data-URL containing a representation of the image in the format specified by the <code>type</code> parameter (defaults to <code>png</code>). The returned image is in a resolution of 96dpi.</dd>
<dt>{{domxref("HTMLCanvasElement.toBlob()")}}</dt>
<dd>Creates a {{domxref("Blob")}} object representing the image contained in the canvas; this file may be cached on the disk or stored in memory at the discretion of the user agent.</dd>
<dt>{{domxref("HTMLCanvasElement.transferControlToOffscreen()")}} {{experimental_inline}}</dt>
<dd>Transfers control to an {{domxref("OffscreenCanvas")}} object, either on the main thread or on a worker.</dd>
<dt>{{domxref("HTMLCanvasElement.mozGetAsFile()")}} {{non-standard_inline}} {{deprecated_inline}}</dt>
<dd>Returns a {{domxref("File")}} object representing the image contained in the canvas; this file is a memory-based file, with the specified <code>name</code>. If <code>type</code> is not specified, the image type is <code>image/png</code>.</dd>
</dl>
<h2 id="Events">Events</h2>
<p>Listen to these events using <code><a href="/en-US/docs/Web/API/EventTarget/addEventListener">addEventListener()</a></code>.</p>
<dl>
<dt><code><a href="/en-US/docs/Web/API/HTMLCanvasElement/webglcontextcreationerror_event">webglcontextcreationerror</a></code></dt>
<dd>Fired if the user agent is unable to create a <code>WebGLRenderingContext</code> or <code>WebGL2RenderingContext</code> context.</dd>
<dt><code><a href="/en-US/docs/Web/API/HTMLCanvasElement/webglcontextlost_event">webglcontextlost</a></code></dt>
<dd>Fired if the user agent detects that the drawing buffer associated with a <code>WebGLRenderingContext</code> or <code>WebGL2RenderingContext</code> object has been lost.</dd>
<dt><code><a href="/en-US/docs/Web/API/HTMLCanvasElement/webglcontextrestored_event">webglcontextrestored</a></code></dt>
<dd>Fired if the user agent restores the drawing buffer for a <code>WebGLRenderingContext</code> or <code>WebGL2RenderingContext</code> object.</dd>
</dl>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>{{SpecName('Media Capture DOM Elements', '#html-media-element-media-capture-extensions', 'HTMLCanvasElement')}}</td>
<td>{{Spec2('Media Capture DOM Elements')}}</td>
<td>Adds the method <code>captureStream()</code>.</td>
</tr>
<tr>
<td>{{SpecName('HTML WHATWG', "#htmlcanvaselement", "HTMLCanvasElement")}}</td>
<td>{{Spec2('HTML WHATWG')}}</td>
<td>The method <code>getContext()</code> now returns a {{domxref("RenderingContext")}} rather than an opaque <code>object</code>.<br>
The <code>transferControlToOffscreen()</code>method has been added.</td>
</tr>
<tr>
<td>{{SpecName('HTML5.1', "scripting-1.html#the-canvas-element", "HTMLCanvasElement")}}</td>
<td>{{Spec2('HTML5.1')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('HTML5 W3C', "scripting-1.html#the-canvas-element", "HTMLCanvasElement")}}</td>
<td>{{Spec2('HTML5 W3C')}}</td>
<td>Initial definition.</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<div>
<p>{{Compat("api.HTMLCanvasElement")}}</p>
</div>
<h2 id="See_also">See also</h2>
<ul>
<li>HTML element implementing this interface: {{HTMLElement("canvas")}}</li>
</ul>
|
