HTMLCanvasElement
HTMLCanvasElement 介面提供控制 canvas 元素的屬性和方法. HTMLCanvasElement 介面也繼承了 HTMLElement 介面的屬性和方法.
屬性
從父代繼承的屬性，HTMLElement.
HTMLCanvasElement.height(en-US)- Is a positive
integerreflecting theheightHTML attribute of the<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 of150is used. HTMLCanvasElement.mozOpaque(en-US)- Is a
Booleanreflecting themoz-opaqueHTML attribute of the<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. HTMLCanvasElement.width(en-US)- Is a positive
integerreflecting thewidthHTML attribute of the<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 of300is used. HTMLCanvasElement.mozPrintCallback- Is a
functionthat is Initially null, Web content can set this to a JavaScript function that will be called if the page is printed. This function can then redraw the canvas at a higher resolution that is suitable for the printer being used. See this blog post.
方法
從父代繼承的方法, HTMLElement.
HTMLCanvasElement.captureStream()(en-US)- Returns a
CanvasCaptureMediaStream(en-US) that is a real-time video capture of the surface of the canvas. HTMLCanvasElement.getContext()(en-US)- 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
"2d"returns aCanvasRenderingContext2Dobject, whereas calling it with"experimental-webgl"(or"webgl") returns aWebGLRenderingContext(en-US) object. This context is only available on browsers that implement WebGL. HTMLCanvasElement.toDataURL()- Returns a data-URL containing a representation of the image in the format specified by the
typeparameter (defaults topng). The returned image is in a resolution of 96dpi. HTMLCanvasElement.toBlob()(en-US)- Creates a
Blobobject 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. HTMLCanvasElement.mozGetAsFile()(en-US)- Returns a
Fileobject representing the image contained in the canvas; this file is a memory-based file, with the specifiedname. Iftypeis not specified, the image type isimage/png.
規範
| 規範 | 狀態 | 註 |
|---|---|---|
| Media Capture from DOM Elements The definition of 'HTMLCanvasElement' in that specification. |
Working Draft | Adds the method captureStream(). |
| HTML Living Standard The definition of 'HTMLCanvasElement' in that specification. |
Living Standard | The method getContext() now returns a RenderingContext rather than an opaque object.The methods probablySupportsContext(), setContext() and transferControlToProxy()have been added. |
| HTML 5.1 The definition of 'HTMLCanvasElement' in that specification. |
Recommendation | |
| HTML5 The definition of 'HTMLCanvasElement' in that specification. |
Recommendation | Initial definition. |
瀏覽器相容性
We're converting our compatibility data into a machine-readable JSON format.
This compatibility table still uses the old format,
because we haven't yet converted the data it contains.
Find out how you can help! (en-US)
| Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|---|
Basic support (2D context) |
4.0 | (Yes) | 3.6 (1.9.2) | 9.0 | 9.0 [1] | 3.1 |
toBlob() |
50 | No support | 19 (19) [2] | ? | ? | No support (bug 71270) |
probablySupportsContext(),setContext(),transferControlToProxy() |
No support | ? | No support | No support | No support | No support |
mozGetAsFile() |
No support | No support | 4.0 (2) | No support | No support | No support |
captureStream() |
No support | No support | 41 (41) | No support | No support | No support |
transferControlToOffscreen() |
No support | No support | 44 (44) [3] | No support | No support | No support |
| Feature | Android | Chrome for Android | Edge | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|---|
Basic support (2D context) |
2.1 | (Yes) | (Yes) | (Yes) | ? | 10.0 [1] | 3.2 |
webgl context |
? | ? | ? | (Yes) as experimental-webgl |
? | ? | ? |
toBlob() |
No support (bug 67587) | 50 | No support | 18.0 (18) [2] | ? | ? | No support (bug 71270) |
probablySupportsContext(),setContext(),transferControlToProxy() |
No support | No support | ? | No support | No support | No support | No support |
mozGetAsFile() |
No support | No support | No support | 4.0 (2) | No support | No support | No support |
captureStream() |
No support | No support | No support | 41.0 (41) | No support | No support | No support |
transferControlToOffscreen() |
No support | No support | No support | 44.0 (44) [3] | No support | No support | No support |
[1] Opera Mini 5.0 and later has partial support.
[2] Support for the third parameter, has been added in Gecko 25 only: when used with the "image/jpeg" type, this argument specifies the image quality.
[3] This feature is behind a feature preference setting. In about:config, set gfx.offscreencanvas.enabled to true.
See also
- HTML element implementing this interface:
<canvas>.