OffscreenCanvas.getContext()

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This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

OffscreenCanvas.getContext() 메소드는 offscreen 캔버스를 위한 드로잉 컨텍스트 반환합니다. 컨텍스트 식별자가 지원되는 상황이 아닐 경우 null를 반환합니다.

Note: 이 API는 현재 WebGL1과 WebGL2 컨텍스트에서만 실행됩니다.  Canvas 2D API 관련 bug 801176를 참조하세요.

구문

offscreen.getContext(contextType, contextAttributes);

매개 변수

contextType
캔버스의 드로잉 컨텍스트를 정의하는 컨텍스트 식별자가 포함된 DOMString입니다:
  • "2d"는 2차원 렌더링 컨텍스트를 표현하는 CanvasRenderingContext2D 객체를 생성합니다.
  • "webgl"는 3차원 렌더링 컨텍스트를 표현하는 WebGLRenderingContext 객체를 생성합니다. 이 컨텍스트는 WebGL 버전 1(OpenGL ES 2.0)을 지원하는 브라우저에서만 사용 가능합니다.
  • "webgl2"는 3차원 렌더링 컨텍스트를 표현하는 WebGL2RenderingContext 객체를 생성합니다. 이 컨텍스트는 WebGL 버전 2 (OpenGL ES 3.0)를 지원하는 브라우저에서만 사용 가능합니다. 
  • "bitmaprenderer"는 주어진 ImageBitmap을 캔버스의 내용 대신 전환하는 함수를 제공하는 ImageBitmapRenderingContext를 생성합니다. 

Note:"experimental-webgl"과 "experimental-webgl2" 식별자는 WebGL에서도 사용됩니다. 그러나 아직 테스트 적합성을 통과하지 못했거나 플랫폼별 그래픽 드라이버 지원이 안정적이진 않습니다. Khronos Group은 특정한  정합성 규칙에 WebGL 구현을 인증하고 있습니다.

contextAttributes

You can use several context attributes when creating your rendering context, for example:

offscreen.getContext("webgl", 
                 { antialias: false,
                   depth: false });
2d context attributes:
  • alpha: Boolean that indicates if the canvas contains an alpha channel. If set to false, the browser now knows that the backdrop is always opaque, which can speed up drawing of transparent content and images then.
  • (Gecko only) willReadFrequently: Boolean that indicates whether or not a lot of read-back operations are planned. This will force the use of a software (instead of hardware accelerated) 2D canvas and can save memory when calling getImageData() frequently. This option is only available, if the flag gfx.canvas.willReadFrequently.enable is set to true (which, by default, is only the case for B2G/Firefox OS).
  • (Blink only) storage: String that indicates which storage is used ("persistent" by default).
WebGL context attributes:
  • alpha: Boolean that indicates if the canvas contains an alpha buffer.
  • depth: Boolean that indicates that the drawing buffer has a depth buffer of at least 16 bits.
  • stencil: Boolean that indicates that the drawing buffer has a stencil buffer of at least 8 bits.
  • antialias: Boolean that indicates whether or not to perform anti-aliasing.
  • premultipliedAlpha: Boolean that indicates that the page compositor will assume the drawing buffer contains colors with pre-multiplied alpha.
  • preserveDrawingBuffer: If the value is true the buffers will not be cleared and will preserve their values until cleared or overwritten by the author.
  • failIfMajorPerformanceCaveat: Boolean that indicates if a context will be created if the system performance is low.

Return value

A RenderingContext which is either a

If the contextType doesn't match a possible drawing context, null is returned.

Examples

var offscreen = new OffscreenCanvas(256, 256);
var gl = offscreen.getContext("webgl");

gl; // WebGLRenderingContext
gl.canvas; // OffscreenCanvas

Specifications

Specification Status Comment
HTML Living Standard
The definition of 'OffscreenCanvas.getContext()' in that specification.
Living Standard  

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
getContext
Experimental
Chrome Full support 69Edge ? Firefox Full support 44
Disabled
Full support 44
Disabled
Disabled From version 44: this feature is behind the gfx.offscreencanvas.enabled preference. To change preferences in Firefox, visit about:config.
IE No support NoOpera Full support 56Safari No support NoWebView Android No support NoChrome Android Full support 69Edge Mobile ? Firefox Android Full support 44
Disabled
Full support 44
Disabled
Disabled From version 44: this feature is behind the gfx.offscreencanvas.enabled preference. To change preferences in Firefox, visit about:config.
Opera Android Full support YesSafari iOS No support NoSamsung Internet Android No support No
WebGL context
Experimental
Chrome No support NoEdge ? Firefox Full support 44
Disabled
Full support 44
Disabled
Disabled From version 44: this feature is behind the gfx.offscreencanvas.enabled preference. To change preferences in Firefox, visit about:config.
IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile ? Firefox Android Full support 44
Disabled
Full support 44
Disabled
Disabled From version 44: this feature is behind the gfx.offscreencanvas.enabled preference. To change preferences in Firefox, visit about:config.
Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
webgl2 context
Experimental
Chrome No support NoEdge ? Firefox Full support 44
Disabled
Full support 44
Disabled
Disabled From version 44: this feature is behind the gfx.offscreencanvas.enabled preference. To change preferences in Firefox, visit about:config.
IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile ? Firefox Android Full support 44
Disabled
Full support 44
Disabled
Disabled From version 44: this feature is behind the gfx.offscreencanvas.enabled preference. To change preferences in Firefox, visit about:config.
Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
2d context
Experimental
Chrome No support NoEdge ? Firefox No support NoIE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile ? Firefox Android No support NoOpera Android No support NoSafari iOS No support NoSamsung Internet Android No support No
bitmaprenderer context
Experimental
Chrome No support NoEdge ? Firefox Full support 46
Disabled
Full support 46
Disabled
Disabled From version 46: this feature is behind the gfx.offscreencanvas.enabled preference. To change preferences in Firefox, visit about:config.
IE No support NoOpera No support NoSafari No support NoWebView Android No support NoChrome Android No support NoEdge Mobile ? Firefox Android Full support 46
Disabled
Full support 46
Disabled
Disabled From version 46: this feature is behind the gfx.offscreencanvas.enabled preference. To change preferences in Firefox, visit about:config.
Opera Android No support NoSafari iOS No support NoSamsung Internet Android No support No

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
User must explicitly enable this feature.
User must explicitly enable this feature.

See also

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