From 95aca4b4d8fa62815d4bd412fff1a364f842814a Mon Sep 17 00:00:00 2001 From: Ryan Johnson Date: Thu, 29 Apr 2021 16:16:42 -0700 Subject: remove retired locales (#699) --- .../api/htmlcanvaselement/getcontext/index.html | 140 --------------------- 1 file changed, 140 deletions(-) delete mode 100644 files/vi/web/api/htmlcanvaselement/getcontext/index.html (limited to 'files/vi/web/api/htmlcanvaselement/getcontext') diff --git a/files/vi/web/api/htmlcanvaselement/getcontext/index.html b/files/vi/web/api/htmlcanvaselement/getcontext/index.html deleted file mode 100644 index b2478fba5d..0000000000 --- a/files/vi/web/api/htmlcanvaselement/getcontext/index.html +++ /dev/null @@ -1,140 +0,0 @@ ---- -title: HTMLCanvasElement.getContext() -slug: Web/API/HTMLCanvasElement/getContext -tags: - - TV -translation_of: Web/API/HTMLCanvasElement/getContext ---- -
{{APIRef("Canvas API")}}
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The HTMLCanvasElement.getContext() method returns a drawing context on the canvas, or {{jsxref("null")}} if the context identifier is not supported.

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Later calls to this method on the same canvas element return the same drawing context instance as was returned the last time the method was invoked with the same contextType argument. To get a different drawing context object you need to pass a different contextType or call the method on a different canvas element. 

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Syntax

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var ctx = canvas.getContext(contextType);
-var ctx = canvas.getContext(contextType, contextAttributes);
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Parameters

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contextType
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Is a {{domxref("DOMString")}} containing the context identifier defining the drawing context associated to the canvas. Possible values are: -
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  • "2d", leading to the creation of a {{domxref("CanvasRenderingContext2D")}} object representing a two-dimensional rendering context.
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  • "webgl" (or "experimental-webgl") which will create a {{domxref("WebGLRenderingContext")}} object representing a three-dimensional rendering context. This context is only available on browsers that implement WebGL version 1 (OpenGL ES 2.0).
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  • "webgl2" which will create a {{domxref("WebGL2RenderingContext")}} object representing a three-dimensional rendering context. This context is only available on browsers that implement WebGL version 2 (OpenGL ES 3.0). {{experimental_inline}}
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  • "bitmaprenderer" which will create an {{domxref("ImageBitmapRenderingContext")}} which only provides functionality to replace the content of the canvas with a given {{domxref("ImageBitmap")}}.
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Note: The identifier "experimental-webgl" is used in new implementations of WebGL. These implementations have either not reached test suite conformance, or the graphics drivers on the platform are not yet stable. The Khronos Group certifies WebGL implementations under certain conformance rules.

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

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const gl = canvas.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.
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  • {{non-standard_inline}} (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 {{domxref("CanvasRenderingContext2D.getImageData", "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).
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  • {{non-standard_inline}} (Blink only) storage: String that indicates which storage is used ("persistent" by default).
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- WebGL context attributes: - -
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  • alpha: Boolean that indicates if the canvas contains an alpha buffer.
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  • antialias: Boolean that indicates whether or not to perform anti-aliasing.
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  • depth: Boolean that indicates that the drawing buffer has a depth buffer of at least 16 bits.
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  • failIfMajorPerformanceCaveat: Boolean that indicates if a context will be created if the system performance is low.
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  • powerPreference: A hint to the user agent indicating what configuration of GPU is suitable for the WebGL context. Possible values are: -
      -
    • "default": Let the user agent decide which GPU configuration is most suitable. This is the default value.
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    • "high-performance": Prioritizes rendering performance over power consumption.
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    • "low-power": Prioritizes power saving over rendering performance.
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    -
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  • premultipliedAlpha: Boolean that indicates that the page compositor will assume the drawing buffer contains colors with pre-multiplied alpha.
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  • preserveDrawingBuffer: If the value is true the buffers will not be cleared and will preserve their values until cleared or overwritten by the author.
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  • stencil: Boolean that indicates that the drawing buffer has a stencil buffer of at least 8 bits.
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Return value

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A {{domxref("RenderingContext")}} which is either a

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

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Examples

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Given this {{HTMLElement("canvas")}} element:

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<canvas id="canvas" width="300" height="300"></canvas>
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You can get a 2d context of the canvas with the following code:

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var canvas = document.getElementById('canvas');
-var ctx = canvas.getContext('2d');
-console.log(ctx); // CanvasRenderingContext2D { ... }
-
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Now you have the 2D rendering context for a canvas and you can draw within it.

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Specifications

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SpecificationStatusComment
{{SpecName('HTML WHATWG', "scripting.html#dom-canvas-getcontext", "HTMLCanvasElement.getContext")}}{{Spec2('HTML WHATWG')}}No change since the latest snapshot, {{SpecName('HTML5 W3C')}}
{{SpecName('HTML5.1', "semantics-scripting.html#dom-htmlcanvaselement-getcontext", "HTMLCanvasElement.getContext")}}{{Spec2('HTML5.1')}}
{{SpecName('HTML5 W3C', "scripting-1.html#dom-canvas-getcontext", "HTMLCanvasElement.getContext")}}{{Spec2('HTML5 W3C')}}Snapshot of the {{SpecName('HTML WHATWG')}} containing the initial definition.
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Browser compatibility

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{{Compat("api.HTMLCanvasElement.getContext")}}

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See also

- - -- cgit v1.2.3-54-g00ecf