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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 ---- -<div>{{APIRef("Canvas API")}}</div> - -<p><span class="seoSummary">The <strong><code>HTMLCanvasElement.getContext()</code></strong> method returns a drawing context on the canvas, or {{jsxref("null")}} if the context identifier is not supported.</span></p> - -<p>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 <code>contextType</code> argument. To get a different drawing context object you need to pass a different <code>contextType</code> or call the method on a different canvas element. </p> - -<h2 id="Syntax">Syntax</h2> - -<pre class="syntaxbox">var <em>ctx</em> = <em>canvas</em>.getContext(<em>contextType</em>); -var <em>ctx</em> = <em>canvas</em>.getContext(<em>contextType</em>, <em>contextAttributes</em>); -</pre> - -<h3 id="Parameters">Parameters</h3> - -<dl> - <dt><code>contextType</code></dt> - <dd>Is a {{domxref("DOMString")}} containing the context identifier defining the drawing context associated to the canvas. Possible values are: - <ul> - <li><code>"2d"</code>, leading to the creation of a {{domxref("CanvasRenderingContext2D")}} object representing a two-dimensional rendering context.</li> - <li><code>"webgl"</code> (or <code>"experimental-webgl"</code>) which will create a {{domxref("WebGLRenderingContext")}} object representing a three-dimensional rendering context. This context is only available on browsers that implement <a href="https://developer.mozilla.org/en-US/docs/Web/WebGL">WebGL</a> version 1 (OpenGL ES 2.0).</li> - <li><code>"webgl2"</code> which will create a {{domxref("WebGL2RenderingContext")}} object representing a three-dimensional rendering context. This context is only available on browsers that implement <a href="https://developer.mozilla.org/en-US/docs/Web/WebGL">WebGL</a> version 2 (OpenGL ES 3.0). {{experimental_inline}}</li> - <li><code>"bitmaprenderer"</code> which will create an {{domxref("ImageBitmapRenderingContext")}} which only provides functionality to replace the content of the canvas with a given {{domxref("ImageBitmap")}}.</li> - </ul> - - <div class="note"> - <p><strong>Note</strong>: The identifier <code>"experimental-webgl"</code> 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 <a href="https://www.khronos.org/">Khronos Group</a> certifies WebGL implementations under certain <a href="https://www.khronos.org/registry/webgl/sdk/tests/CONFORMANCE_RULES.txt">conformance rules</a>.</p> - </div> - </dd> - <dt><code>contextAttributes</code></dt> - <dd> - <p>You can use several context attributes when creating your rendering context, for example:</p> - - <pre class="brush: js">const gl = canvas.getContext('webgl', { - antialias: false, - depth: false -});</pre> - 2d context attributes: - - <ul> - <li><strong><code>alpha</code></strong>: Boolean that indicates if the canvas contains an alpha channel. If set to <code>false</code>, the browser now knows that the backdrop is always opaque, which can speed up drawing of transparent content and images.</li> - <li>{{non-standard_inline}} (Gecko only) <strong><code>willReadFrequently</code></strong>: 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 <code>gfx.canvas.willReadFrequently.enable</code> is set to <code>true</code> (which, by default, is only the case for B2G/Firefox OS).</li> - <li>{{non-standard_inline}} (Blink only) <strong><code>storage</code></strong>: String that indicates which storage is used ("persistent" by default).</li> - </ul> - WebGL context attributes: - - <ul> - <li><strong><code>alpha</code></strong>: Boolean that indicates if the canvas contains an alpha buffer.</li> - <li><strong><code>antialias</code></strong>: Boolean that indicates whether or not to perform anti-aliasing.</li> - <li><strong><code>depth</code></strong>: Boolean that indicates that the drawing buffer has a depth buffer of at least 16 bits.</li> - <li><code><strong>failIfMajorPerformanceCaveat</strong></code>: Boolean that indicates if a context will be created if the system performance is low.</li> - <li><code><strong>powerPreference</strong></code>: A hint to the user agent indicating what configuration of GPU is suitable for the WebGL context. Possible values are: - <ul> - <li><code>"default"</code>: Let the user agent decide which GPU configuration is most suitable. This is the default value.</li> - <li><code>"high-performance"</code>: Prioritizes rendering performance over power consumption.</li> - <li><code>"low-power"</code>: Prioritizes power saving over rendering performance.</li> - </ul> - </li> - <li><strong><code>premultipliedAlpha</code></strong>: Boolean that indicates that the page compositor will assume the drawing buffer contains colors with pre-multiplied alpha.</li> - <li><strong><code>preserveDrawingBuffer</code></strong>: If the value is true the buffers will not be cleared and will preserve their values until cleared or overwritten by the author.</li> - <li><strong><code>stencil</code></strong>: Boolean that indicates that the drawing buffer has a stencil buffer of at least 8 bits.</li> - </ul> - </dd> -</dl> - -<h3 id="Return_value">Return value</h3> - -<p>A {{domxref("RenderingContext")}} which is either a</p> - -<ul> - <li>{{domxref("CanvasRenderingContext2D")}} for <code>"2d"</code>,</li> - <li>{{domxref("WebGLRenderingContext")}} for <code>"webgl"</code> and <code>"experimental-webgl"</code>,</li> - <li>{{domxref("WebGL2RenderingContext")}} for <code>"webgl2"</code> or</li> - <li>{{domxref("ImageBitmapRenderingContext")}} for <code>"bitmaprenderer"</code>.</li> -</ul> - -<p>If the <code>contextType</code> doesn't match a possible drawing context, <code>null</code> is returned.</p> - -<h2 id="Examples">Examples</h2> - -<p>Given this {{HTMLElement("canvas")}} element:</p> - -<pre class="brush: html"><canvas id="canvas" width="300" height="300"></canvas> -</pre> - -<p>You can get a <code>2d</code> context of the canvas with the following code:</p> - -<pre class="brush: js">var canvas = document.getElementById('canvas'); -var ctx = canvas.getContext('2d'); -console.log(ctx); // CanvasRenderingContext2D { ... } -</pre> - -<p>Now you have the <a href="/en-US/docs/Web/API/CanvasRenderingContext2D">2D rendering context</a> for a canvas and you can draw within it.</p> - -<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('HTML WHATWG', "scripting.html#dom-canvas-getcontext", "HTMLCanvasElement.getContext")}}</td> - <td>{{Spec2('HTML WHATWG')}}</td> - <td>No change since the latest snapshot, {{SpecName('HTML5 W3C')}}</td> - </tr> - <tr> - <td>{{SpecName('HTML5.1', "semantics-scripting.html#dom-htmlcanvaselement-getcontext", "HTMLCanvasElement.getContext")}}</td> - <td>{{Spec2('HTML5.1')}}</td> - <td></td> - </tr> - <tr> - <td>{{SpecName('HTML5 W3C', "scripting-1.html#dom-canvas-getcontext", "HTMLCanvasElement.getContext")}}</td> - <td>{{Spec2('HTML5 W3C')}}</td> - <td>Snapshot of the {{SpecName('HTML WHATWG')}} containing the initial definition.</td> - </tr> - </tbody> -</table> - -<h2 id="Browser_compatibility">Browser compatibility</h2> - - - -<p>{{Compat("api.HTMLCanvasElement.getContext")}}</p> - -<h2 id="See_also">See also</h2> - -<ul> - <li>The interface defining it, {{domxref("HTMLCanvasElement")}}.</li> - <li>{{domxref("OffscreenCanvas.getContext()")}}</li> - <li>Available rendering contexts: {{domxref("CanvasRenderingContext2D")}}, {{domxref("WebGLRenderingContext")}} and {{domxref("WebGL2RenderingContext")}} and {{domxref("ImageBitmapRenderingContext")}}.</li> -</ul> |