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+---
+title: OffscreenCanvas
+slug: Web/API/OffscreenCanvas
+tags:
+  - API
+  - Canvas
+  - Experimental
+  - Interface
+  - NeedsTranslation
+  - Reference
+  - TopicStub
+translation_of: Web/API/OffscreenCanvas
+---
+<div>{{APIRef("Canvas API")}} {{SeeCompatTable}}</div>
+
+<p>The <strong><code>OffscreenCanvas</code></strong> interface provides a canvas that can be rendered off screen. It is available in both the window and <a href="/en-US/docs/Web/API/Web_Workers_API">worker</a> contexts.</p>
+
+<h2 id="Constructors">Constructors</h2>
+
+<dl>
+ <dt>{{domxref("OffscreenCanvas.OffscreenCanvas", "OffscreenCanvas()")}}</dt>
+ <dd><code>OffscreenCanvas</code> constructor. Creates a new <code>OffscreenCanvas</code> object.</dd>
+</dl>
+
+<h2 id="Properties">Properties</h2>
+
+<dl>
+ <dt>{{domxref("OffscreenCanvas.height")}}</dt>
+ <dd>The height of the offscreen canvas.</dd>
+ <dt>{{domxref("OffscreenCanvas.width")}}</dt>
+ <dd>The width of the offscreen canvas.</dd>
+</dl>
+
+<h2 id="Methods">Methods</h2>
+
+<dl>
+ <dt>{{domxref("OffscreenCanvas.getContext()")}}</dt>
+ <dd>Returns a rendering context for the offscreen canvas.</dd>
+</dl>
+
+<dl>
+ <dt>{{domxref("OffscreenCanvas.convertToBlob()")}}</dt>
+ <dd>Creates a {{domxref("Blob")}} object representing the image contained in the canvas.</dd>
+</dl>
+
+<dl>
+ <dt>{{domxref("OffscreenCanvas.transferToImageBitmap()")}}</dt>
+ <dd>Creates an {{domxref("ImageBitmap")}} object from the most recently rendered image of the <code>OffscreenCanvas</code>.</dd>
+</dl>
+
+<h2 id="Examples">Examples</h2>
+
+<h3 id="Synchronous_display_of_frames_produced_by_an_OffscreenCanvas">Synchronous display of frames produced by an <code>OffscreenCanvas</code></h3>
+
+<p>One way to use the <code>OffscreenCanvas</code> API, is to use a {{domxref("RenderingContext")}} that has been obtained from an <code>OffscreenCanvas</code> object to generate new frames. Once a new frame has finished rendering in this context,  the {{domxref("OffscreenCanvas.transferToImageBitmap", "transferToImageBitmap()")}} method can be called to save the most recent rendered image. This method returns an {{domxref("ImageBitmap")}} object, which can be used in a variety of Web APIs and also in a second canvas without creating a transfer copy.</p>
+
+<p>To display the <code>ImageBitmap</code>, you can use a {{domxref("ImageBitmapRenderingContext")}} context, which can be created by calling <code>canvas.getContext("bitmaprenderer")</code> on a (visible) canvas element. This context only provides functionality to replace the canvas's contents with the given <code>ImageBitmap</code>. A call to {{domxref("ImageBitmapRenderingContext.transferFromImageBitmap()")}} with the previously rendered and saved <code>ImageBitmap</code> from the OffscreenCanvas, will display the <code>ImageBitmap</code> on the canvas and transfer its ownership to the canvas. A single <code>OffscreenCanvas</code> may transfer frames into an arbitrary number of other <code>ImageBitmapRenderingContext</code> objects.</p>
+
+<p>Given these two {{HTMLElement("canvas")}} elements</p>
+
+<pre class="brush: html notranslate">&lt;canvas id="one"&gt;&lt;/canvas&gt;
+&lt;canvas id="two"&gt;&lt;/canvas&gt;</pre>
+
+<p>the following code will provide the rendering using an <code>OffscreenCanvas</code> as described above.</p>
+
+<pre class="brush: js notranslate">var one = document.getElementById("one").getContext("bitmaprenderer");
+var two = document.getElementById("two").getContext("bitmaprenderer");
+
+var offscreen = new OffscreenCanvas(256, 256);
+var gl = offscreen.getContext('webgl');
+
+// ... some drawing for the first canvas using the gl context ...
+
+// Commit rendering to the first canvas
+var bitmapOne = offscreen.transferToImageBitmap();
+one.transferFromImageBitmap(bitmapOne);
+
+// ... some more drawing for the second canvas using the gl context ...
+
+// Commit rendering to the second canvas
+var bitmapTwo = offscreen.transferToImageBitmap();
+two.transferFromImageBitmap(bitmapTwo);
+</pre>
+
+<h3 id="Asynchronous_display_of_frames_produced_by_an_OffscreenCanvas">Asynchronous display of frames produced by an <code>OffscreenCanvas</code></h3>
+
+<p>Another way to use the <code>OffscreenCanvas</code> API, is to call {{domxref("HTMLCanvasElement.transferControlToOffscreen", "transferControlToOffscreen()")}} on a {{HTMLElement("canvas")}} element, either on a <a href="/en-US/docs/Web/API/Web_Workers_API">worker</a> or the main thread, which will return an <code>OffscreenCanvas</code> object from an {{domxref("HTMLCanvasElement")}} object from the main thread. Calling {{domxref("OffscreenCanvas.getContext", "getContext()")}} will then obtain a <code>RenderingContext</code> from that <code>OffscreenCanvas</code>.</p>
+
+<p>main.js (main thread code):</p>
+
+<pre class="brush: js notranslate">var htmlCanvas = document.getElementById("canvas");
+var offscreen = htmlCanvas.transferControlToOffscreen();
+
+var worker = new Worker("offscreencanvas.js");
+worker.postMessage({canvas: offscreen}, [offscreen]);
+</pre>
+
+<p>offscreencanvas.js (worker code):</p>
+
+<pre class="brush: js notranslate">onmessage = function(evt) {
+  var canvas = evt.data.canvas;
+  var gl = canvas.getContext("webgl");
+
+  // ... some drawing using the gl context ...
+};
+</pre>
+
+<p>You can also use requestAnimationFrame in workers</p>
+
+<pre class="brush: js notranslate">onmessage = function(evt) {
+  const canvas = evt.data.canvas;
+  const gl = canvas.getContext("webgl");
+
+  function render(time) {
+    // ... some drawing using the gl context ...
+    requestAnimationFrame(render);
+  }
+  requestAnimationFrame(render);
+};</pre>
+
+<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#the-offscreencanvas-interface", "OffscreenCanvas")}}</td>
+   <td>{{Spec2('HTML WHATWG')}}</td>
+   <td> </td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Browser_compatibility">Browser compatibility</h2>
+
+<div>
+
+
+<p>{{Compat("api.OffscreenCanvas")}}</p>
+</div>
+
+<h2 id="See_also">See also</h2>
+
+<ul>
+ <li><a href="https://hacks.mozilla.org/2016/01/webgl-off-the-main-thread/">WebGL Off the Main Thread – Mozilla Hacks</a></li>
+ <li>{{domxref("CanvasRenderingContext2D")}}</li>
+ <li>{{domxref("ImageBitmap")}}</li>
+ <li>{{domxref("ImageBitmapRenderingContext")}}</li>
+ <li>{{domxref("HTMLCanvasElement.transferControlToOffscreen()")}}</li>
+ <li>{{domxref("WebGLRenderingContext.commit()")}}</li>
+</ul>