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diff --git a/files/es/web/api/htmlcanvaselement/toblob/index.html b/files/es/web/api/htmlcanvaselement/toblob/index.html new file mode 100644 index 0000000000..4759cd6250 --- /dev/null +++ b/files/es/web/api/htmlcanvaselement/toblob/index.html @@ -0,0 +1,261 @@ +--- +title: HTMLCanvasElement.toBlob() +slug: Web/API/HTMLCanvasElement/toBlob +translation_of: Web/API/HTMLCanvasElement/toBlob +--- +<div> +<div> +<div>{{APIRef("Canvas API")}}</div> +</div> +</div> + +<p>EL metodo <strong><code>HTMLCanvasElement.toBlob()</code></strong> crea un objeto {{domxref("Blob")}} que representa la imagen contenida en el canvas; este archivo puede ser cacheado en el disco oo guardado en la memoria a desicion del user agent. Si la propiedad <code>type</code> no se especifica el tipo de la imagen será <code>image/png</code>. La imagen creada tiene una resolución de 96dpi.<br> + El tercer argumento es usado con las imagenes <code>image/jpeg</code> para especificar la calidad de salida.</p> + +<h2 id="Syntax">Syntax</h2> + +<pre class="syntaxbox"><var>void <em>canvas</em>.toBlob(<em>callback</em>, <em>type</em>, <em>encoderOptions</em>);</var> +</pre> + +<h3 id="Parameters">Parameters</h3> + +<dl> + <dt>callback</dt> + <dd>A callback function with the resulting {{domxref("Blob")}} object as a single argument.</dd> + <dt><code>type</code> {{optional_inline}}</dt> + <dd>A {{domxref("DOMString")}} indicating the image format. The default type is <code>image/png</code>.</dd> + <dt><code>encoderOptions</code> {{optional_inline}}</dt> + <dd>A {{jsxref("Number")}} between <code>0</code> and <code>1</code> indicating image quality if the requested type is <code>image/jpeg </code>or <code>image/webp</code>. If this argument is anything else, the default value for image quality is used. Other arguments are ignored.</dd> +</dl> + +<h3 id="Return_value">Return value</h3> + +<p>None.</p> + +<h2 id="Examples">Examples</h2> + +<h3 id="Getting_a_file_representing_the_canvas">Getting a file representing the canvas</h3> + +<p>Once you have drawn content into a canvas, you can convert it into a file of any supported image format. The code snippet below, for example, takes the image in the {{HTMLElement("canvas")}} element whose ID is "canvas", obtains a copy of it as a PNG image, then appends a new {{HTMLElement("img")}} element to the document, whose source image is the one created using the canvas.</p> + +<pre class="brush: js">var canvas = document.getElementById("canvas"); + +canvas.toBlob(function(blob) { + var newImg = document.createElement("img"), + url = URL.createObjectURL(blob); + + newImg.onload = function() { + // no longer need to read the blob so it's revoked + URL.revokeObjectURL(url); + }; + + newImg.src = url; + document.body.appendChild(newImg); +}); +</pre> + +<p>Note that here we're creating a PNG image; if you add a second parameter to the <code>toBlob()</code> call, you can specify the image type. For example, to get the image in JPEG format:</p> + +<pre class="brush: js"> canvas.toBlob(function(blob){...}, "image/jpeg", 0.95); // JPEG at 95% quality</pre> + +<div> +<h3 id="A_way_to_convert_a_canvas_to_an_ico_(Mozilla_only)">A way to convert a canvas to an ico (Mozilla only)</h3> + +<p>This uses <code>-moz-parse</code> to convert the canvas to ico. Windows XP doesn't support converting from PNG to ico, so it uses bmp instead. A download link is created by setting the download attribute. The value of the download attribute is the name it will use as the file name.</p> + +<pre class="brush: js">var canvas = document.getElementById("canvas"); +var d = canvas.width; +ctx = canvas.getContext("2d"); +ctx.beginPath(); +ctx.moveTo(d / 2, 0); +ctx.lineTo(d, d); +ctx.lineTo(0, d); +ctx.closePath(); +ctx.fillStyle = "yellow"; +ctx.fill(); + +function blobCallback(iconName) { + return function(b) { + var a = document.createElement("a"); + a.textContent = "Download"; + document.body.appendChild(a); + a.style.display = "block"; + a.download = iconName + ".ico"; + a.href = window.URL.createObjectURL(b); + } +} +canvas.toBlob(blobCallback('passThisString'), 'image/vnd.microsoft.icon', + '-moz-parse-options:format=bmp;bpp=32');</pre> +</div> + +<h3 id="Save_toBlob_to_disk_with_OS.File_(chromeadd-on_context_only)">Save toBlob to disk with OS.File (chrome/add-on context only)</h3> + +<div class="note"> +<p>This technique saves it to the desktop and is only useful in Firefox chrome context or add-on code as OS APIs are not present on web sites.</p> +</div> + +<pre class="brush: js">var canvas = document.getElementById("canvas"); +var d = canvas.width; +ctx = canvas.getContext("2d"); +ctx.beginPath(); +ctx.moveTo(d / 2, 0); +ctx.lineTo(d, d); +ctx.lineTo(0, d); +ctx.closePath(); +ctx.fillStyle = "yellow"; +ctx.fill(); + +function blobCallback(iconName) { + return function(b) { + var r = new FileReader(); + r.onloadend = function () { + // r.result contains the ArrayBuffer. + Cu.import('resource://gre/modules/osfile.jsm'); + var writePath = OS.Path.join(OS.Constants.Path.desktopDir, + iconName + '.ico'); + var promise = OS.File.writeAtomic(writePath, new Uint8Array(r.result), + {tmpPath:writePath + '.tmp'}); + promise.then( + function() { + console.log('successfully wrote file'); + }, + function() { + console.log('failure writing file') + } + ); + }; + r.readAsArrayBuffer(b); + } +} + +canvas.toBlob(blobCallback('passThisString'), 'image/vnd.microsoft.icon', + '-moz-parse-options:format=bmp;bpp=32');</pre> + +<h2 id="Polyfill">Polyfill</h2> + +<p>A low performance polyfill based on toDataURL.</p> + +<pre class="brush: js">if (!HTMLCanvasElement.prototype.toBlob) { + Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', { + value: function (callback, type, quality) { + + var binStr = atob( this.toDataURL(type, quality).split(',')[1] ), + len = binStr.length, + arr = new Uint8Array(len); + + for (var i=0; i<len; i++ ) { + arr[i] = binStr.charCodeAt(i); + } + + callback( new Blob( [arr], {type: type || 'image/png'} ) ); + } + }); +} +</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#dom-canvas-toblob", "HTMLCanvasElement.toBlob")}}</td> + <td>{{Spec2('HTML WHATWG')}}</td> + <td>No change since the latest snapshot, {{SpecName('HTML5 W3C')}}</td> + </tr> + <tr> + <td>{{SpecName('HTML5.1', "scripting-1.html#dom-canvas-toblob", "HTMLCanvasElement.toBlob")}}</td> + <td>{{Spec2('HTML5.1')}}</td> + <td>No change</td> + </tr> + <tr> + <td>{{SpecName('HTML5 W3C', "scripting-1.html#dom-canvas-toblob", "HTMLCanvasElement.toBlob")}}</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>{{CompatibilityTable}}</p> + +<div id="compat-desktop"> +<table class="compat-table"> + <tbody> + <tr> + <th>Feature</th> + <th>Chrome</th> + <th>Firefox (Gecko)</th> + <th>Internet Explorer</th> + <th>Opera</th> + <th>Safari</th> + </tr> + <tr> + <td>Basic support</td> + <td>{{CompatNo}}<sup>[1]</sup></td> + <td>{{CompatGeckoDesktop('19')}}</td> + <td>{{CompatIE(10)}}{{property_prefix("ms")}}</td> + <td>{{CompatNo}}</td> + <td>{{CompatNo}}<sup>[2]</sup></td> + </tr> + <tr> + <td>Image quality parameter (jpeg)</td> + <td>{{CompatNo}}</td> + <td>{{CompatGeckoDesktop('25')}}</td> + <td>{{CompatNo}}</td> + <td>{{CompatNo}}</td> + <td>{{CompatNo}}</td> + </tr> + </tbody> +</table> +</div> + +<div id="compat-mobile"> +<table class="compat-table"> + <tbody> + <tr> + <th>Feature</th> + <th>Android</th> + <th>Chrome for Android</th> + <th>Firefox Mobile (Gecko)</th> + <th>IE Mobile</th> + <th>Opera Mobile</th> + <th>Safari Mobile</th> + </tr> + <tr> + <td>Basic support</td> + <td>{{CompatNo}}</td> + <td>{{CompatNo}}</td> + <td>{{CompatGeckoMobile("19")}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatNo}}</td> + <td>{{CompatUnknown}}</td> + </tr> + <tr> + <td>Image quality parameter (jpeg)</td> + <td>{{CompatNo}}</td> + <td>{{CompatNo}}</td> + <td>{{CompatGeckoMobile("25")}}</td> + <td>{{CompatUnknown}}</td> + <td>{{CompatNo}}</td> + <td>{{CompatUnknown}}</td> + </tr> + </tbody> +</table> +</div> + +<p>[1] Chrome does not implement this feature yet. See <a href="http://crbug.com/67587">bug 67587</a>.</p> + +<p>[2] WebKit does not implement this feature yet. See {{WebKitBug("71270")}}.</p> + +<h2 id="See_also">See also</h2> + +<ul> + <li>The interface defining it, {{domxref("HTMLCanvasElement")}}.</li> + <li>{{domxref("Blob")}}</li> +</ul> |