--- title: CanvasRenderingContext2D.globalCompositeOperation slug: Web/API/CanvasRenderingContext2D/globalCompositeOperation tags: - Canvas - CanvasRenderingContext2D translation_of: Web/API/CanvasRenderingContext2D/globalCompositeOperation --- <div>{{APIRef}}</div> <p>Canvas 2D API的 <code><strong>CanvasRenderingContext2D</strong></code><strong><code>.globalCompositeOperation</code></strong> 属性设置要在绘制新形状时应用的合成操作的类型,其中type是用于标识要使用的合成或混合模式操作的字符串。</p> <p>在 <a href="/en-US/docs/Web/API/Canvas_API/Tutorial">Canvas Tutorial</a> 中查看 <a href="/en-US/docs/Web/API/Canvas_API/Tutorial/Compositing">Compositing</a> 章节。</p> <h2 id="语法">语法</h2> <pre class="syntaxbox"><var><em>ctx</em>.globalCompositeOperation = type;</var></pre> <h3 id="类型">类型</h3> <p>{{EmbedLiveSample("合成示例", 750, 6750, "" ,"Web/API/Canvas_API/Tutorial/Compositing/Example")}}</p> <h2 id="示例">示例</h2> <h3 id="Using_the_globalAlpha_property" name="Using_the_globalAlpha_property">使用 <code>globalCompositeOperation</code> 属性</h3> <p>这是一段使用 <code>globalCompositeOperation</code> 属性的简单的代码片段,绘制了2个矩形在重叠时相互排斥的情况。</p> <h4 id="HTML">HTML</h4> <pre class="brush: html"><canvas id="canvas"></canvas> </pre> <h4 id="JavaScript">JavaScript</h4> <pre class="brush: js; highlight[4]">var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); ctx.globalCompositeOperation = "xor"; ctx.fillStyle = "blue"; ctx.fillRect(10, 10, 100, 100); ctx.fillStyle = "red"; ctx.fillRect(50, 50, 100, 100); </pre> <p>修改下面的代码并在线查看 canvas 的变化:</p> <div class="hidden"> <h6 id="Playable_code" name="Playable_code">Playable code</h6> <pre class="brush: html"><canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas> <div class="playable-buttons"> <input id="edit" type="button" value="Edit" /> <input id="reset" type="button" value="Reset" /> </div> <textarea id="code" class="playable-code" style="height:120px;"> ctx.globalCompositeOperation = "xor"; ctx.fillStyle = "blue"; ctx.fillRect(10, 10, 100, 100); ctx.fillStyle = "red"; ctx.fillRect(50, 50, 100, 100);</textarea> </pre> <pre class="brush: js">var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); var textarea = document.getElementById("code"); var reset = document.getElementById("reset"); var edit = document.getElementById("edit"); var code = textarea.value; function drawCanvas() { ctx.clearRect(0, 0, canvas.width, canvas.height); eval(textarea.value); } reset.addEventListener("click", function() { textarea.value = code; drawCanvas(); }); edit.addEventListener("click", function() { textarea.focus(); }) textarea.addEventListener("input", drawCanvas); window.addEventListener("load", drawCanvas); </pre> </div> <p>{{ EmbedLiveSample('Playable_code', 700, 380) }}</p> <h2 id="规范描述">规范描述</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-context-2d-globalcompositeoperation", "CanvasRenderingContext2D.globalCompositeOperation")}}</td> <td>{{Spec2('HTML WHATWG')}}</td> <td></td> </tr> <tr> <td>{{SpecName('Compositing')}}</td> <td>{{Spec2('Compositing')}}</td> <td></td> </tr> </tbody> </table> <h2 id="浏览器兼容性">浏览器兼容性</h2> <p>{{Compat("api.CanvasRenderingContext2D.globalCompositeOperation")}}</p> <h3 id="WebKitBlink-specific_注解">WebKit/Blink-specific 注解</h3> <ul> <li>在基于 WebKit- 和 Blink- 的浏览器中,除了此属性外,还实现了一个不标准的并且不赞成使用的方法 <code>ctx.setCompositeOperation()</code>。</li> </ul> <h3 id="Gecko-specific_注解">Gecko-specific 注解</h3> <ul> <li>早起的规范草案指定了 "darker"值。 然而, Firefox 在第4个版本({{bug(571532)}})移除了对 "darker"的支持。参见 <a href="http://dropshado.ws/post/77229081704/firefox-doesnt-support-canvas-composite-darker">这篇文章</a> 建议如何使用不同的值实现和"darker"类似的效果。</li> </ul> <h2 id="参见">参见</h2> <ul> <li>接口定义,{{domxref("CanvasRenderingContext2D")}}</li> <li>{{domxref("CanvasRenderingContext2D.globalAlpha")}}</li> </ul>