如何使用 FabricJS 使多边形对象对鼠标事件做出反应？

WBOY 转载: 2023-08-31 14:37:08 311浏览

我们可以通过创建fabric.Polygon的实例来创建一个Polygon对象。多边形对象的特征可以是由一组连接的直线段组成的任何闭合形状。由于它是 FabricJS 的基本元素之一，因此我们还可以通过应用角度、不透明度等属性轻松自定义它。我们使用 mouseup 和 mousedown 事件来演示如何多边形对象对用户触发的鼠标事件做出反应。

语法

polygon.on(“mouseup”, callbackFunction);
polygon.on(“mousedown”, callbackFunction);

示例 1：显示对象如何响应 mouseup 事件

让我们看一个代码示例，了解触发 mouseup 事件时多边形对象如何反应。当用户释放鼠标左键时，会发生 mouseup 事件。这里，一旦触发 mouseup 事件，描边宽度就会变为 33。

<!DOCTYPE html>
<html>
<head>
   <!-- Adding the Fabric JS Library-->
   <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script>
</head>
<body>
   <h2>Displaying how the object reacts to the mouseup event</h2>
   <p>
      You can select the object and release the left mouse button to see that the stroke width has changed
   </p>
   <canvas id="canvas"></canvas> 
   <script>
      
      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);
     
     // Initiate a polygon instance
      var polygon = new fabric.Polygon(
         [
            { x: 0, y: 0 },
            { x: 0, y: 50 },
            { x: 50, y: 50 },
            { x: 50, y: 0 },
         ],
         {
            left: 100,
            top: 30,
            fill: "red",
            stroke: "blue",
            strokeWidth: 2,
            objectCaching: false,
         }
      );
      
      // Adding it to the canvas
      canvas.add(polygon);
      
      // Using the mouseup event
      polygon.on("mouseup", () => {
         polygon.set("strokeWidth", 33);
         canvas.renderAll();
      });
   </script>
</body>
</html>

示例 2：显示对象如何响应 mousedown 事件

让我们看一个代码示例，了解触发 mousedown 事件时多边形对象如何反应。当用户按下按钮时，会发生 mousedown 事件。在这里，我们可以看到该对象通过将其描边宽度从 33 更改为 2 来响应 mousedown 事件。

<!DOCTYPE html>
<html>
<head>
   <!-- Adding the Fabric JS Library-->
   <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script>
</head>
<body>
   <h2>Displaying how the object reacts to the mousedown event</h2>
   <p>
      You can press the left mouse button to trigger the mousedown event to see that the stroke width has changed
   </p>
   <canvas id="canvas"></canvas>
   <script>
      
      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);
      
      // Initiate a polygon instance
      var polygon = new fabric.Polygon(
         [
            { x: 0, y: 0 },
            { x: 0, y: 50 },
            { x: 50, y: 50 },
            { x: 50, y: 0 },
         ],
         {
            left: 100,
            top: 30,
            fill: "red",
            stroke: "blue",
            strokeWidth: 33,
            objectCaching: false,
         }
      );
      
      // Adding it to the canvas
      canvas.add(polygon);
      
      // Using the mousedown event
      polygon.on("mousedown", () => {
         polygon.set("strokeWidth", 2);
         canvas.renderAll();
      });
   </script>
</body>
</html>