如何使用 FabricJS 使多边形对象对缩放事件做出反应？

WBOY 转载: 2023-08-29 11:57:06 419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，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 scaling 事件来演示多边形对象如何对缩放做出反应。

语法

polygon.on(“scaling”, callbackFunction);

示例 1：显示对象如何响应缩放事件

让我们看一个代码示例，了解当缩放事件发生时多边形对象如何反应。我们可以通过拖动任何角控件来缩放对象。这里，当对象被缩放时，缩放事件将被连续触发。

<!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 scaling event</h2>
   <p>
      You can scale the polygon object and open the console from dev tools to see the logged output
   </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: 3,
            objectCaching: false,
         }
      );
      
      // Adding it to the canvas
      canvas.add(polygon);
      
      // Using the scaling event
      polygon.on("scaling", () => {
         canvas.renderAll();
         console.log("The object is being scaled");
      });
   </script>
</body>
</html>

示例 2：缩放时更改描边颜色

让我们看一个代码示例，以了解如何在发生缩放事件时更改描边颜色。我们使用 set 方法将多边形的描边颜色设置为“橙色”。因此，当我们缩放对象时，其描边颜色将变为橙色。

<!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>Changing the stroke colour when scaling happens</h2>
   <p>
      You can see that the stroke colour changes when the polygon is scaled
   </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: 500, y: 20 },
            { x: 550, y: 60 },
            { x: 550, y: 200 },
            { x: 350, y: 200 },
            { x: 350, y: 60 },
            { x: 500, y: 20 },
         ],
         {
            fill: "red",
            stroke: "blue",
            strokeWidth: 5,
            objectCaching: false,
            top: 50,
            left: 30,
            scaleX: 0.5,
            scaleY: 0.5
         }
      );

      // Adding it to the canvas
      canvas.add(polygon);

      // Using the scaling event
      polygon.on("scaling", () => {
         polygon.set("stroke", "orange")
         canvas.renderAll();
      });
   </script>
</body>
</html>