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我們可以通過創建fabric.Polygon的實例來創建一個Polygon對象。多邊形對象的特征可以是由一組連接的直線段組成的任何閉合形狀。由于它是 FabricJS 的基本元素之一，我們還可以通過應用角度、不透明度等屬性輕松自定義它。我們使用 selected 和 deselected 事件來演示如何使多邊形對象對用戶選擇和取消選擇對象做出反應。

語法

polygon.on("selected", callbackFunction);
polygon.on("deselected", callbackFunction);

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示例 1：顯示對象如何對所選事件做出反應

讓我們看一個代碼示例，了解如何使多邊形對象對 selected 事件做出反應。單擊該對象將觸發執行回調函數的 selected 事件。在本例中，只要我們單擊多邊形對象，其填充顏色就會發生變化并顯示記錄的輸出。

<!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 selected event</h2>
   <p>Select the object to see the event callback function fired</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: "black",
            stroke: "blue",
            strokeWidth: 2,
            objectCaching: false,
         }
      );
      
      // Adding it to the canvas
      canvas.add(polygon);
      
      // Using the selected event
      polygon.on("selected", () => {
         polygon.fill = "blue";
         canvas.renderAll();
         console.log("The polygon object is selected");
      });
   </script>
</body>
</html>

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示例 2：顯示對象如何對取消選擇的事件做出反應

讓我們看一個代碼示例來了解如何使 Polygon 對象對取消選擇事件做出反應。在這里，一旦取消選擇多邊形對象，就會觸發該事件，從而也改變填充顏色。

<!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>Displaying how the object reacts to the deselected event</h2>
   <p>Deselect the object to see the event callback function fired</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: 2,
            objectCaching: false,
         }
      );
      
      // Adding it to the canvas 
      canvas.add(polygon);
      
      // Using the deselected event
      polygon.on("deselected", () => {
         polygon.fill = "black";
         canvas.renderAll();
         console.log("The polygon object is deselected");
      });
   </script>
</body>
</html>

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