如何使用FabricJS将仅选择的折线分组为单个对象

我们可以通过创建 fabric.Polyline 的实例来创建一个折线对象。折线对象可以由一组连接的直线段组成。由于它是FabricJS的基本元素之一，我们还可以通过应用属性（如角度、不透明度等）来轻松自定义它。要将多个折线对象分组，我们可以使用 toGroup() 方法。

语法

toGroup(): Fabric.Group

示例1：创建一个 fabric.Polyline() 的实例并将其添加到我们的画布上

在查看如何将多个对象分组之前，让我们看一个代码示例，其中我们将一个折线对象添加到我们的画布上。唯一必需的参数是 points 数组，而第二个参数是可选的选项对象。

<!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> Creating an instance of fabric.Polyline() and adding it to our canvas </h2>
   <p>You can see that the polyline object has been added</p>
   <canvas id="canvas"></canvas>
   <script>

      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);

      // Initiating a points array
      var points = [
         { x: 30, y: 50 },
         { x: 0, y: 0 },
         { x: 60, y: 0 },
      ];

      // Initiating a polyline object
      var polyline = new fabric.Polyline(points, {
         left: 100,
         top: 40,
         fill: "white",
         strokeWidth: 4,
         stroke: "green",
      });

      // Adding it to the canvas
      canvas.add(polyline);
   </script>
</body>
</html>

示例2：一键分组选择的折线

在这个示例中，我们将有一个按钮，点击该按钮时，选择的折线将被分组为一个单独的对象。因此，移动该对象将移动所有已分组的折线，并且在调整大小或倾斜时行为像一个单一的对象。

我们将创建一个函数，用于获取画布中所有选择的对象，并将它们分组为一个单独的对象。

<!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>Grouping only selected Polyline objects using one click</h2>
    Select the polylines by dragging on required area and click on the`Group` Button to group all the selected Polyline objects in the canvas 
   <canvas id="canvas"></canvas>
   <button type="button" onclick="group()">Group</button>
   <script>

      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);

      // Initiate a Polyline object
      var polyLine1 = new fabric.Polyline([
         { x: 500, y: 200 },
         { x: 550, y: 60 },
         { x: 350, y: 100 },
      ], {
         stroke: "green",
         fill: "white",
         strokeWidth: 5,
      });

      // Initiate another Polyline object
      var polyLine2 = new fabric.Polyline([
         { x: 300, y: 100 },
         { x: 150, y: 60 },
         { x: 250, y: 10 },
      ], {
         stroke: "green",
         fill: "white",
         strokeWidth: 5,
      });

      // Initiate another Polyline object
      var polyLine3 = new fabric.Polyline([
         { x: 400, y: 200 },
         { x: 250, y: 160 },
         { x: 150, y: 200 },
      ], {
         stroke: "green",
         fill: "white",
         strokeWidth: 5,
      });

      // Add them to the canvas instance
      canvas.add(polyLine1);
      canvas.add(polyLine2);
      canvas.add(polyLine3);

      // Function to group the selected polyline objects into single object
      function group() {
         canvas.getActiveObject().toGroup();
      }
   </script>
</body>
</html>