FabricJS 如何将仅选定的Polylines分组到一个对象中

我们可以通过创建一个 fabric.Polyline 的实例来创建一个Polyline对象。一个折线对象可以由一组连接的直线段来描述。由于它是FabricJS的基本元素之一，我们也可以通过应用角度、不透明度等属性来轻松定制它。对于多个折线对象的分组，我们可以使用 toGroup() 方法。

语法

toGroup(): Fabric.Group

例子1：创建 fabric.Polyline() 的实例并将其添加到画布上

在看到我们如何将多个对象组合成一个对象之前，让我们看看如何将多段线对象添加到我们的画布上的代码示例。唯一需要的参数是点数数组，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>

例子2：只用一次点击就能将选定的多段线分组

在这个例子中，我们将有一个按钮，点击这个按钮，被选中的多段线将被分组为一个单一的对象。因此，移动该对象将移动所有分组的多段线，当你调整大小或倾斜时，它将表现为一个单一的对象。

我们将创建一个函数来获取画布中所有被选中的对象并将它们分组为一个单一的对象。

<!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>