fabic.js Stickman应用》》元素关联设置/拓扑图

需求：在canvas画布上绘制多个圆形，并添加连接线，图形移动，线自动跟随移动。类似于拓扑关系。

查看fabic文档，Stickman火柴人demo完美适应。官网具体代码如下：

(function() {
  var canvas = this.__canvas = new fabric.Canvas('c', { selection: false });
  fabric.Object.prototype.originX = fabric.Object.prototype.originY = 'center';

  function makeCircle(left, top, line1, line2, line3, line4) {
    var c = new fabric.Circle({
      left: left,
      top: top,
      strokeWidth: 5,
      radius: 12,
      fill: '#fff',
      stroke: '#666'
    });
    c.hasControls = c.hasBorders = false;

    c.line1 = line1;
    c.line2 = line2;
    c.line3 = line3;
    c.line4 = line4;

    return c;
  }

  function makeLine(coords) {
    return new fabric.Line(coords, {
      fill: 'red',
      stroke: 'red',
      strokeWidth: 5,
      selectable: false,
      evented: false,
    });
  }

  var line = makeLine([ 250, 125, 250, 175 ]),
      line2 = makeLine([ 250, 175, 250, 250 ]),
      line3 = makeLine([ 250, 250, 300, 350]),
      line4 = makeLine([ 250, 250, 200, 350]),
      line5 = makeLine([ 250, 175, 175, 225 ]),
      line6 = makeLine([ 250, 175, 325, 225 ]);

  canvas.add(line, line2, line3, line4, line5, line6);

  canvas.add(
    makeCircle(line.get('x1'), line.get('y1'), null, line),
    makeCircle(line.get('x2'), line.get('y2'), line, line2, line5, line6),
    makeCircle(line2.get('x2'), line2.get('y2'), line2, line3, line4),
    makeCircle(line3.get('x2'), line3.get('y2'), line3),
    makeCircle(line4.get('x2'), line4.get('y2'), line4),
    makeCircle(line5.get('x2'), line5.get('y2'), line5),
    makeCircle(line6.get('x2'), line6.get('y2'), line6)
  );

  canvas.on('object:moving', function(e) {
    var p = e.target;
    p.line1 && p.line1.set({ 'x2': p.left, 'y2': p.top });
    p.line2 && p.line2.set({ 'x1': p.left, 'y1': p.top });
    p.line3 && p.line3.set({ 'x1': p.left, 'y1': p.top });
    p.line4 && p.line4.set({ 'x1': p.left, 'y1': p.top });
    canvas.renderAll();
  });
})();

我在vue项目中使用，变形如下：

效果如图（随便拖动一点移动，关联线自动跟随）：

分析：最核心代码为set({ 'x2': p.left, 'y2': p.top })，通过为canvas添加元素移动判定canvas.on('object:moving'，根据移动重新设定线段的绘制坐标。

变形使用：（仅为逻辑，请自行编写判定逻辑）

      canvas.on('object:moving', function (e) {
        var p = e.target
        if (....) { /* 判定我移动的元素是点 ，即是移动会改变关联的元素*/
          canvas.forEachObject(function (object) {
           if(....){ /* 定位到关联的线 */
                object.set({ 'x1': p.left, 'y1': p.top })
            }
          })
        }
      })