vis.js绘图库的一个BUG以及源码修正

1. BUG

1.1 BUG触发情况

　　在使用vis.js绘图时，加入两个节点A和B之间既存在一条从A指向B的边，同时也存在一条从B指向A的边，那么这个绘图库就会崩溃。

1.2 BUG解析

　　vis.js是动态计算两个节点之间位置的，然后将其在页面上展示出来，而在上述介绍的情况下，在计算A和B之间的距离时，代码中会出现除0的BUG，导致程序崩溃。

2. 解决方案

　　源码有3万多行，为了找这个BUG花了一周的时间，最终确定了出问题的函数。

　　在vis.js源码第12258行(版本更新后位置可能不同)，有个_calculateNodeForces()函数，源码如下：

　　

/**
   * Calculate the forces the nodes apply on eachother based on a repulsion field.
   * This field is linearly approximated.
   *
   * @private
   */
  _calculateNodeForces: function () {
    var dx, dy, angle, distance, fx, fy, combinedClusterSize,
      repulsingForce, node1, node2, i, j;

    var nodes = this.calculationNodes;
    var nodeIndices = this.calculationNodeIndices;

    // approximation constants
    var a_base = -2 / 3;
    var b = 4 / 3;

    // repulsing forces between nodes
    var nodeDistance = this.constants.physics.repulsion.nodeDistance;
    var minimumDistance = nodeDistance;

    // we loop from i over all but the last entree in the array
    // j loops from i+1 to the last. This way we do not double count any of the indices, nor i == j
    for (i = 0; i < nodeIndices.length - 1; i++) {
      node1 = nodes[nodeIndices[i]];
      for (j = i + 1; j < nodeIndices.length; j++) {
        node2 = nodes[nodeIndices[j]];
        combinedClusterSize = node1.clusterSize + node2.clusterSize - 2;

        dx = node2.x - node1.x;
        dy = node2.y - node1.y;
        distance = Math.sqrt(dx * dx + dy * dy);

        minimumDistance = (combinedClusterSize == 0) ? nodeDistance : (nodeDistance * (1 + combinedClusterSize * this.constants.clustering.distanceAmplification));
        var a = a_base / minimumDistance;
        if (distance < 2 * minimumDistance) {
          if (distance < 0.5 * minimumDistance) {
            repulsingForce = 1.0;
          }
          else {
            repulsingForce = a * distance + b; // linear approx of  1 / (1 + Math.exp((distance / minimumDistance - 1) * steepness))
          }

          // amplify the repulsion for clusters.
          repulsingForce *= (combinedClusterSize == 0) ? 1 : 1 + combinedClusterSize * this.constants.clustering.forceAmplification;
          repulsingForce = repulsingForce / distance;

          fx = dx * repulsingForce;
          fy = dy * repulsingForce;

          node1.fx -= fx;
          node1.fy -= fy;
          node2.fx += fx;
          node2.fy += fy;
        }
      }
    }
  }
};

　　这里面有个distance变量，已标红，就是这个变量在我们介绍的情况下会为0，然后它又作为一个被除数，所以程序崩溃。

　　修改后的代码如下：

　　

/**
   * Calculate the forces the nodes apply on eachother based on a repulsion field.
   * This field is linearly approximated.
   *
   * @private
   */
  _calculateNodeForces: function () {
    var dx, dy, angle, distance, fx, fy, combinedClusterSize,
      repulsingForce, node1, node2, i, j;

    var nodes = this.calculationNodes;
    var nodeIndices = this.calculationNodeIndices;

    // approximation constants
    var a_base = -2 / 3;
    var b = 4 / 3;

    // repulsing forces between nodes
    var nodeDistance = this.constants.physics.repulsion.nodeDistance;
    var minimumDistance = nodeDistance;

    // we loop from i over all but the last entree in the array
    // j loops from i+1 to the last. This way we do not double count any of the indices, nor i == j
    for (i = 0; i < nodeIndices.length - 1; i++) {
      node1 = nodes[nodeIndices[i]];
      for (j = i + 1; j < nodeIndices.length; j++) {
        node2 = nodes[nodeIndices[j]];
        combinedClusterSize = node1.clusterSize + node2.clusterSize - 2;

        dx = node2.x - node1.x;
        dy = node2.y - node1.y;
        distance = Math.sqrt(dx * dx + dy * dy);
        if(distance == 0){
          distance = 0.001;
        }

        minimumDistance = (combinedClusterSize == 0) ? nodeDistance : (nodeDistance * (1 + combinedClusterSize * this.constants.clustering.distanceAmplification));
        var a = a_base / minimumDistance;
        if (distance < 2 * minimumDistance) {
          if (distance < 0.5 * minimumDistance) {
            repulsingForce = 1.0;
          }
          else {
            repulsingForce = a * distance + b; // linear approx of  1 / (1 + Math.exp((distance / minimumDistance - 1) * steepness))
          }

          // amplify the repulsion for clusters.
          repulsingForce *= (combinedClusterSize == 0) ? 1 : 1 + combinedClusterSize * this.constants.clustering.forceAmplification;
          repulsingForce = repulsingForce / distance;

          fx = dx * repulsingForce;
          fy = dy * repulsingForce;

          node1.fx -= fx;
          node1.fy -= fy;
          node2.fx += fx;
          node2.fy += fy;
        }
      }
    }
  }
};

　　加上一个判断让它不要为0即可。