如何使用ELK（Eclipse Layout Kernel）将节点置于同一层级

我之前在用ELK的layered布局做图时也碰到过一模一样的需求，要强制让特定节点处于同一层级，其实用ELK自带的节点层级约束配置就能搞定，核心是用到elk.layered.constraints.nodeLayers这个布局选项。

具体操作步骤： #

• 在根节点的layoutOptions里新增elk.layered.constraints.nodeLayers配置项，它是一个数组，每一个元素对应一组要放在同一层级的节点。
• 每组节点通过nodes数组指定对应的节点ID，ELK会自动把这些节点安排到同一层级，同时尽量保证整体布局的合理性。

修改后的完整JSON配置示例： #

{
  "children": [
    { "id": "42926", "x": 0, "y": 0, "width": 200, "height": 216 },
    { "id": "42930", "x": 0, "y": 0, "width": 200, "height": 48 },
    { "id": "42942", "x": 0, "y": 0, "width": 200, "height": 172 },
    { "id": "42920", "x": 0, "y": 0, "width": 200, "height": 68 },
    { "id": "42945", "x": 0, "y": 0, "width": 200, "height": 48 },
    { "id": "42958", "x": 0, "y": 0, "width": 200, "height": 71 },
    { "id": "43735", "x": 0, "y": 0, "width": 200, "height": 48 },
    { "id": "43719", "x": 0, "y": 0, "width": 200, "height": 164 },
    { "id": "43720", "x": 0, "y": 0, "width": 200, "height": 48 },
    { "id": "43739", "x": 0, "y": 0, "width": 480, "height": 307 },
    { "id": "43742", "x": 0, "y": 0, "width": 200, "height": 68 },
    { "id": "43744", "x": 0, "y": 0, "width": 200, "height": 51 },
    { "id": "42975", "x": 0, "y": 0, "width": 200, "height": 68 },
    { "id": "43015", "x": 0, "y": 0, "width": 200, "height": 88 },
    { "id": "43013", "x": 0, "y": 0, "width": 200, "height": 68 }
  ],
  "edges": [
    { "id": "42920_42926", "source": "42920", "target": "42926" },
    { "id": "42920_42942", "source": "42920", "target": "42942" },
    { "id": "42920_42958", "source": "42920", "target": "42958" },
    { "id": "42920_43719", "source": "42920", "target": "43719" },
    { "id": "42926_42930", "source": "42926", "target": "42930" },
    { "id": "42942_42945", "source": "42942", "target": "42945" },
    { "id": "42958_43735", "source": "42958", "target": "43735" },
    { "id": "43719_43720", "source": "43719", "target": "43720" },
    { "id": "43739_43742", "source": "43739", "target": "43742" },
    { "id": "43739_43013", "source": "43739", "target": "43013" },
    { "id": "43742_43744", "source": "43742", "target": "43744" },
    { "id": "43744_42926", "source": "43744", "target": "42926" },
    { "id": "43744_42942", "source": "43744", "target": "42942" },
    { "id": "43744_42958", "source": "43744", "target": "42958" },
    { "id": "43744_43719", "source": "43744", "target": "43719" },
    { "id": "42975_43739", "source": "42975", "target": "43739" },
    { "id": "43013_43015", "source": "43013", "target": "43015" }
  ],
  "id": "root",
  "layoutOptions": {
    "elk.algorithm": "layered",
    "elk.direction": "DOWN",
    "elk.hierarchyHandling": "INCLUDE_CHILDREN",
    "elk.layered.spacing.edgeNodeBetweenLayers": 40,
    "elk.layered.nodePlacement.bk.fixedAlignment": "BALANCED",
    "elk.layered.constraints.nodeLayers": [
      {
        "nodes": ["42926", "42942"] // 替换为你需要设置同层级的红色节点ID
      }
    ]
  }
}

额外提示： #

如果遇到布局约束冲突（比如节点的边连接关系导致层级安排矛盾），可以给目标节点单独添加elk.layered.constraints.nodeLayerPriority配置，设置一个较高的数值（比如100），提升层级约束的优先级，确保ELK优先满足节点同层级的要求。

内容的提问来源于stack exchange，提问作者omygoodness