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使用 Vega 实现节点悬停高亮链接效果

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发布： 2025-10-02 18:47:18

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使用 vega 实现节点悬停高亮链接效果

本文档将指导你如何在 Vega 可视化库中实现节点悬停时高亮显示相关链接的功能。通过监听鼠标事件，动态更新节点的颜色和链接的样式，从而增强交互性和信息展示效果。本文将提供详细的代码示例和步骤说明，帮助你快速掌握该技巧。

实现步骤

要在 Vega 中实现节点悬停高亮链接的效果，主要需要以下几个步骤：

定义信号 (Signals): 创建用于存储当前激活节点信息的信号。
配置节点 (Nodes) 样式: 根据激活节点信号的值，动态改变节点的填充颜色。
配置链接 (Links) 样式: 根据激活节点信号的值，动态改变链接的颜色。

详细代码示例

以下是一个完整的 Vega 规范示例，展示了如何实现节点悬停高亮链接的效果。

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "A node-link diagram with force-directed layout, depicting character co-occurrence in the novel Les Misérables.",
  "width": 700,
  "height": 500,
  "padding": 0,
  "autosize": "none",
  "signals": [
    {"name": "cx", "update": "width / 2"},
    {"name": "cy", "update": "height / 2"},
    {
      "name": "nodeRadius",
      "value": 8,
      "bind": {"input": "range", "min": 1, "max": 50, "step": 1}
    },
    {
      "name": "nodeCharge",
      "value": -30,
      "bind": {"input": "range", "min": -100, "max": 10, "step": 1}
    },
    {
      "name": "linkDistance",
      "value": 30,
      "bind": {"input": "range", "min": 5, "max": 100, "step": 1}
    },
    {"name": "static", "value": true, "bind": {"input": "checkbox"}},
    {
      "description": "State variable for active node fix status.",
      "name": "fix",
      "value": false,
      "on": [
        {
          "events": "symbol:mouseout[!event.buttons], window:mouseup",
          "update": "false"
        },
        {"events": "symbol:mouseover", "update": "fix || true"},
        {
          "events": "[symbol:mousedown, window:mouseup] > window:mousemove!",
          "update": "xy()",
          "force": true
        }
      ]
    },
    {
      "description": "Graph node most recently interacted with.",
      "name": "node",
      "value": null,
      "on": [
        {"events": "symbol:mouseover", "update": "fix === true ? item() : node"}
      ]
    },
    {
      "description": "Flag to restart Force simulation upon data changes.",
      "name": "restart",
      "value": false,
      "on": [{"events": {"signal": "fix"}, "update": "fix && fix.length"}]
    },
    {
      "name": "active",
      "value": null,
      "on": [
        {"events": "symbol:mouseover", "update": "datum.name"},
        {"events": "mouseover[!event.item]", "update": "null"}
      ]
    }
  ],
  "data": [
    {
      "name": "node-data",
      "url": "data/miserables.json",
      "format": {"type": "json", "property": "nodes"}
    },
    {
      "name": "link-data",
      "url": "data/miserables.json",
      "format": {"type": "json", "property": "links"}
    }
  ],
  "scales": [
    {
      "name": "color",
      "type": "ordinal",
      "domain": {"data": "node-data", "field": "group"},
      "range": {"scheme": "category20c"}
    }
  ],
  "marks": [
    {
      "name": "nodes",
      "type": "symbol",
      "zindex": 1,
      "from": {"data": "node-data"},
      "on": [
        {
          "trigger": "fix",
          "modify": "node",
          "values": "fix === true ? {fx: node.x, fy: node.y} : {fx: fix[0], fy: fix[1]}"
        },
        {"trigger": "!fix", "modify": "node", "values": "{fx: null, fy: null}"}
      ],
      "encode": {
        "enter": {"stroke": {"value": "white"}},
        "update": {
          "fill": {
            "signal": "datum.name==active?'yellow': scale('color', datum.group)"
          },
          "size": {"signal": "2 * nodeRadius * nodeRadius"},
          "cursor": {"value": "pointer"}
        }
      },
      "transform": [
        {
          "type": "force",
          "iterations": 300,
          "restart": {"signal": "restart"},
          "static": {"signal": "static"},
          "signal": "force",
          "forces": [
            {"force": "center", "x": {"signal": "cx"}, "y": {"signal": "cy"}},
            {"force": "collide", "radius": {"signal": "nodeRadius"}},
            {"force": "nbody", "strength": {"signal": "nodeCharge"}},
            {
              "force": "link",
              "links": "link-data",
              "distance": {"signal": "linkDistance"}
            }
          ]
        }
      ]
    },
    {
      "type": "path",
      "from": {"data": "link-data"},
      "interactive": false,
      "encode": {
        "update": {"stroke": {"value": "#ccc"}, "strokeWidth": {"value": 0.5}}
      },
      "transform": [
        {
          "type": "linkpath",
          "require": {"signal": "force"},
          "shape": "line",
          "sourceX": "datum.source.x",
          "sourceY": "datum.source.y",
          "targetX": "datum.target.x",
          "targetY": "datum.target.y"
        }
      ]
    }
  ]
}

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代码解释:

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Signals: active 信号用于存储当前鼠标悬停的节点名称。当鼠标悬停在节点上时，active 信号更新为节点的 datum.name；当鼠标移开节点时，active 信号更新为 null。
Nodes - encode - update - fill: 节点的填充颜色根据 active 信号的值动态变化。如果节点的 datum.name 等于 active 信号的值，则填充颜色为 yellow，否则使用颜色比例尺 color 计算出的颜色。
Links - encode - update - stroke: 链接的颜色始终保持为 "#ccc"，没有实现高亮效果。如果需要高亮链接，需要根据 active 信号的值，动态改变链接的颜色。例如，可以添加一个条件判断，如果链接的源节点或目标节点等于 active 信号的值，则将链接的颜色设置为其他颜色。

高亮链接的修改示例

要实现链接高亮，需要修改 path mark 的 encode 部分。以下是一个修改后的示例：

{
  "type": "path",
  "from": {"data": "link-data"},
  "interactive": false,
  "encode": {
    "update": {
      "stroke": [
        {
          "test": "datum.source.name === active || datum.target.name === active",
          "value": "red"
        },
        {"value": "#ccc"}
      ],
      "strokeWidth": {"value": 0.5}
    }
  },
  "transform": [
    {
      "type": "linkpath",
      "require": {"signal": "force"},
      "shape": "line",
      "sourceX": "datum.source.x",
      "sourceY": "datum.source.y",
      "targetX": "datum.target.x",
      "targetY": "datum.target.y"
    }
  ]
}

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修改解释:

Links - encode - update - stroke: 链接的颜色现在根据 active 信号的值动态变化。如果链接的源节点 (datum.source.name) 或目标节点 (datum.target.name) 等于 active 信号的值，则链接的颜色设置为 red，否则保持为 #ccc。