如何在 Vega 中实现节点悬停高亮链接效果-js教程-PHP中文网

如何在 Vega 中实现节点悬停高亮链接效果

霞舞

发布： 2025-10-02 19:37:00

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如何在 vega 中实现节点悬停高亮链接效果

本文旨在指导如何在 Vega 可视化库中实现节点悬停时高亮显示相关链接的功能。通过修改 Vega 的信号和 Marks 属性，我们可以动态改变链接的样式，使其在鼠标悬停于节点上时突出显示，从而增强交互性和数据可读性。本文将提供详细的配置步骤和示例代码，帮助您快速实现这一效果。

要在 Vega 中实现节点悬停时高亮显示链接的效果，主要涉及到以下几个步骤：定义信号（Signals）来追踪鼠标悬停状态，以及修改 Marks 的编码（Encode）属性来根据悬停状态改变链接的样式。

1. 定义信号（Signals）

首先，需要在 Vega 规范中定义一个信号，用于追踪当前鼠标悬停的节点。这个信号会在鼠标悬停在节点上时更新为节点的标识符，而在鼠标移开节点时重置为 null。

{
  "name": "active",
  "value": null,
  "on": [
    {"events": "symbol:mouseover", "update": "datum.name"},
    {"events": "mouseover[!event.item]", "update": "null"}
  ]
}

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这段代码定义了一个名为 active 的信号。

name: 信号的名称，这里是 "active"。
value: 信号的初始值，设置为 null。
on: 定义了信号更新的触发条件。
- {"events": "symbol:mouseover", "update": "datum.name"}：当鼠标悬停在 symbol（即节点）上时，将 active 信号更新为当前节点的数据项的 name 属性。
- {"events": "mouseover[!event.item]", "update": "null"}：当鼠标移开节点时，将 active 信号重置为 null。[!event.item] 表示鼠标移开的是当前节点。

2. 修改 Marks 编码（Encode）

接下来，需要修改链接（path）的 Marks 编码属性，使其根据 active 信号的值来改变链接的样式。

{
  "type": "path",
  "from": {"data": "link-data"},
  "interactive": false,
  "encode": {
    "update": {
      "stroke": [
        {
          "test": "datum.source.name === active || datum.target.name === active",
          "value": "firebrick"
        },
        {"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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这段代码修改了链接的 stroke 属性。

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stroke: 定义了链接的颜色。
- {"test": "datum.source.name === active || datum.target.name === active", "value": "firebrick"}：如果链接的源节点或目标节点的 name 属性与 active 信号的值相等（即鼠标悬停在与该链接相关的节点上），则将链接的颜色设置为 firebrick（红色）。
- {"value": "#ccc"}：否则，将链接的颜色设置为 #ccc（浅灰色）。

3. 完整示例

下面是一个完整的 Vega 规范示例，展示了如何实现节点悬停高亮链接的效果。该示例基于力导向图布局，并使用 miserables.json 数据集。

{
  "$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": [
            {
              "test": "datum.source.name === active || datum.target.name === active",
              "value": "firebrick"
            },
            {"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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