interaction - 在 Vega 中拖动数据点的鼠标交互

Question

我正在努力更深入地了解 Vega 图中的交互。目前，我想修改 Voronoi example from the documentation这样您就不会添加和删除点，而是拖动现有的点。我的代码如下所示:

{
  "$schema": "https://vega.github.io/schema/vega/v4.json",
  "width": 500,
  "height": 200,
  "autosize": "none",

  "signals": [
   {
      "name": "movePoint",
      "on": [
        {
          "events": "[mousedown, mouseup] > mousemove",
          "update": "{u: round(100*invert('xscale', x()))/100, v: round(100*invert('yscale', y()))/100}"
        }
      ]
    }
  ],

  "data": [
    {
      "name": "table",
      "values": [
        {"u": 0.1, "v": 0.1},
        {"u": 0.9, "v": 0.1},
        {"u": 0.1, "v": 0.9},
        {"u": 0.9, "v": 0.9},
        {"u": 0.5, "v": 0.5}
      ],
      "on": [
        {"trigger": "movePoint", "modify": "movePoint", "values": "{u: movePoint.u, v: movePoint.v}"}
      ]
    }
  ],

  "scales": [
    {
      "name": "xscale",
      "domain": [0, 1],
      "range": "width"
    },
    {
      "name": "yscale",
      "domain": [0, 1],
      "range": "height"
    }
  ],

  "marks": [
    {
      "name": "points",
      "type": "symbol",
      "zindex": 1,
      "from": {"data": "table"},
      "interactive": false,
      "encode": {
        "enter": {
          "fill": {"value": "black"},
          "size": {"value": 36},
          "x": {"scale": "xscale", "field": "u"},
          "y": {"scale": "yscale", "field": "v"}
        }
      }
    },
    {
      "type": "path",
      "from": {"data": "points"},
      "encode": {
        "enter": {
          "stroke": {"value": "firebrick"},
          "fill": {"value": "transparent"}
        }
      },
      "transform": [
        {
          "type": "voronoi",
          "x": "datum.x", "y": "datum.y",
          "size": [{"signal": "width"}, {"signal": "height"}]
        }
      ]
    }
  ]
}

看来信号已经很好了。我使用 Vega 调试 View 对其进行了测试，它似乎可以正常工作:

• 仅当鼠标按下期间发生鼠标移动时信号才会改变
• 信号值位于正确的坐标系中，即数据使用的坐标系，即坐标介于 0 和 1 之间

不起作用的是交互:我无法拖动点，并且数据不会因鼠标交互而改变。我试图将触发器从数据移动到标记，但也没有用。我需要做什么才能拖动点？

Answer 1

我找到了如何为自己做这件事。问题是我使用的信号计算出正确的新坐标，但它不包含被拖来拖去的对象的 ID。我发现为此添加一个单独的信号最简单。因此，我们现在有了“NewPointPosition”(相同的信号，新名称)和“WhichPoint”，而不是一个“MovePoint”信号，其中包含被拖动对象的 ID。可能这可以合并为一个信号，但这样理解起来可能更容易。

我的第一个版本中缺少的另一个重要点是“点”和“路径”标记需要在“编码”中有一个“更新”子句，而不仅仅是一个“输入”子句。否则，数据会发生变化，但可视化不会对此使用react。

工作代码如下所示:

    {
  "$schema": "https://vega.github.io/schema/vega/v4.json",
  "width": 500,
  "height": 200,
  "autosize": "none",

  "signals": [
   {
      "name": "whichPoint",
      "on": [
        {
          "events": "path:click, path:mousemove[event.buttons]{20}",
          "update": "datum.datum"
        }
      ]
    },
   {
      "name": "newPointPosition",
      "on": [
        {
          "events": "path:click, path:mousemove[event.buttons]{20}",
          "update": "{u: invert('xscale', x()), v: invert('yscale', y())}"
        }
      ]
    }
  ],

  "data": [
    {
      "name": "table",
      "values": [
        {"u": 0.1, "v": 0.1},
        {"u": 0.9, "v": 0.1},
        {"u": 0.1, "v": 0.9},
        {"u": 0.9, "v": 0.9},
        {"u": 0.5, "v": 0.5}
      ],
      "on": [
        {"trigger": "whichPoint", "modify": "whichPoint", "values": "{u: newPointPosition.u, v:newPointPosition.v}"}
      ]
    }
  ],

  "scales": [
    {
      "name": "xscale",
      "domain": [0, 1],
      "range": "width"
    },
    {
      "name": "yscale",
      "domain": [0, 1],
      "range": "height"
    }
  ],

  "marks": [
    {
      "name": "points",
      "type": "symbol",
      "zindex": 1,
      "from": {"data": "table"},
      "encode": {
        "enter": {
          "fill": {"value": "black"},
          "size": {"value": 36},
          "x": {"scale": "xscale", "field": "u"},
          "y": {"scale": "yscale", "field": "v"}
        },
        "update": {
          "fill": {"value": "black"},
          "size": {"value": 36},
          "x": {"scale": "xscale", "field": "u"},
          "y": {"scale": "yscale", "field": "v"}
        }
      }
    },
    {
      "type": "path",
      "from": {"data": "points"},
      "encode": {
        "enter": {
          "stroke": {"value": "firebrick"},
          "fill": {"value": "transparent"}
        },
        "update": {
          "stroke": {"value": "firebrick"},
          "fill": {"value": "transparent"}
        }
      },
      "transform": [
        {
          "type": "voronoi",
          "x": "datum.x", "y": "datum.y",
          "size": [{"signal": "width"}, {"signal": "height"}]
        }
      ]
    }
  ]
}