simple vega legend

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "width": 200,
  "height": 200,
  "autosize": "none",

  "signals": [
    {
      "name": "startAngle", "value": 0,
      "bind": {"input": "range", "min": 0, "max": 6.29, "step": 0.01}
    },
    {
      "name": "endAngle", "value": 6.29,
      "bind": {"input": "range", "min": 0, "max": 6.29, "step": 0.01}
    },
    {
      "name": "padAngle", "value": 0,
      "bind": {"input": "range", "min": 0, "max": 0.1}
    },
    {
      "name": "innerRadius", "value": 0,
      "bind": {"input": "range", "min": 0, "max": 90, "step": 1}
    },
    {
      "name": "cornerRadius", "value": 0,
      "bind": {"input": "range", "min": 0, "max": 10, "step": 0.5}
    },
    {
      "name": "sort", "value": false,
      "bind": {"input": "checkbox"}
    }
  ],

  "data": [
    {
      "name": "table",
      "values": [
        {"id": 1, "field": 4},
        {"id": 2, "field": 6},
        {"id": 3, "field": 10},
        {"id": 4, "field": 3},
        {"id": 5, "field": 7},
        {"id": 6, "field": 8}
      ],
      "transform": [
        {
          "type": "pie",
          "field": "field",
          "startAngle": {"signal": "startAngle"},
          "endAngle": {"signal": "endAngle"},
          "sort": {"signal": "sort"}
        }
      ]
    }
  ],

  "scales": [
    {
      "name": "color",
      "type": "ordinal",
      "domain": {"data": "table", "field": "id"},
      "range": {"scheme": "category20"}
    }
  ],

  "marks": [
    {
      "type": "arc",
      "from": {"data": "table"},
      "encode": {
        "enter": {
          "fill": {"scale": "color", "field": "id"},
          "x": {"signal": "width / 2"},
          "y": {"signal": "height / 2"}
        },
        "update": {
          "startAngle": {"field": "startAngle"},
          "endAngle": {"field": "endAngle"},
          "padAngle": {"signal": "padAngle"},
          "innerRadius": {"signal": "innerRadius"},
          "outerRadius": {"signal": "width / 2"},
          "cornerRadius": {"signal": "cornerRadius"}
        }
      }
    }
  ]
}