在D3中沿路径拖动

Question

在D3中沿路径拖动

3

使用d3和React，我已经画了一条路径。在这条路径上，我有多个圆形，这些圆形只能沿着路径拖动。然而，我的当前实现只在路径上有一个圆圈时（有点）工作。

（在dragStart上它移动到路径上的长度0，而不管位置，在我拖动第二个圆圈时，它始终从上一个圆圈的位置开始）。

我的问题是：如何在d3中沿着路径拖动多个圆圈（或其他东西）？是否有一种方法根据当前圆圈的cx和cy获取路径上的currentLength位置？

var currentLength = 0;

class MyComponent extends Component {

  constructor(props) {
    super(props)
    currentLength = 0;
  }

  componentDidMount() {
    var drag = d3.behavior.drag()
      .on('drag', this.move);

    var g = d3.select(this._base);
    var circle = g.selectAll('circle').data(this.props.data);
    var onEnter = circle.enter();

      onEnter.append('circle')
      .attr({
        r: 10,
        cx: (d) => d.x,
        cy: (d) => d.y
      })
      .style('fill', 'blue')
      .call(drag);
  }

  move(d) {
    currentLength += d3.event.dx + d3.event.dy

    if (currentLength < 0) {
      currentLength = 0
    }

    var pointAtCurrentLength = d3.select('#path').node().getPointAtLength(currentLength)
    this.cx.baseVal.value = pointAtCurrentLength.x;
    this.cy.baseVal.value = pointAtCurrentLength.y;
  }

  render() {
    return <g ref={(c)=>this._base=c}></g>
  }
}

有些类似于这个例子，只是具备可拖动和多个圆圈：http://bl.ocks.org/mbostock/1705868

- mrlarssen

你能用这段代码创建一个JS Fiddle吗？不看它实际运行起来很难调试。我发现的一个问题是，你没有将move绑定到你的类上，所以分配this.cy/this.cx可能不起作用。 - Michael Camden

1个回答

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- Mark · Accepted Answer

这是对此示例的快速修改，使圆可以拖动：

<!DOCTYPE html>
<meta charset="utf-8">
<style>

path {
  fill: none;
  stroke: #000;
  stroke-width: 1.5px;
}

line {
  fill: none;
  stroke: red;
  stroke-width: 1.5px;
}

circle {
  fill: red;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var points = [[600,276],[586,393],[378,388],[589,148],[346,227],[365,108]];

var width = 960,
    height = 500;

var line = d3.svg.line()
    .interpolate("cardinal");
    
var drag = d3.behavior.drag()
    .on("drag", dragged);

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

var path = svg.append("path")
    .datum(points)
    .attr("d", line);

var line = svg.append("line");

var circle = svg.append("circle")
  .attr("transform", "translate(" + points[0] + ")")
  .attr("r", 7)
  .call(drag);
    
svg.append("circle")
  .attr("transform", "translate(" + points[5] + ")")
  .attr("r", 7)
  .call(drag);

function dragged(d) {
  var m = d3.mouse(svg.node()),
    p = closestPoint(path.node(), m);

  d3.select(this)
    .attr("transform", "translate(" + p[0] + "," + p[1] + ")")
}

function closestPoint(pathNode, point) {
  var pathLength = pathNode.getTotalLength(),
      precision = 8,
      best,
      bestLength,
      bestDistance = Infinity;

  // linear scan for coarse approximation
  for (var scan, scanLength = 0, scanDistance; scanLength <= pathLength; scanLength += precision) {
    if ((scanDistance = distance2(scan = pathNode.getPointAtLength(scanLength))) < bestDistance) {
      best = scan, bestLength = scanLength, bestDistance = scanDistance;
    }
  }

  // binary search for precise estimate
  precision /= 2;
  while (precision > 0.5) {
    var before,
        after,
        beforeLength,
        afterLength,
        beforeDistance,
        afterDistance;
    if ((beforeLength = bestLength - precision) >= 0 && (beforeDistance = distance2(before = pathNode.getPointAtLength(beforeLength))) < bestDistance) {
      best = before, bestLength = beforeLength, bestDistance = beforeDistance;
    } else if ((afterLength = bestLength + precision) <= pathLength && (afterDistance = distance2(after = pathNode.getPointAtLength(afterLength))) < bestDistance) {
      best = after, bestLength = afterLength, bestDistance = afterDistance;
    } else {
      precision /= 2;
    }
  }

  best = [best.x, best.y];
  best.distance = Math.sqrt(bestDistance);
  return best;

  function distance2(p) {
    var dx = p.x - point[0],
        dy = p.y - point[1];
    return dx * dx + dy * dy;
  }
}

</script>