在给定x坐标的情况下,沿SVG路径获得点的y坐标

Question

我正在使用raphael.js绘制一个简单的SVG线图,如下所示:

当用户将鼠标悬停的图表中,Id喜欢显示酥料饼的指向在所述线X光标位置,并在ÿ位置,其中线是针对X像这样的位置:

我需要获取路径并找到给定X坐标的Y坐标.

Answer 1

基于@Duopixel的D3解决方案，我使用DOM API在纯JavaScript中编写了以下函数供自己使用：

function findY(path, x) {
  var pathLength = path.getTotalLength()
  var start = 0
  var end = pathLength
  var target = (start + end) / 2

  // Ensure that x is within the range of the path
  x = Math.max(x, path.getPointAtLength(0).x)
  x = Math.min(x, path.getPointAtLength(pathLength).x)

  // Walk along the path using binary search 
  // to locate the point with the supplied x value
  while (target >= start && target <= pathLength) {
    var pos = path.getPointAtLength(target)

    // use a threshold instead of strict equality 
    // to handle javascript floating point precision
    if (Math.abs(pos.x - x) < 0.001) {
      return pos.y
    } else if (pos.x > x) {
      end = target
    } else {
      start = target
    }
    target = (start + end) / 2
  }
}