binary.js

export default function(parent, x0, y0, x1, y1) {
  var nodes = parent.children,
      i, n = nodes.length,
      sum, sums = new Array(n + 1);

  for (sums[0] = sum = i = 0; i < n; ++i) {
    sums[i + 1] = sum += nodes[i].value;
  }

  partition(0, n, parent.value, x0, y0, x1, y1);

  function partition(i, j, value, x0, y0, x1, y1) {
    if (i >= j - 1) {
      var node = nodes[i];
      node.x0 = x0, node.y0 = y0;
      node.x1 = x1, node.y1 = y1;
      return;
    }

    var valueOffset = sums[i],
        valueTarget = (value / 2) + valueOffset,
        k = i + 1,
        hi = j - 1;

    while (k < hi) {
      var mid = k + hi >>> 1;
      if (sums[mid] < valueTarget) k = mid + 1;
      else hi = mid;
    }

    if ((valueTarget - sums[k - 1]) < (sums[k] - valueTarget) && i + 1 < k) --k;

    var valueLeft = sums[k] - valueOffset,
        valueRight = value - valueLeft;

    if ((x1 - x0) > (y1 - y0)) {
      var xk = (x0 * valueRight + x1 * valueLeft) / value;
      partition(i, k, valueLeft, x0, y0, xk, y1);
      partition(k, j, valueRight, xk, y0, x1, y1);
    } else {
      var yk = (y0 * valueRight + y1 * valueLeft) / value;
      partition(i, k, valueLeft, x0, y0, x1, yk);
      partition(k, j, valueRight, x0, yk, x1, y1);
    }
  }
}