in pytheas-core/src/main/resources/js/d3/d3.layout.js [1481:1518]
function apportion(node, previousSibling, ancestor) {
if (previousSibling) {
var vip = node,
vop = node,
vim = previousSibling,
vom = node.parent.children[0],
sip = vip._tree.mod,
sop = vop._tree.mod,
sim = vim._tree.mod,
som = vom._tree.mod,
shift;
while (vim = d3_layout_treeRight(vim), vip = d3_layout_treeLeft(vip), vim && vip) {
vom = d3_layout_treeLeft(vom);
vop = d3_layout_treeRight(vop);
vop._tree.ancestor = node;
shift = vim._tree.prelim + sim - vip._tree.prelim - sip + separation(vim, vip);
if (shift > 0) {
d3_layout_treeMove(d3_layout_treeAncestor(vim, node, ancestor), node, shift);
sip += shift;
sop += shift;
}
sim += vim._tree.mod;
sip += vip._tree.mod;
som += vom._tree.mod;
sop += vop._tree.mod;
}
if (vim && !d3_layout_treeRight(vop)) {
vop._tree.thread = vim;
vop._tree.mod += sim - sop;
}
if (vip && !d3_layout_treeLeft(vom)) {
vom._tree.thread = vip;
vom._tree.mod += sip - som;
ancestor = node;
}
}
return ancestor;
}