どのように表示したいかはわかりませんが、私が思いついたアイデアは次のとおりです。
var depth = {}; // here we store node depths
google.visualization.events.addListener(chart, 'ready', function () {
for (var i = 0; i < data.getNumberOfRows(); i++) {
depth[i] = 0; // we iniialize all in 0 depth
}
for (var i = 0; i < data.getNumberOfRows(); i++) { // for each row
var childs = chart.getChildrenIndexes(i); // we check its descendants
for (var child = 0; child < childs.length; child++) {
depth[childs[child]] += depth[i] + 1; // and add the parents depth+1
}
}
console.log(depth) // here we have already all nodes depth
});
google.visualization.events.addListener(chart, 'select', function () {
if (chart.getSelection().length > 0) {
var node_row = chart.getSelection()[0].row;
console.log(depth[node_row]) // now just show the depth of selected node
}
})
chart.draw(data, {
allowHtml: true
});
作業フィドル: http://jsfiddle.net/a2zwqf1r/