prevent vertical overlapping of labels in charts

prevent-overlap.js

define(function(require) {

    'use strict';

    var d3 = require('d3');

    /*
     * tries to eliminate vertical label overlappings
     * by slightly moving the labels away from each
     * other
     *
     * @param labels    a D3 selection of labels created with d3.html.labels
     * @param min_y     the lower boundary for y
     * @param max_y     the upper boundary for y
     * @param min_pad   the minimum distance between two labels (default 0)
     */
    return function(nodes, y_key, min_y, max_y, min_dist) {

        if (!min_dist) min_dist = 10;

        var vNodes = []; // virtual labels

        nodes.forEach(function(node) {
            vNodes.push({
                node: node,
                y: node[y_key],
                dy: 0,
                oy: node[y_key],
            });
        });

        var iter = 0;
        (function loop() {
            var overlap = false;
            vNodes.forEach(function(node0, p) {
                vNodes.forEach(function(node1, q) {
                    if (q > p) {
                        var y0 = node0.y,
                            y1 = node1.y,
                            dy, l0up;
                        if (Math.abs(y0 - y1) < min_dist) {
                            overlap = true;
                            dy = (Math.abs(y0 - y1) - min_dist) * 0.35;
                            l0up = y0 < y1;
                            node0.dy += l0up ? dy : -dy;
                            node1.dy -= l0up ? dy : -dy;
                        }
                    }
                });
            });
            if (overlap) {
                vNodes.forEach(function(node) {
                    node.y = Math.min(Math.max(min_y, node.y + node.dy), max_y);
                    node.dy = 0;
                });
            }
            if (overlap && ++iter < 10) loop();
        })();  // end loop()
        vNodes.forEach(function(node, i) {
            node.node[y_key+'_d'] = node.y - node.oy;
            node.node[y_key] = node.y;
        });
    };

});