qtree

function buildQTree() {
        if (.4 > viewZoom) qTree = null;
        else {
            var a = Number.POSITIVE_INFINITY,
                b = Number.POSITIVE_INFINITY,
                c = Number.NEGATIVE_INFINITY,
                d = Number.NEGATIVE_INFINITY,
                e = 0;
            for (var i = 0; i < nodelist.length; i++) {
                var node = nodelist[i];
                if (node.shouldRender() && !node.prepareData && 20 < node.size * viewZoom) {
                    e = Math.max(node.size, e);
                    a = Math.min(node.x, a);
                    b = Math.min(node.y, b);
                    c = Math.max(node.x, c);
                    d = Math.max(node.y, d);
                }
            }
            qTree = Quad.init({
                minX: a - (e + 100),
                minY: b - (e + 100),
                maxX: c + (e + 100),
                maxY: d + (e + 100),
                maxChildren: 2,
                maxDepth: 4
            });
            for (i = 0; i < nodelist.length; i++) {
                node = nodelist[i];
                if (node.shouldRender() && !(20 >= node.size * viewZoom)) {
                    for (a = 0; a < node.points.length; ++a) {
                        b = node.points[a].x;
                        c = node.points[a].y;
                        b < nodeX - canvasWidth / 2 / viewZoom || c < nodeY - canvasHeight / 2 / viewZoom || b > nodeX + canvasWidth / 2 / viewZoom || c > nodeY + canvasHeight / 2 / viewZoom || qTree.insert(node.points[a]);
                    }
                }
            }
        }
    }