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2023-02-28
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import {quadtree} from "d3-quadtree";
import constant from "./constant.js";
import jiggle from "./jiggle.js";
import {x, y} from "./simulation.js";
export default function() {
var nodes,
node,
random,
alpha,
strength = constant(-30),
strengths,
distanceMin2 = 1,
distanceMax2 = Infinity,
theta2 = 0.81;
function force(_) {
var i, n = nodes.length, tree = quadtree(nodes, x, y).visitAfter(accumulate);
for (alpha = _, i = 0; i < n; ++i) node = nodes[i], tree.visit(apply);
}
function initialize() {
if (!nodes) return;
var i, n = nodes.length, node;
strengths = new Array(n);
for (i = 0; i < n; ++i) node = nodes[i], strengths[node.index] = +strength(node, i, nodes);
}
function accumulate(quad) {
var strength = 0, q, c, weight = 0, x, y, i;
// For internal nodes, accumulate forces from child quadrants.
if (quad.length) {
for (x = y = i = 0; i < 4; ++i) {
if ((q = quad[i]) && (c = Math.abs(q.value))) {
strength += q.value, weight += c, x += c * q.x, y += c * q.y;
}
}
quad.x = x / weight;
quad.y = y / weight;
}
// For leaf nodes, accumulate forces from coincident quadrants.
else {
q = quad;
q.x = q.data.x;
q.y = q.data.y;
do strength += strengths[q.data.index];
while (q = q.next);
}
quad.value = strength;
}
function apply(quad, x1, _, x2) {
if (!quad.value) return true;
var x = quad.x - node.x,
y = quad.y - node.y,
w = x2 - x1,
l = x * x + y * y;
// Apply the Barnes-Hut approximation if possible.
// Limit forces for very close nodes; randomize direction if coincident.
if (w * w / theta2 < l) {
if (l < distanceMax2) {
if (x === 0) x = jiggle(random), l += x * x;
if (y === 0) y = jiggle(random), l += y * y;
if (l < distanceMin2) l = Math.sqrt(distanceMin2 * l);
node.vx += x * quad.value * alpha / l;
node.vy += y * quad.value * alpha / l;
}
return true;
}
// Otherwise, process points directly.
else if (quad.length || l >= distanceMax2) return;
// Limit forces for very close nodes; randomize direction if coincident.
if (quad.data !== node || quad.next) {
if (x === 0) x = jiggle(random), l += x * x;
if (y === 0) y = jiggle(random), l += y * y;
if (l < distanceMin2) l = Math.sqrt(distanceMin2 * l);
}
do if (quad.data !== node) {
w = strengths[quad.data.index] * alpha / l;
node.vx += x * w;
node.vy += y * w;
} while (quad = quad.next);
}
force.initialize = function(_nodes, _random) {
nodes = _nodes;
random = _random;
initialize();
};
force.strength = function(_) {
return arguments.length ? (strength = typeof _ === "function" ? _ : constant(+_), initialize(), force) : strength;
};
force.distanceMin = function(_) {
return arguments.length ? (distanceMin2 = _ * _, force) : Math.sqrt(distanceMin2);
};
force.distanceMax = function(_) {
return arguments.length ? (distanceMax2 = _ * _, force) : Math.sqrt(distanceMax2);
};
force.theta = function(_) {
return arguments.length ? (theta2 = _ * _, force) : Math.sqrt(theta2);
};
return force;
}