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import constant from "./constant.js";
export default function(radius, x, y) {
var nodes,
strength = constant(0.1),
strengths,
radiuses;
if (typeof radius !== "function") radius = constant(+radius);
if (x == null) x = 0;
if (y == null) y = 0;
function force(alpha) {
for (var i = 0, n = nodes.length; i < n; ++i) {
var node = nodes[i],
dx = node.x - x || 1e-6,
dy = node.y - y || 1e-6,
r = Math.sqrt(dx * dx + dy * dy),
k = (radiuses[i] - r) * strengths[i] * alpha / r;
node.vx += dx * k;
node.vy += dy * k;
}
}
function initialize() {
if (!nodes) return;
var i, n = nodes.length;
strengths = new Array(n);
radiuses = new Array(n);
for (i = 0; i < n; ++i) {
radiuses[i] = +radius(nodes[i], i, nodes);
strengths[i] = isNaN(radiuses[i]) ? 0 : +strength(nodes[i], i, nodes);
}
}
force.initialize = function(_) {
nodes = _, initialize();
};
force.strength = function(_) {
return arguments.length ? (strength = typeof _ === "function" ? _ : constant(+_), initialize(), force) : strength;
};
force.radius = function(_) {
return arguments.length ? (radius = typeof _ === "function" ? _ : constant(+_), initialize(), force) : radius;
};
force.x = function(_) {
return arguments.length ? (x = +_, force) : x;
};
force.y = function(_) {
return arguments.length ? (y = +_, force) : y;
};
return force;
}
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