【发布时间】：2025-03-05 06:05:02
【问题描述】：
在 Mike Bostock 的这个块中，当您移动鼠标时，节点会被推开。从示例中的代码来看，我不明白这是怎么回事。
我看到一个节点在生成布局后已从节点数组中删除，其固定属性设置为 true，并且它的位置会根据鼠标移动进行更新，并且在滴答声期间不会对其进行操作。但从来没有任何力量分配给它。
看起来这种力量是神奇地创造出来的或以某种方式推断出来的。这里发生了什么？
var width = 640,
height = 480,
τ = 2 * Math.PI,
gravity = .05;
var sample = poissonDiscSampler(width, height, 30),
nodes = [{x: 0, y: 0}],
s;
while (s = sample()) nodes.push(s);
var force = d3.layout.force()
.size([width, height])
.nodes(nodes.slice())
.gravity(0)
.charge(function(d, i) { return i ? -30 : -3000; })
.on("tick", ticked)
.start();
var voronoi = d3.geom.voronoi()
.x(function(d) { return d.x; })
.y(function(d) { return d.y; });
var root = nodes.shift();
root.fixed = true;
var links = voronoi.links(nodes);
var canvas = d3.select("body").append("canvas")
.attr("width", width)
.attr("height", height)
.on("ontouchstart" in document ? "touchmove" : "mousemove", moved);
var context = canvas.node().getContext("2d");
function moved() {
var p1 = d3.mouse(this);
root.px = p1[0];
root.py = p1[1];
force.resume();
}
function ticked() {
force.resume();
for (var i = 0, n = nodes.length; i < n; ++i) {
var node = nodes[i];
node.y += (node.cy - node.y) * gravity;
node.x += (node.cx - node.x) * gravity;
}
context.clearRect(0, 0, width, height);
context.beginPath();
for (var i = 0, n = links.length; i < n; ++i) {
var link = links[i];
context.moveTo(link.source.x, link.source.y);
context.lineTo(link.target.x, link.target.y);
}
context.lineWidth = 1;
context.strokeStyle = "#bbb";
context.stroke();
context.beginPath();
for (var i = 0, n = nodes.length; i < n; ++i) {
var node = nodes[i];
context.moveTo(node.x, node.y);
context.arc(node.x, node.y, 2, 0, τ);
}
context.lineWidth = 3;
context.strokeStyle = "#fff";
context.stroke();
context.fillStyle = "#000";
context.fill();
}
// Based on https://www.jasondavies.com/poisson-disc/
function poissonDiscSampler(width, height, radius) {
var k = 30, // maximum number of samples before rejection
radius2 = radius * radius,
R = 3 * radius2,
cellSize = radius * Math.SQRT1_2,
gridWidth = Math.ceil(width / cellSize),
gridHeight = Math.ceil(height / cellSize),
grid = new Array(gridWidth * gridHeight),
queue = [],
queueSize = 0,
sampleSize = 0;
return function() {
if (!sampleSize) return sample(Math.random() * width, Math.random() * height);
// Pick a random existing sample and remove it from the queue.
while (queueSize) {
var i = Math.random() * queueSize | 0,
s = queue[i];
// Make a new candidate between [radius, 2 * radius] from the existing sample.
for (var j = 0; j < k; ++j) {
var a = 2 * Math.PI * Math.random(),
r = Math.sqrt(Math.random() * R + radius2),
x = s.x + r * Math.cos(a),
y = s.y + r * Math.sin(a);
// Reject candidates that are outside the allowed extent,
// or closer than 2 * radius to any existing sample.
if (0 <= x && x < width && 0 <= y && y < height && far(x, y)) return sample(x, y);
}
queue[i] = queue[--queueSize];
queue.length = queueSize;
}
};
function far(x, y) {
var i = x / cellSize | 0,
j = y / cellSize | 0,
i0 = Math.max(i - 2, 0),
j0 = Math.max(j - 2, 0),
i1 = Math.min(i + 3, gridWidth),
j1 = Math.min(j + 3, gridHeight);
for (j = j0; j < j1; ++j) {
var o = j * gridWidth;
for (i = i0; i < i1; ++i) {
if (s = grid[o + i]) {
var s,
dx = s.x - x,
dy = s.y - y;
if (dx * dx + dy * dy < radius2) return false;
}
}
}
return true;
}
function sample(x, y) {
var s = {x: x, y: y, cx: x, cy: y};
queue.push(s);
grid[gridWidth * (y / cellSize | 0) + (x / cellSize | 0)] = s;
++sampleSize;
++queueSize;
return s;
}
}<!DOCTYPE html>
<meta charset="utf-8">
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
</body>【问题讨论】：
标签： javascript d3.js data-visualization force-layout