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mbostockmbostock
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Fix a bug in link strength scaling.
There was a bug in the previous fix to increase the stability of link relaxation; the strength of a link would decrease relative to the link degree of the connected nodes. Instead of decreasing link strength, we should instead bias the relaxation so that the lighter node moves more than the heavier node, while preserving the strength of the link.
1 parent cd135d5 commit 864c3e9

4 files changed

Lines changed: 23 additions & 20 deletions

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‎d3.layout.js‎

Lines changed: 10 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -256,6 +256,7 @@ d3.layout.force = function() {
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s, // current source
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t, // current target
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l, // current distance
259+
k, // current force
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x, // x-distance
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y; // y-distance
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@@ -270,30 +271,30 @@ d3.layout.force = function() {
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l = alpha * strengths[i] * ((l = Math.sqrt(l)) - distances[i]) / l;
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x *= l;
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y *= l;
273-
t.x -= x / t.weight;
274-
t.y -= y / t.weight;
275-
s.x += x / s.weight;
276-
s.y += y / s.weight;
274+
t.x -= x * (k = s.weight / (t.weight + s.weight));
275+
t.y -= y * k;
276+
s.x += x * (k = 1 - k);
277+
s.y += y * k;
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}
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}
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// apply gravity forces
281-
var kg = alpha * gravity;
282+
k = alpha * gravity;
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x = size[0] / 2;
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y = size[1] / 2;
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i = -1; while (++i < n) {
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o = nodes[i];
286-
o.x += (x - o.x) * kg;
287-
o.y += (y - o.y) * kg;
287+
o.x += (x - o.x) * k;
288+
o.y += (y - o.y) * k;
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}
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// compute quadtree center of mass
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d3_layout_forceAccumulate(q);
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293294
// apply charge forces
294-
var kc = alpha * charge;
295+
k = alpha * charge;
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i = -1; while (++i < n) {
296-
q.visit(repulse(nodes[i], kc));
297+
q.visit(repulse(nodes[i], k));
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}
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// position verlet integration

‎d3.layout.min.js‎

Lines changed: 1 addition & 1 deletion
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‎examples/force/force.js‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,8 @@ var vis = d3.select("#chart")
99

1010
d3.json("miserables.json", function(json) {
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var force = d3.layout.force()
12-
.charge(-60)
12+
.charge(-120)
13+
.linkDistance(30)
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.nodes(json.nodes)
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.links(json.links)
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.size([w, h])

‎src/layout/force.js‎

Lines changed: 10 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -50,6 +50,7 @@ d3.layout.force = function() {
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s, // current source
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t, // current target
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l, // current distance
53+
k, // current force
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x, // x-distance
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y; // y-distance
5556

@@ -64,30 +65,30 @@ d3.layout.force = function() {
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l = alpha * strengths[i] * ((l = Math.sqrt(l)) - distances[i]) / l;
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x *= l;
6667
y *= l;
67-
t.x -= x / t.weight;
68-
t.y -= y / t.weight;
69-
s.x += x / s.weight;
70-
s.y += y / s.weight;
68+
t.x -= x * (k = s.weight / (t.weight + s.weight));
69+
t.y -= y * k;
70+
s.x += x * (k = 1 - k);
71+
s.y += y * k;
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}
7273
}
7374

7475
// apply gravity forces
75-
var kg = alpha * gravity;
76+
k = alpha * gravity;
7677
x = size[0] / 2;
7778
y = size[1] / 2;
7879
i = -1; while (++i < n) {
7980
o = nodes[i];
80-
o.x += (x - o.x) * kg;
81-
o.y += (y - o.y) * kg;
81+
o.x += (x - o.x) * k;
82+
o.y += (y - o.y) * k;
8283
}
8384

8485
// compute quadtree center of mass
8586
d3_layout_forceAccumulate(q);
8687

8788
// apply charge forces
88-
var kc = alpha * charge;
89+
k = alpha * charge;
8990
i = -1; while (++i < n) {
90-
q.visit(repulse(nodes[i], kc));
91+
q.visit(repulse(nodes[i], k));
9192
}
9293

9394
// position verlet integration

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