From 4ed6e2e050e0d9f3d2339bf27773a96d06300a98 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philippe=20Rivi=C3=A8re?= <fil@rezo.net>
Date: Fri, 31 Mar 2023 11:13:17 +0200
Subject: [PATCH] fixes #199

---
 src/collide.js       | 14 +++++++++++---
 test/collide-test.js |  5 ++---
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/collide.js b/src/collide.js
index 8ebd8d9..36f4455 100644
--- a/src/collide.js
+++ b/src/collide.js
@@ -26,7 +26,9 @@ export default function(radius) {
         xi,
         yi,
         ri,
-        ri2;
+        ri2,
+        ax,
+        ay;
 
     for (var k = 0; k < iterations; ++k) {
       tree = quadtree(nodes, x, y).visitAfter(prepare);
@@ -36,6 +38,12 @@ export default function(radius) {
         xi = node.x + node.vx;
         yi = node.y + node.vy;
         tree.visit(apply);
+        if (ax) {
+          node.x += ax;
+          node.y += ay;
+          ax = 0;
+          ay = 0;
+        }
       }
     }
 
@@ -47,8 +55,8 @@ export default function(radius) {
               y = yi - data.y - data.vy,
               l = x * x + y * y;
           if (l < r * r) {
-            if (x === 0) x = jiggle(random), l += x * x;
-            if (y === 0) y = jiggle(random), l += y * y;
+            if (x === 0) ax = jiggle(random), l += ax * ax;
+            if (y === 0) ay = jiggle(random), l += ay * ay;
             l = (r - (l = Math.sqrt(l))) / l * strength;
             node.vx += (x *= l) * (r = (rj *= rj) / (ri2 + rj));
             node.vy += (y *= l) * r;
diff --git a/test/collide-test.js b/test/collide-test.js
index 708196a..f9264be 100644
--- a/test/collide-test.js
+++ b/test/collide-test.js
@@ -39,12 +39,11 @@ it("forceCollide jiggles equal positions", () => {
   f.tick();
   assert(a.x !== b.x);
   assert(a.y !== b.y);
-  assert.strictEqual(a.vx, -b.vx);
-  assert.strictEqual(a.vy, -b.vy);
 });
 
 it("forceCollide jiggles in a reproducible way", () => {
   const nodes = Array.from({length:10}, () => ({x: 0, y: 0}));
   forceSimulation().nodes(nodes).force("collide", forceCollide()).stop().tick(50);
-  assertNodeEqual(nodes[0], {x: -5.371433857229194, y: -2.6644608278592576, index: 0, vy: 0, vx: 0});
+  assertNodeEqual(nodes[0], {x: -4.0299664949858, y: -7.540553942916919, index: 0, vy: 0, vx: 0});
+  assertNodeEqual(nodes[9], {x: 4.160131242078688, y: 0.2022776974891026, index: 9, vy: 0, vx: 0});
 });