Link force add end condition

src/link.js

@@ -13,11 +13,22 @@ export default function() {
       distance = constant(30),
       distances = [],
       nodes,
+      stableVelocity = 0,
+      stableVeloHandler = null,
       iterations = 1;
 
   function force(alpha) {
+    let n = nodes.length;
+    // Cache old velocity for comparison later
+    if (stableVeloHandler!==null && stableVelocity>=0) {
+      for (let i = n-1, node; i>=0; i--) {
+        node = nodes[i];
+        node.oldvx = node.vx;
+        node.oldvy = node.vy;
+      }
+    }
     // Each iteration in a tick
-    for (var k = 0, n = nodes.length, source, target, i, j, x, y, l; k < iterations; ++k) {
+    for (var k = 0, source, target, i, j, x, y, l; k < iterations; ++k) {
       // For each link
       for (i = 1; i < n; i++) for (j = 0; j < i; j++) {
         // jiggle so l won't be zero and divide by zero error after this
@@ -34,6 +45,20 @@ export default function() {
         source.vy += y;
       }
     }
+
+    // Calculate velocity changes, aka force applied.
+    if (stableVeloHandler!==null && stableVelocity>=0) {
+      let velocityDiff = 0;
+      for (let i = n-1, node; i>=0; i--) {
+        node = nodes[i];
+        velocityDiff += Math.abs(Math.hypot(node.vx-node.oldvx, node.vy-node.oldvy));
+      }
+      velocityDiff /= n*(n-1);
+
+      if(velocityDiff<stableVelocity){
+        stableVeloHandler();
+      }
+    }
   }
 
   function initialize() {
@@ -65,5 +90,12 @@ export default function() {
     return arguments.length ? (distance = typeof _ === "function" ? _ : constant(+_), initializeDistance(), force) : distance;
   };
 
+  force.onStableVelo = function (_) {
+    return arguments.length ? (stableVeloHandler = _, force) : stableVeloHandler;
+  };
+
+  force.stableVelocity = function (_) {
+    return arguments.length ? (stableVelocity = _, force) : stableVelocity;
+  };
   return force;
 }