Keep trains straight at the terminals

openenv/rail_openenv/web/twin/geo.js

@@ -11,6 +11,7 @@
 export const CANONICAL = { E: "E-8-5a", W: "W-5a-8" };
 const RAMP_SWITCH = 0.03;    // km: zones bounded by a switch, where the two tracks meet
 const RAMP_CROSS = 0.25;     // km: zones that end on double track
+const END_RUN = 20;          // m: the stretch whose direction a route keeps past its ends
 
 export function smoothstep(u) {
   const x = Math.min(1, Math.max(0, u));
@@ -65,12 +66,21 @@ export class Route {
     return kl + (s - sl) / 1000 * (this.dir === "E" ? 1 : -1);
   }
 
-  // [x, y] at distance s (clamped to the route)
+  // [x, y] at distance s. Routes end at the terminals' stop points, so a train standing there reaches past an end by
+  // half its length: past either end the track goes on straight, along its last END_RUN metres. (Clamping folded
+  // those cars back onto the end point.)
   pointAtS(s) {
     const S = this.s;
     const n = S.length;
-    if (s <= 0) return [this.x[0], this.y[0]];
-    if (s >= this.length) return [this.x[n - 1], this.y[n - 1]];
+    if (s < 0 || s > this.length) {
+      const atEnd = s > this.length;
+      const [ex, ey] = atEnd ? [this.x[n - 1], this.y[n - 1]] : [this.x[0], this.y[0]];
+      const [bx, by] = this.pointAtS(atEnd ? Math.max(0, this.length - END_RUN) : Math.min(this.length, END_RUN));
+      const L = Math.hypot(ex - bx, ey - by);
+      if (L < 1e-6) return [ex, ey];
+      const d = atEnd ? s - this.length : -s;
+      return [ex + (ex - bx) / L * d, ey + (ey - by) / L * d];
+    }
     let lo = 0, hi = n - 1;
     while (hi - lo > 1) {
       const mid = (lo + hi) >> 1;