Züge fahren flüssig statt zu springen

Server liefert zusätzlich die Position in 10 s, der Browser
interpoliert dazwischen (~15 fps).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X48pE4bzjHej8w9HyZXCjb

trainpulse/server.py

@@ -19,6 +19,7 @@ from . import realtime
 from .feed import TZ, Feed
 
 log = logging.getLogger("trainpulse")
+AHEAD = 10
 WEB = Path(__file__).resolve().parent.parent / "web"
 
 
@@ -81,8 +82,14 @@ def poll_realtime():
 def compute_positions():
     if not S.feed:
         return
-    feats = S.feed.vehicles(time.time(), S.rt)
-    S.vehicles = json.dumps({"type": "FeatureCollection", "features": feats}, separators=(",", ":")).encode()
+    now = time.time()
+    feats = S.feed.vehicles(now, S.rt)
+    # Position in AHEAD s mitliefern: der Browser fährt die Züge damit flüssig dazwischen
+    ahead = {f["properties"]["id"]: f["geometry"]["coordinates"] for f in S.feed.vehicles(now + AHEAD, S.rt)}
+    for f in feats:
+        f["next"] = ahead.get(f["properties"]["id"])
+    S.vehicles = json.dumps({"type": "FeatureCollection", "ts": now, "ahead": AHEAD, "features": feats},
+                            separators=(",", ":")).encode()
     S.vehicles_gz = gzip.compress(S.vehicles, 5)
     S.count, S.computed_at = len(feats), time.time()
 
@@ -102,7 +109,7 @@ app = FastAPI(lifespan=lifespan, docs_url=None, redoc_url=None)
 
 @app.get("/api/vehicles")
 def vehicles(request: Request):
-    headers = {"Cache-Control": "no-store"}
+    headers = {"Cache-Control": "no-store", "X-Now": str(time.time())}  # für den Uhrenabgleich im Browser
     if "gzip" in request.headers.get("accept-encoding", ""):
         return Response(S.vehicles_gz, media_type="application/json", headers={**headers, "Content-Encoding": "gzip"})
     return Response(S.vehicles, media_type="application/json", headers=headers)