Joining a crew did nothing. The cab was being built by a replicated entervehicle
that the authority posted only when it had no cab of its own - which is exactly
the case that never happens for the second person to board. The host claims a
vehicle, the server builds a cab, and from then on every further claim finds one
already standing over there, posts nothing, and the joining peer waits forever
for a command that is not coming.
A cab is not a shared object. Each participant has their own, with their own
camera and their own view of it, and nothing about it needs to travel. So it is
built locally by whoever needs one: the driver mode does it for the player when
their claim is granted, and the authority does it for itself, because it needs a
cab to address the AI handover commands to. That also stops a cab being created
on every peer for every claimed vehicle, which is what the entervehicle
broadcast was doing.
Who runs a shared train is no longer decided by car numbering. It is whoever
boarded first, and it stays with them: every crew member is stamped with a
session-wide counter when they sit down, and the smallest stamp on the whole
consist owns the physics. Coupling, uncoupling and renumbering do not move it,
and neither does somebody else joining - each handover is a stutter in the ride
of the person who has been driving, and they are the one who would notice it.
The stamps travel with CREW_UPDATE and in the snapshot, because a client works
out ownership for itself and has to arrive at the same answer.
Chat: the key that opens it is now read before imgui gets a look at the input.
Any window holding the keyboard - the lobby, most likely, which is precisely
where a client sits - would swallow it, so on that side the panel could not be
opened at all. The exception is text actually being typed, which is the chat box
itself; escape closes that. A client also logs what it says, so if a line goes
missing it is clear which half of the trip lost it.
Protocol version 6, snapshot version 7.
Three things that turn out to be one thing: a session with people in it needs
to be able to say who they are, and a machine that only referees one should not
have to open a window to do it.
Names. A peer id is what the protocol addresses; "player 4" is no use to anybody
reading a lobby. CLIENT_HELLO carries a requested nickname now, and the server
decides what it actually is: trimmed of control characters and runs of spaces,
capped at 24, and made unique - two people called Marcin are two people and the
lobby has to say which is which. The result goes out as PEER_ROSTER whenever
somebody joins or leaves, and to a joining peer just before its snapshot, so the
crew section resolves to names rather than numbers. The name comes from
multiplayer.nickname in the ini or --nick on the command line, falling back to
the account name and, failing that, to the old numbering. The host is a peer
like any other here too, and registers its own name at startup.
Chat, on the key left of 1. Going up a line carries only its text: who said it
is decided by the connection it arrived on, never by the field in the packet,
which is what stops anybody putting words in anybody's mouth. The server tidies
and caps it, says it, and passes it on - a client waits to hear itself back, so
that everybody sees the conversation in the same order. While the box has the
keyboard imgui swallows the input before the driver mode sees it, so typing "d"
types "d" instead of opening the doors of whatever you are driving; that also
means the key that opened the panel cannot close it, hence escape.
And --nogui. No glfw, no window, no imgui, the null renderer, sound off, log to
the console it was started from, and nobody in a cab - the scenario is left to
its own drivers and this process is a referee rather than a participant. Every
window-dependent path is guarded on an empty window list rather than on a flag
scattered through the code, and the loop is paced at fifty steps a second
because nothing is waiting on a swapchain to slow it down. Chat lines go to the
log, which is what a machine with no window has instead of a chat panel.
eu07.exe -s scenario.scn --host 0.0.0.0:7420 --nogui --nick Dispatcher
Reversing on the host turned the whole set around on the client, and the
locomotive ended up looking like something derailed making its way across the
scenery. Both come from the same place: a routine correction was calling
place_on_track(), which sets the axles from scratch and works from the
vehicle's own idea of which way it faces. That is right for a peer joining with
nothing to go on, and wrong for a train that is already running - the placement
reorients it.
A correction now slides the vehicle along the track it is already on, by the
difference between the two bogie offsets, which is the same operation the
physics performs on every step. When the two sides disagree about which piece
of track the vehicle is on, it is left alone until they agree; guessing there
is what put a locomotive beside the rails. place_on_track() is kept for the one
case it suits, a peer joining the session.
Also:
- taking a seat works with the game paused. The whole thing sat inside the
"has any time passed" branch, so with the world stopped the lobby button
changed the roster and nothing else happened
- the debug panel gets a Network section, shown only in a session: role, peer,
tick, bytes and messages each way with a running rate, two charts of kB/s so
the cost of a session can be read off, how far the worst vehicle is out of
place, and whether the state digest agrees. The separate "network" overlay
window is gone - everything it said lives there now, together with the lobby
and refusal messages that had nowhere to be seen
Until now the server ran the physics of everything and a client re-ran it from
the server's frame times, corrected a few times a second. That is the worst of
both: the client's own train never moved smoothly, its controls answered a
round trip late, and the two copies still sat metres apart between corrections.
Simulation authority now follows the train:
- the first person aboard a train runs its physics on their own machine, and
what they produce is what the rest of the session is told about it. A train
with nobody in it belongs to the host. Every peer works the owner out the
same way, from the crew of its lowest numbered car, so nobody has to be told
- a peer never applies corrections to a train it runs itself. Its own physics
is the authority on it, and overwriting that is precisely what made the
owner's ride stutter
- a client publishes the state of its own trains upstream, ten times a second.
The server takes it, filtered so a peer can only move the trains it is
entitled to move, and passes it on to everybody else in its own stream
- so the picture is: your train is smooth for you and may stutter for the
others; their trains may stutter for you and are smooth for them
Two things follow from it:
- commands for the train you run take effect the moment you press the key
instead of after a trip to the server and back. They are still sent, so
everybody else sees them, and the echo is dropped when it returns
- the client no longer replays the server's frame times out of a jitter buffer.
It runs on its own clock, like the host does, and simply carries out the
commands as they arrive. Playing back somebody else's frame times meant the
world ran at the wrong speed whenever the two machines drew at different
rates, and every buffered frame sat between the player and their controls
Also: the server only sends a frame when it has commands in it, or every tenth
one to carry the tick, instead of one per rendered frame.
The renderer draws nothing at all while simulation::is_ready is false, and that
flag only goes up once the local player's cab is built.
The previous commit made walking into a cab a crew request, so the cab of a
claimed vehicle is created by Crews::reconcile() rather than by the command
itself. reconcile() runs from the network housekeeping, which was gated on
simulation::is_ready - so a host started with -v had its entervehicle turned
into a claim, and then the cab waited for is_ready while is_ready waited for
the cab. Black screen on both ends, since a client whose server never gets
going has nothing to show either.
- the housekeeping now waits for Global.simulation_loaded, which says the world
exists, instead of simulation::is_ready, which says the player has a cab
- in a session, a player with no cab counts as ready: they are an observer in
the lobby, not a game still loading, and the world has to be drawn for them
- entervehicle is only taken as a crew request when the session actually lists
that vehicle; anything else stays an ordinary command, so a scenario that
starts its host in something the roster does not cover still works
First live test showed three things wrong at once.
A client could not take a vehicle. Walking up to a locomotive and pressing the
enter-vehicle key posts entervehicle, which stage 4 classed as a world-wide
command and refused outright ("reserved for the session host"), so the client
never got a cab and every later control command died locally for want of one.
Walking into a cab is a request for a seat, not a world command: the authority
now turns it into a crew claim, for the host through the same path as for a
remote peer, and answers it the way the lobby button is answered.
Nothing but commands was ever replicated. The server sent dt and the commands
it ran, and the client simulated the rest for itself - so a pantograph the host
raised before the client joined, the contents of the memory cells the signalling
reads, brake pressures and switch positions simply never crossed the wire. The
server now streams the authoritative state a few times a second: whatever has
changed since the last one, and the whole of it every so often so a peer heals
from anything it missed. The snapshot carries the vehicle's inputs - line
breaker, battery, converter and compressor permits, pantograph valves, cab,
lights, doors - and lets the receiving peer derive the rest, plus the memory
cells and the switches.
Desync detection demanded that two state digests be equal, on a design where
the client deliberately runs its own physics. They never can be, so it reported
a desync permanently and asked for a resync every five seconds forever, which
fixed nothing because the next step disagreed again. The digest is a log line
now; what is measured instead is how far out of place the routine correction
found us, and a full resync is only asked for when even that is not catching up.
Also: a consist is put back on the rails as a whole or not at all. Correcting
one vehicle while its neighbour stayed put is what was stretching couplers
until they tore - the last test moved six vehicles out of eight, every time.
And the lobby window collapsed to nothing, because its size_max was left at the
-1 default while size_min was set, so imgui was handed a maximum smaller than
the minimum.
Two things were still missing once a session ran for a while: a peer that had
drifted apart from the authority had no way back short of restarting, and a
connection that blinked cost the player their seat and handed their vehicle to
the AI while the other driver was still sitting in it.
- a client that disagrees with the authoritative digest for 120 steps in a row
asks to be put back in line, and the server answers with a fresh snapshot.
There is a cooldown between requests, so a correction that needs a moment to
take hold does not turn into a stream of them
- the server hands out a session token with its hello and remembers it. Present
it again on the next connection and you come back as the same peer, with the
same id
- a lost connection no longer removes the peer from its crews: the seat is held
for a minute. Come back in time and nothing changed; stay away and the seat
is given up properly, handing the vehicle back to the AI only when that
leaves the crew empty and the AI was driving it in the first place
- after applying a snapshot a peer that finds itself on a crew walks into that
cab, which is what makes a reconnect land the player back where they were
- the vehicle roster is sent to a joining peer right before its snapshot, so
the crew section resolves to names instead of waiting for the next broadcast
Joining meant replaying backbuffer.bin from the very first frame of the
session, so the longer a session ran, the longer it took to get in - and the
whole history had to be kept for it.
- network/snapshot: a chunked container with a version of its own. Every
section carries its length, so a peer built before a section existed reads
a newer snapshot and simply walks past what it does not know. Version 1
carries the session (tick, clock, weather, the state of the random engine),
the vehicles (position on the track, speed, direction, controls, brake
pressures, whether the AI is driving) and the crew roster. Switches,
memcells, signals and the event queue are the next sections
- joining is now: handshake -> load the scenario -> CLIENT_READY -> the server
takes a snapshot on the spot and sends it -> the peer goes live. Because the
snapshot is taken at the moment the peer becomes active there is no backlog
to replay at all; the frame by frame catch-up is gone
- the server refuses a peer that loaded a different scenario, with a readable
reason instead of a silent desync
- reconnecting into a session that is already loaded asks for a fresh snapshot
straight away rather than waiting for a loader that will not run again
- a vehicle is only put back on the rails when it really is somewhere else; the
arithmetic that turns the recorded bogie offset back into the nose distance
place_on_track() expects mirrors what that function itself does
- the session log is still written out - it is useful when picking a desync
apart - but nothing depends on replaying it any more
The protocol hung off whatever frame the renderer happened to be drawing, and
the only thing standing in for synchronisation was the sum of every vehicle's
coordinates with a random number added on top - a value that cannot be equal on
two machines and therefore reported a desync on every single step.
- Global.simulation_tick: the authority counts the steps, a client takes the
number from the authoritative frame it is executing. FRAME_INFO and the
command requests carry it, so the network timeline has one unambiguous order
independent of frame rates
- network/statehash: a versioned FNV digest of the gameplay critical state -
vehicle position, speed, direction, brake pipe and cylinder pressure, plus the
clock. Values are quantized so that float noise is not mistaken for drift, and
vehicles are folded in under their own identity and summed, so the digest does
not depend on the order the scenario created them in. Switches, memcells and
the event queue are the next candidates; they go in when stage 7 pins down
what a snapshot contains
- a client compares its own digest against the authoritative one and reports the
drift when it starts and then only now and then, rather than every step; the
overlay says how long it has been out of step and at which tick
- refusing to compare at all when the two builds disagree on the digest layout
EU07_NETWORK_VERSION is now 4.
A vehicle is not owned by one player: two people share a cab, so the session
needs a crew relation rather than an owner field. The server keeps it and is
the only one allowed to change it.
- network/session: vehicle_crew { entity_id, crew, ai_before_claim } and a
crew_registry holding the roster. the host goes through exactly the same
path as a remote peer (claim -> crew -> grant), only without transport
- CLAIM_VEHICLE / CLAIM_GRANTED / CLAIM_DENIED / LEAVE_VEHICLE / CREW_UPDATE;
the server validates the vehicle exists, is present in the scenario and has
room in the crew, and answers a refusal with a reason the lobby shows
- the cab of a claimed vehicle is created by the authority posting the
ordinary replicated entervehicle, so every peer builds it and the vehicle is
never moved. the claiming peer only walks in once the cab appears locally
- AI transitions follow the crew size: 0 -> 1 remembers whether an AI was
really driving and takes the vehicle over, 1 -> 2 and 2 -> 1 change nothing,
1 -> 0 hands the vehicle back but only if there was an AI driver to begin
with. driver mode no longer fires aidriverdisable of its own in multiplayer
- losing a connection removes that peer from every crew it was on; a vehicle
with somebody still on board carries on untouched
- the lobby lists who is on board, offers "join crew" for a vehicle another
player already occupies, and lets a player step off
The AI and cab handling runs as a reconciliation pass rather than as edge
triggered actions, so a request that has not taken effect yet (the cab needs a
frame to appear) is simply repeated, with a cooldown to keep it off the wire.
TTrain::id() numbers cabs with a local counter, in the order each peer happens
to create them, so it cannot address a vehicle across the session. Neither was
there any way for a player to see what is available to drive.
- network/entities: PeerId (the host is peer 1, remote peers are numbered from
2, so it is a participant rather than a special case) and NetworkEntityId,
plus a registry that numbers the drivable vehicles of the loaded scenario in
name order and resolves ids back to TDynamicObject
- the server owns the numbering and publishes it as VEHICLE_LIST - name, crew
occupancy, crew capacity, AI state, availability - on every change and at
least every 120 frames, out of band so it stays out of the replay backbuffer;
a client binds the received ids to its own copy of the scenario by name
- SERVER_HELLO hands the joining peer its PeerId
- a multiplayer lobby listing that roster, with vehicles taken by other players
shown as such rather than hidden; entering one goes through the existing
entervehicle command, the vehicle is never moved
The lobby lives inside the driver mode instead of a mode of its own: the world
has to keep running while somebody is choosing (a client stops consuming the
server's frames the moment its mode is not a command processor), and the same
screen is what a player needs to change vehicles later on.
Crew occupancy is still derived from the presence of a cab instance; the real
crew model, claim handshake and AI takeover follow in stage 3.
