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fix(#192): close login streaming race — gate on a known real position, not session state

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User-reported: logging in at a non-Holtburg position sometimes showed
stabs/scenery floating in the wrong place. Root-caused via a threading/
lifecycle trace, not inference: WorldSession transitions to InWorld
immediately after the login handshake (WorldSession.cs:608) — well
before the player's own spawn CreateObject (which carries their real
position) has arrived over the network. The streaming gate's old
condition (`!IsLiveModeWaitingForLogin || liveInWorld`) opened the
instant InWorld fired, letting the background streaming worker
(LandblockStreamer's dedicated Thread) build real landblocks using
whatever _liveCenterX/Y held at that moment — the Holtburg startup
placeholder, not a "not known yet" sentinel. Landblocks that started
building in that window bake their world offset from that placeholder
at build time; if their build was still in flight when the real spawn
arrived and recentered the world (ForceReloadWindow, which only
unloads already-RESIDENT landblocks), they finished and got applied
anyway — stale-positioned geometry landing wherever the guess put it
relative to whatever streamed in afterward with the corrected center.

Confirmed with the user this wasn't "wrong placeholder, need a better
one" — any placeholder racing against the real answer reproduces the
same bug. The fix removes the race instead: StreamingReadinessGate
.ShouldStream requires an explicit liveCenterKnown flag (true only once
the player's own spawn has been processed) in addition to liveInWorld.
Nothing streams in live mode until the real position is confirmed — no
placeholder value is ever acted on. Preserves the #106 gate-3 fix this
gate originally existed for (auto-entry waits for terrain under the
spawn; terrain streaming must not wait for chase mode in turn, or the
two deadlock) since liveCenterKnown becomes true independently of chase
mode, driven purely by the spawn packet's arrival.

The stricter render gate (GameWindow.cs:9596, hides ALL world geometry
until chase mode engages, no relaxation) already provided a partial
safety net and is unchanged — this fix stops the stale geometry from
ever being built, rather than relying on the render gate to hide it
until the reveal.

Core 2680+2skip / App 741+2skip / UI 425 / Net 385 green.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
Erik 2026-07-09 15:57:43 +02:00
parent 3dcd53cab7
commit fa9aedca0a
3 changed files with 149 additions and 1 deletions
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27
src/AcDream.App/Rendering/GameWindow.cs
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@ -969,6 +969,15 @@ public sealed class GameWindow : IDisposable
private AcDream.Core.Net.WorldSession? _liveSession;
private int _liveCenterX;
private int _liveCenterY;
// #192 (2026-07-09): true once the player's OWN spawn CreateObject has been
// received and processed — i.e. _liveCenterX/Y reflects a real,
// server-confirmed position, not the Holtburg startup placeholder. Gates
// streaming via StreamingReadinessGate.ShouldStream so no landblock is ever
// built around a still-guessed center in live mode. See
// AcDream.Core.World.StreamingReadinessGate for the full mechanism this
// closes (stale-centered geometry built during the InWorld-but-not-yet-
// located window, applied late once its build finished).
private bool _liveCenterKnown;
// Set by the login-spawn recenter (network thread) when the spawn landblock
// differs from the startup streaming center; consumed on the render thread
// in OnUpdateFrame to trigger StreamingController.ForceReloadWindow(). A far
@ -3306,6 +3315,14 @@ public sealed class GameWindow : IDisposable
// object spawns never move the center. Idempotent + thrash-free: a
// re-sent CreateObject for the same spawn landblock leaves the center
// already-equal, so the guard is false on every repeat.
//
// #192: the player's own spawn is the first point we can trust
// _liveCenterX/Y as a REAL position rather than the Holtburg startup
// placeholder — set this unconditionally (even when no recenter is
// needed, e.g. a genuine Holtburg login) so StreamingReadinessGate can
// stop gating streaming on session state alone.
if (spawn.Guid == _playerServerGuid)
_liveCenterKnown = true;
if (spawn.Guid == _playerServerGuid
&& (lbX != _liveCenterX || lbY != _liveCenterY))
{
@ -8281,8 +8298,16 @@ public sealed class GameWindow : IDisposable
// only.
bool liveInWorld = _liveSession is not null
&& _liveSession.CurrentState == AcDream.Core.Net.WorldSession.State.InWorld;
// #192: liveInWorld alone used to be sufficient here — but InWorld fires
// right after the login handshake, before the player's own spawn
// CreateObject (and hence the real center) has arrived. Streaming that
// ran in that gap baked landblock offsets from the still-placeholder
// _liveCenterX/Y (Holtburg), producing stale-positioned geometry applied
// late once its build finished. Require _liveCenterKnown too — see
// AcDream.Core.World.StreamingReadinessGate for the full mechanism.
if (_streamingController is not null && _cameraController is not null
&& (!IsLiveModeWaitingForLogin || liveInWorld))
&& AcDream.Core.World.StreamingReadinessGate.ShouldStream(
LiveModeEnabled, _chaseModeEverEntered, liveInWorld, _liveCenterKnown))
{
int observerCx = _liveCenterX;
int observerCy = _liveCenterY;