AoI: line-of-sight filter (don't stream entities through walls) #150

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opened 2026-07-22 16:45:39 +02:00 by marco · 1 comment

marco commented

2026-07-22 16:45:39 +02:00

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Discovered by the PvP-arena design review (#109). The server streams every entity within the AoI Chebyshev radius (PlayersWithin(pos, radius) / InterestManager / InterestDiff) regardless of walls — it filters on distance, not line of sight. So a modified client sees enemy positions through walls and cover, defeating any cover/LoS play (the arena's whole point) and breaking the server-authoritative fairness pillar.

Fix

Add a line-of-sight filter to AoI membership: an observer is only sent an entity it has TileMap.HasLineOfSight to (in addition to being in range). Entering/leaving LoS reconciles like entering/leaving range (spawn/remove). Compatible with the 'broadcasts carry absolute positions' invariant — this is a membership change, not a delta change.

Notes

Keep it single-threaded on the sim (AoI already reconciles per tick).
Tune cost: LoS check only for in-range candidates; friends-scale so N is small.
Interaction with hearing/say (AoI-scoped chat): decide whether chat still carries through walls (probably yes — you hear a shout you don't see). Scope this issue to visual entity reconciliation.

Definition of Done

Base DoD applies.

A player behind a wall/blocking static is not sent to an observer who has no line of sight, even within AoI radius (verifiable by a unit test on the interest reconciliation + a wall).
Entity reappears when LoS is regained; no flicker/dupe.
No regression to in-range, in-LoS reconciliation.

Discovered by the PvP-arena design review (#109). The server streams every entity within the AoI Chebyshev radius (`PlayersWithin(pos, radius)` / `InterestManager` / `InterestDiff`) **regardless of walls** — it filters on distance, not line of sight. So a modified client sees enemy positions **through walls and cover**, defeating any cover/LoS play (the arena's whole point) and breaking the *server-authoritative fairness* pillar. ## Fix Add a **line-of-sight filter to AoI membership**: an observer is only sent an entity it has `TileMap.HasLineOfSight` to (in addition to being in range). Entering/leaving LoS reconciles like entering/leaving range (spawn/remove). Compatible with the 'broadcasts carry absolute positions' invariant — this is a **membership** change, not a delta change. ## Notes - Keep it single-threaded on the sim (AoI already reconciles per tick). - Tune cost: LoS check only for in-range candidates; friends-scale so N is small. - Interaction with hearing/`say` (AoI-scoped chat): decide whether chat still carries through walls (probably yes — you hear a shout you don't see). Scope this issue to **visual** entity reconciliation. ## Definition of Done _Base DoD applies._ - [ ] A player behind a wall/blocking static is **not** sent to an observer who has no line of sight, even within AoI radius (verifiable by a unit test on the interest reconciliation + a wall). - [ ] Entity reappears when LoS is regained; no flicker/dupe. - [ ] No regression to in-range, in-LoS reconciliation.

marco referenced this issue

2026-07-22 16:46:10 +02:00

Author the PvP arena map on the static content system #109

marco commented

2026-07-22 17:17:08 +02:00

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Closing — won't do (wrong feature). Hiding entities out of line-of-sight is:

not UO — UO sends everyone in your radius; cover stops you being hit, it doesn't hide bodies;
bad UX — with tile-by-tile movement + pillars, players would flicker in/out as LoS breaks/regains;
redundant — the arena's cover is already real: attacks (melee range, bolt, archery #111) are LoS-checked server-side, so you can't hit through a wall regardless of what a client knows;
premature anti-cheat — the only gain is denying a modified client positional info, which vision.md explicitly defers ('friends-scale; no anti-abuse machinery until publicly exposed').

Decision: AoI stays = Chebyshev radius (UO-style visibility); cover is enforced by server-side attack-LoS. Revisit only if the game goes public or gains large room maps. Arena design doc corrected to drop this dependency.

Closing — **won't do (wrong feature).** Hiding entities out of line-of-sight is: - **not UO** — UO sends everyone in your radius; cover stops you being *hit*, it doesn't hide bodies; - **bad UX** — with tile-by-tile movement + pillars, players would flicker in/out as LoS breaks/regains; - **redundant** — the arena's cover is already real: attacks (melee range, bolt, archery #111) are LoS-checked **server-side**, so you can't hit through a wall regardless of what a client knows; - **premature anti-cheat** — the only gain is denying a modified client positional info, which `vision.md` explicitly defers ('friends-scale; no anti-abuse machinery until publicly exposed'). Decision: AoI stays = Chebyshev radius (UO-style visibility); cover is enforced by server-side attack-LoS. Revisit only if the game goes public or gains large room maps. Arena design doc corrected to drop this dependency.

marco closed this issue

2026-07-22 17:17:08 +02:00

marco referenced this issue from a pull request that will close it,

2026-07-22 17:25:46 +02:00

refactor(spells): TargetedSpell base owns target+range+LOS validation once #152

marco referenced this issue from a commit

2026-07-22 17:27:53 +02:00

refactor(spells): TargetedSpell base owns target+range+LOS validation once (#152)