0ad6700a07
Classify teleport landblock transitions from the source and destination Position cell IDs instead of render-space coordinates. This keeps same-dungeon death respawns on their resident floor physics while preserving the existing true cross-landblock streaming path. Co-Authored-By: Codex <noreply@openai.com>
115 lines
4.4 KiB
Markdown
115 lines
4.4 KiB
Markdown
# Same-dungeon respawn landblock identity — retail pseudocode
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## Symptom and captured cause
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After `/die` in the starter dungeon, ACE respawned the player in the same cell,
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`0x8C0401AD`. The player stood correctly until the first movement input, then
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lost floor contact and fell through the world.
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The destination update and the player controller both named cell
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`0x8C0401AD`, but acdream reconstructed the source landblock from render-space
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XYZ. The dungeon cell's valid local Y was about `-30.4 m`, so this expression:
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```text
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sourceLbY = streamingCenterY + floor(renderY / 192 m)
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= 4 + floor(-30.4 / 192)
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= 3
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```
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misidentified the source as landblock `(140,3)`. The destination was `(140,4)`,
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so the same-cell respawn entered the cross-landblock branch, removed
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`0x8C04FFFF` from the physics engine, and left the player with no hydrated floor.
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Dungeon EnvCells may have arbitrary negative frame origins. Their XYZ values
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therefore cannot identify an AC landblock.
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## Named retail oracle
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Retail stores cell identity inside every position:
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```c
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// acclient.h:30658-30662
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struct Position : PackObj
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{
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unsigned int objcell_id;
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Frame frame;
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};
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```
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The local-player teleport path preserves that complete value end to end:
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- `SmartBox::TeleportPlayer @ 0x00453910` passes its `Position const*` directly
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to `CPhysicsObj::SetPositionSimple`.
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- `CPhysicsObj::SetPositionSimple @ 0x005162B0` copies that complete `Position`
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into a `SetPositionStruct`, then calls `CPhysicsObj::SetPosition`.
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- `SmartBox::HandleReceivedPosition`'s local-player teleport branch
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(`0x0045415F`–`0x00454168`) passes the received `Position` to
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`SmartBox::TeleportPlayer`; it does not derive a cell from XYZ.
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References:
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- `docs/research/named-retail/acclient.h:30658`
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- `docs/research/named-retail/acclient_2013_pseudo_c.txt:92514`
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- `docs/research/named-retail/acclient_2013_pseudo_c.txt:93013`
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- `docs/research/named-retail/acclient_2013_pseudo_c.txt:284276`
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## Reference-client/server cross-check
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The existing L.3 research traces the same contract through two independent
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implementations:
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- ACE sends death respawn as `GameMessagePlayerTeleport`, immediately followed
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by an `UpdatePosition` whose `PositionPack` contains the destination cell and
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frame (`docs/research/2026-05-04-l3-port/12-hard-teleport-branch.md`,
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sections 7 and 9).
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- The retail packet path unpacks `PositionPack.position` as
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`objcell_id + Frame` and routes that complete value into the hard-teleport
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branch (`docs/research/2026-05-04-l3-port/03-up-routing.md`, sections 0 and 3).
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The repository's old external ACE checkout is no longer present after the
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WorldBuilder extraction, so the checked-in cross-reference research is the
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stable ACE source citation for this change.
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## Faithful pseudocode
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Retail has synchronous cell access and can install the received `Position`
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directly. acdream keeps its asynchronous loading cover, but the identity
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decision must use the same `Position.objcell_id` values:
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```text
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on local player teleport destination(receivedPosition):
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sourceCell = player.currentPosition.objcell_id
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destinationCell = receivedPosition.objcell_id
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if sourceCell is zero:
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# acdream-only pre-placement fallback; no XYZ inference
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sourceLandblock = currentStreamingCenterLandblock
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else:
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sourceLandblock = landblockOf(sourceCell)
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destinationLandblock = landblockOf(destinationCell)
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crossesLandblock = sourceLandblock != destinationLandblock
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if crossesLandblock:
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evict the old streaming-origin physics landblock
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recenter streaming on destinationLandblock
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start the existing destination hydration path
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retain receivedPosition.objcell_id as the pending destination cell
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when the existing readiness gate opens:
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place the player with the complete destination cell + frame
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```
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`landblockOf(cell)` means `(cell & 0xFFFF0000) | 0xFFFF`. At no point does
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the decision divide or floor position coordinates.
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## Conformance cases
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1. Source and destination are both `0x8C0401AD`, while render Y is negative:
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same landblock; do not evict or recenter.
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2. Source and destination are different EnvCells in `0x8C04`:
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same landblock; do not evict or recenter.
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3. Source `0x8C0401AD`, destination `0xA9B40022`:
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cross-landblock; retain the existing recenter/hydration behavior.
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4. Source cell is zero before first placement:
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compare against the current streaming-center ID; never infer from XYZ.
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