Elevator Mod — Floor Anchor Model

How the Elevator mod (7days/Elevator) tracks floors and the car, and the desync trap fixed on 2026-07-10.

The model

• BoundsMin is both the ground floor's world position and the base for the car's CurrentOffset (car world Y = BoundsMin.y + CurrentOffset).
• Floor offsets are stored as per-floor Rise gaps, chained and expressed relative to the ground floor (OffsetOfFloor(GroundFloor) == 0).
• CurrentOffset is physical truth: the car's blocks are always at BoundsMin + CurrentOffset by construction (persisted every glide step).

The trap (fixed)

ElevatorBoundsEditor.Start seeds the edit box at the car's current position (BoundsMin + CurrentOffset), so a naive Commit that does BoundsMin = box; CurrentOffset = 0 re-anchors floor 1 wherever the car happens to be parked. Re-editing bounds while parked upstairs silently shifted the whole floor stack up — panel says "floor 1" on the building's second story, and the true bottom story becomes unreachable ("already at floor 1").

Rule: re-editing bounds only repositions the car; keep the ground Y (CurrentOffset = box.y - BoundsMin.y; BoundsMin.y unchanged). Only first-time setup pins ground at the box.

Moving the ground floor

The ground floor is movable like any other, but it is the anchor, so moving it is a pure relabel — no blocks move:

• apply the same neighbor Rise updates as any floor move, plus
• BoundsMin.y += delta and CurrentOffset -= delta

Net effect: every other floor and the parked car keep their world heights; only the reference plane moves. Guard with the bounds editor's world-height clamp (1 .. 250 - size.y) and refuse while ElevatorMover.Active (the mover writes CurrentOffset concurrently).

UX: the anchor row must show live feedback (added 2026-07-10)

Because the ground row's relative height is 0 by definition, showing that offset makes the +/- steppers look dead — the number never changes no matter how many times you click (the user reported "can't adjust floor 1 rise after creation" while the code path worked fine). Fix: the ground row's Height field shows the anchor's world Y ("y" + BoundsMin.y) instead of the frozen 0, and every refused adjustment (world-height clamp, 1..MaxRise gap limits, bounds not set) shows a GameManager.ShowTooltip explaining why instead of a silent return.

General UI rule: a stepper that silently no-ops or edits a value the row doesn't display reads as broken. Surface the value that actually changes, and tooltip every refusal.

General lesson

When a data model stores positions relative to an editable anchor, every anchor edit must explicitly choose which side stays fixed in the world — and compensate the other side. Letting the anchor rebase implicitly is how "the panel says floor 1 but I'm on floor 2" bugs happen.