Slabbed

Slabbed 0.5.1-alpha.1 for Fabric 1.21.11

The largest update this line has shipped — 116 commits since 0.5.0-beta.8. The placement core was rebuilt around a single idea: a block's height is computed once, when you place it, and then frozen — recorded in the world save itself, immune to anything that happens around it later. Alpha status reflects the size of that rebuild, not its test coverage: 389 gametests plus client-side proofs run green on every build.

⚠️ BACKUP YOUR WORLDS!

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Some blocks will shift down half a block when upgrading an existing pre-0.5.1 world. This may cause unexpected, permanent effects.

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Slabbed now lets a block rest lower in three cases where it previously stayed flush. Blocks placed before this version carry no saved height, so they follow the new rule the first time they load:

• a carpet resting directly on a bottom slab
• powder snow resting directly on a bottom slab
• a top slab resting directly on a bottom slab

Each now sits half a block lower than on beta.8. Nothing is deleted or relocated — the same builds simply render and collide the way they would if placed today. Measured by resolving identical layouts on both versions: three of thirteen legacy layouts differ, all by −0.5, all downward. If a beta.8 build depends on those staying flush, back it up before upgrading.

The core change: placement is permanent

• Every block item placement records its height at placement time, atomically. Where a block lands is where it stays — breaking its support, building next to it, reloading, or restarting changes nothing. This closes the long-standing family of pop/snap bugs at the root instead of case by case. (Enforced by a blocking invariance matrix; support removal, reload and full-restart persistence confirmed live.)
• A lowered placement that qualifies for no anchor still records its height — protection no longer depends on a lucky classification.
• A block placed flat stays flat, whatever kind of block it is; in-place transforms (grass → dirt, crop growth, waterlogging) keep the recorded height; removal clears only the removed block's record.
• Same-item merges (a second candle, sea pickle, snow layer) preserve the cell's recorded height instead of re-deriving it.

Placement accuracy

• Scaffolding works correctly with Slabbed installed (#65): side-click stacking lands on top of the column, placing upward from inside scaffolding no longer creates an invisible untargetable block, and stacking on a lowered column follows the column's real seat.
• Placing into a replaceable cell (grass, ferns, flowers, one-layer snow) no longer records a wrong height a full cell up or down.
• Slab top-edge and corner clicks place on top of the slab instead of deflecting to the side. (Live-confirmed.)
• Clicks on the visible face of a lowered block are accepted at the server's own validation seam, so what you can see and aim at is what the server lets you build against.
• A slab seats on a bottom slab's top face; a slab may lower onto a slab that is itself sunk; a follower can never sink into its own support; followers inherit their support's actual height rather than a guessed constant.
• Seat decisions ask geometry, not block class: a seat is a face rather than a volume, a TOP or DOUBLE slab counts as a seat, "hanging" is judged by whether a block is hanging rather than whether its type could be, and a plain full block on bare Terrain Slabs no longer earns a spurious anchor and snap.

Targeting

• The pick window widened to ±2 blocks with its radius derived from the active depth cap, so lowered blocks stay targetable across the whole supported range.
• Escape hatch: -Dslabbed.offsetRaycast=false restores vanilla picking entirely.

Terrain Slabs compatibility — improved, not complete

• Player-placed Terrain slab heights are preserved exactly, and a Terrain slab placed onto an already-lowered block continues the surface at the same depth. (Live-confirmed with the original Terrain Slabs 3.3.0.)
• Floor objects (torches, levers, repeaters, comparators) seat on Terrain slab surfaces; hanging objects follow Terrain underside planes.
• Terrain-Slabs-owned vegetation and snow get exactly one offset — Terrain Slabs' own — whether the surface underneath is natural or player-placed.
• Carpets follow their support, and potting a flower no longer moves the block above it.

Stability and rendering

• Fixed a client crash while meshing chunks on Terrain-slab-dense terrain. beta.8 guarded one renderer-boundary read; the rest of the resolver could still walk past the region edge on a mesh worker and crash the game on world load. Every resolver read is now bounded, ending the lookup at the region edge. (Reproduced live on a Terrain worldgen world; fix confirmed on the same world.)
• Chunk-seam culling compares real heights instead of booleans, fixing see-through seams on back rows, and its eligibility follows geometry rather than anchor membership.
• Dependent chunk remeshes are coalesced and prioritised, bounded per tick.
• Lever use particles align with the lever's frozen height, joining the earlier torch, candle, brewing-stand and pot particle fixes.

Multiplayer and world data

• Fixed a chunk that could fail to load once it accumulated roughly 2,048 height markers (#38): the sync format now groups positions by chunk section, keeping even a fully dense chunk under the engine's attachment size ceiling — and at the true limit the store declines a new record instead of corrupting the chunk.
• Vanilla redstone wire connections restored on lowered supports (#37).
• Bottom-slab mob proofing restored (#39).
• Loading a pre-0.5.1 world writes nothing into it: old saves stay byte-clean of Slabbed data until you place something new. (Verified at the region-file level.)

Notices, tooling, packaging

• The join notice now describes the build it is on — this version greets you with alpha, not beta — and the wording can no longer drift from the version.
• /slabdy (the height-readout overlay) ships in every build and is off by default; toggle it with /slabdy. Its readout shows cached versus freshly-computed heights for the target and its support.
• Test, recorder and rig tooling never ships: the release jar is gated by a closed-world allowlist, and both jars are scanned for stray content before release.

Known limits

• The supported lowering floor is one full block (−1.0). A deeper range exists behind an explicit per-world opt-in, for development only.
• A custom Terrain Slabs slab placed directly on top of a vanilla slab still does not lower; the reverse works.
• Side-clicking certain legacy lowered slabs (placed before this version, in specific side-by-side arrangements) can silently place nothing. Being traced; a fix will follow.
• #36 (0–1 FPS) did not reproduce in controlled testing against beta.8 and remains open pending reporter follow-up.

Every 1.21.11 Fabric report filed on GitHub

Reports confirmed against Minecraft 1.21.11 Fabric, credited to their reporters. Issues filed against other versions or loaders are tracked separately and are not listed here.

#	What it was about	Reported by	Status
#1	Crash with Create Fly during startup	DavidBlackCN	Fixed — Slabbed-side initialisation case corrected
#6	Chest stayed attached to a shelf above it; breaking the shelf dropped it	s1rnikorigona-cyber	Fixed — closed on reporter confirmation
#9	Some sand blocks visually affected, suspected Terrain Slabs interaction	Kart0	Fixed with the Terrain Slabs compatibility work
#10	World appeared to shift globally above slabs	Errnick-code	Fixed with the Terrain Slabs compatibility work
#23	Missing ambient occlusion on top faces of blocks on slabs	ChaosMakerMLG	Open — chunk-mesh lighting; not attempted this cycle
#24	Invisible side faces on top slabs placed mid-air	ChaosMakerMLG	Fixed — the face-culling check only considered full blocks; widened to slabs
#35	Rain caused screen flashing, then a crash	07Productions	Fixed in beta.8 — a renderer-boundary check used a development-only class name
#36	0–1 FPS after the #35 crash fix	07Productions	Open — did not reproduce against beta.8 under matched conditions; kept open rather than closed on an unreplicated result
#37	Redstone dust connected to every horizontal direction	MrFrederic	Fixed in this release
#38	A chunk could permanently fail to load once its height data grew too large	MrFrederic	Fixed in this release
#57	Slabbed reported to cause a redstone problem	KumuraTo	Open — related piston-circuit stability now has regression coverage; this report awaits a retest
#64	Pots lost vanilla's floating gap	cassanogiuseppe702-sudo	Open by design — flush seating is intentional; an opt-out is planned
#67	Pots "falling" when the block beneath is broken	Leumas257	Open by design — pots need no support in vanilla and Slabbed adds no survival rule; the visible change is the same intentional flush seating as #64

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👾 Changelog written by AI, edited by Peetsa