slabbed-slab-support-helper-contract

name	slabbed-slab-support-helper-contract
description	Define the single shared helper API all slab-support mixins must use.

Slabbed — Slab Support Helper Contract (Single Source of Truth)

Goal

Define a single, stable helper API for determining whether a block state at a position should count as “ground support” for the top face, including slabs.

All mixins must call this helper; no duplicated slab logic inside mixins.

Non-goals

• No per-block hacks inside mixins
• No broad physics overhaul beyond “support on top face”
• No config (hard-coded rules)

Core rule

Treat the top face of:

• bottom slabs (top surface at y+0.5)
• top slabs (top surface at y+1.0)
• double slabs (y+1.0) as valid “ground support” where vanilla expects solid top support.

Strict visuals expected: placements must align to the slab top surface when possible.

Required helper location

Create helper class (when implementing):

• src/main/java/com/slabbed/init/SlabSupport.java

No other class may implement slab-support rules.

Required public API

When implementing, expose only these methods (no extras unless required):

• static boolean isSupportedOnTop(WorldView world, BlockPos pos, BlockState belowState)

  • Meaning: “does the block at pos.down() support something resting on its TOP face?”

• static double topSurfaceYOffset(BlockState belowState)

  • Returns: surface height in block-space:
    • full block / double slab / top slab => 1.0
    • bottom slab => 0.5
    • unsupported => Double.NaN

• static boolean isSlabLike(BlockState state)

  • True for SlabBlock and any other block types we explicitly add later

Behavior rules (must match vanilla expectations)

isSupportedOnTop(...) should return true if:

1. Vanilla already considers it valid top support (full blocks, etc.), OR
2. The below block is a slab (or slab-like) whose top surface exists and is solid enough for the category being tested.

Do NOT automatically treat:

• stairs
• fences
• walls
• trapdoors
• glass panes as support unless a later skill adds them explicitly.

This mod is “Slabbed”, not “All partial blocks”.

Category flags (for later expansion)

If needed later, helper may accept a “support category” enum, but for now:

• implement the generic “top support” notion first
• per-block strictness comes later via additional wrapper methods if unavoidable

Mandatory instrumentation (debug flags)

When implementing, add optional debug logging controlled by:

• -Dslabbed.debugSupport=true

Logs must be:

• one-line
• prefix [SLABBED_SUPPORT]
• include: pos, belowState, computed yOffset, result

No logs by default.

Pass criteria

• All mixins reference SlabSupport instead of duplicating slab checks
• The helper clearly distinguishes bottom vs top slabs
• The helper does not overreach into other partial blocks

Stop conditions

If more than 2 mixins need slightly different “support” semantics:

• do NOT fork logic inside mixins
• extend helper API in a single place and update all call sites