bedrockAt had two bugs that cancelled into a deterministic, wrong-looking floor.
It took its chunkRand by value, so next() mutated a copy and all four layers
drew the same 32-bit number. The layers were then decided by successive bits of
that one draw, nesting them into a prefix condition instead of scattering them
independently.
Its ramp also ran backwards. The comment claimed d=1 -> 50% decaying upward, but
`keep := 5 - d` requires more bits set the *lower* the layer, giving 1/16 at the
floor and 1/2 four blocks up — bedrock was likelier further from the bottom.
Vanilla ramps probability linearly from 1 at y=-64 to 0 at y=-59 and tests
nextFloat() < probability, which is what it does now.
Only fillLegacySurface reaches this; the normal path lets the surface rule tree
place the floor from the same datapack vertical_gradient rule. Both should agree.
cmd/gendump is new here: a client-free diagnostic that reports biome
distribution, top surface blocks, subsurface banding, deep-layer composition and
an ASCII cross-section, so generator defects can be seen without launching a
client. Its bedrock-band check prints per-layer counts and fails on any air or
water in the floor. On chunk (0,0) at seed 12345 it now reports y=-64 fully
bedrock, 207/154/106/66 thinning above it, and zero air or water.
The same output also shows the missing subsurface banding — grass sits directly
on stone — which is a separate defect in above_preliminary_surface, not fixed
here.
Replaces the biome-blind fillVanillaColumn heuristics with a full
interpreter for the overworld surface_rule tree (already embedded in
overworld.json): block/sequence/condition/bandlands rules plus all 11
condition tests (biome, steep, hole, water, temperature, y_above,
stone_depth, noise_threshold, not, vertical_gradient,
above_preliminary_surface).
- worldgen/blockids.go: name(+Properties)→network-ID table for surface
blocks (grass/sand/terracotta/mycelium/podzol/coarse_dirt/sandstone/
calcite/snow/ice/...), with snowy property variants.
- worldgen/surface.go: rule-tree parser + interpreter + SurfaceContext;
LoadOverworldSurfaceRule caches the seed-independent tree.
- loader.go: OverworldDensity.SurfaceRule() exposes the parsed tree.
- biome_lookup.go: BiomeNameAt returns the biome name for biome tests.
- vanilla.go: samples the 2D climate + biome before column fill, threads
the rule tree and biome name into fillVanillaColumn, and applies it
top-down with stone as the default for non-matching (deeper) blocks.
The above_preliminary_surface gate uses an inclusive bound so the top
solid block reaches the biome dispatch.
- Performance: one per-column RNG and a reused SurfaceContext keep the
overhead to ~+13ms/chunk (71ms vs 58ms baseline), within the gate.
- Chunk stores per-section biome arrays (64 cells/section); flat generators
keep the uniform single-valued fallback.
- New writeBiomePalette uses min 1 bpe and direct at registry width (65 biomes).
- Climate sampler splits 2D axes (sampled once per column) from 3D depth
(per cell), keeping per-cell cost to a single density-function compute.
- Full biome parameter table (surface + underground twins + lush/dripstone/
deep_dark caves) with depth as a true range, not a binary layer.
- fillBiomes3D fills the 1536 cells/chunk in parallel; <0.3ms overhead vs
baseline chunk gen (benchmark-verified).
- Tests: cave-biome resolution, per-cell variation, flat-world regression,
registry-range validity, plus chunk-gen and per-cell benchmarks.
