The water condition asked "is this block at or above sea level", which is only
the same question as vanilla's in an ocean. Vanilla asks how far the block sits
below the water directly above it, and there is now water that is nowhere near
y=63: the aquifer puts pools at their own levels, deep underground and up in the
hills. Against sea level every one of those read as dry stone, and the stone
above them read as lakebed.
waterHeight is already tracked down the column, so the condition becomes the
vanilla one: pass when there is no water above at all, otherwise when
blockY (+ stoneDepthAbove where the rule asks for it) clears
waterHeight + offset + surfaceDepth * multiplier. add_stone_depth was parsed and
then ignored; three rules in the overworld tree set it.
NoWaterAbove replaces a bare math.MinInt so a hand-built context cannot default
to "water at y=0" by leaving the field unset.
Every air block below y=63 was turned into water. That is one line of code and
it cost the entire underground: no dry caves, no lava lakes, no air pockets, a
solid block of water from the sea floor to bedrock.
Vanilla decides fluid per position instead. Aquifer centres sit on a jittered
16x12x16 grid; each gets a fluid level and type from the floodedness and spread
noises, with centres near open sky inheriting the sea and buried ones getting a
much lower randomised level or nothing at all. A position takes its nearest
centre's fluid unless the barrier noise raises enough pressure between the two
or three nearest centres to seal it back to stone. Deep centres turn to lava.
Porting it means fixing the order of generation, not just adding a file. Vanilla
resolves stone/water/lava/air during the density pass and only then runs the
surface rules over a finished column; we did it the other way round, which is
what forced the unconditional flood in the first place. fillVanillaColumn now
asks the aquifer per position, and applySurfaceRule walks the finished column
carrying the bookkeeping SurfaceSystem carries: air resets the counters, a fluid
records its water height, and stone gets a depth from the top of its run plus
one from the bottom, found by looking ahead to the next non-stone block below.
That last one fixes stone_depth's ceiling form, which had no bottom-up depth to
work with and was testing the top-down one instead -- fourteen rules in the
overworld tree use it to dress cave roofs. The floor form is unchanged: vanilla
counts from 1 and compares against 1 + offset, we counted from 0 and compared
against offset.
The aquifer grid is built eagerly per chunk rather than lazily, because our
columns fill concurrently; every cell is a pure function of its grid coordinate
and every cell in the computed range gets consulted anyway. Cost is ~0.5% of
chunk generation, most of it absorbed by the shared preliminary-surface cache.
Inland caves go from 100% water to 3.8%, and lava exists for the first time.
cmd/gendump grows a census that would have failed loudly before, and
TestCavesAreDry guards it in the suite.
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.
