Every land column was one block of grass sitting straight on stone. No dirt
under grass, no sandstone under sand, nothing. Two stubs did it together:
above_preliminary_surface compared blockY against the column's actual top block,
so of every position in the column exactly one passed -- and the entire
biome-specific half of the surface rule tree hangs under that condition.
Vanilla compares against a minimum surface level: the preliminary surface level
sampled at the four corners of the 16-block cell, bilinearly interpolated, plus
the surface depth less 8. That is about twenty blocks of reach on ordinary
terrain, which is what the biome subtree is written against.
Surface depth was hardcoded to 0. Vanilla is surfaceNoise*2.75 + 3 with a
per-column jitter, so it comes out around three; it sets how thick the band is
and feeds every add_surface_depth term in the tree. Zero collapsed them all.
Also samples surface_secondary, so stone_depth's secondary_depth_range widens
its band instead of being parsed and dropped.
Grass columns now read grass, two to four dirt, stone -- the histogram over 256
columns is {2: 223, 3: 33}, against vanilla's 2..4. gendump prints it and fails
if the band collapses again; TestGrassColumnsHaveDirt guards it in the suite.
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.
chunkAt prefers the store over the generator, and nothing invalidated a stored
chunk when the generator changed. Combined with four region files committed to
the repo, the chunks around spawn were frozen output from an older generator:
worldgen fixes looked like they did nothing in exactly the area you land in when
you join, and a fresh clone inherited that world.
Chunks now carry a RegionIOGeneratorVersion stamp, written on save and checked on
load; a mismatch returns ErrChunkNotFound so the caller regenerates. Chunks
written before the stamp existed have no tag, decode as 0, and are invalidated
the same way. Bump the constant in any commit that changes generator output.
This is deliberately per-chunk and deliberately quiet. The world metadata file
already guards the seed, where a mismatch means two incompatible terrains and
refusing to open is right. A generator change is routine by comparison and should
just regenerate.
world/region/*.mca and chat.md are untracked (left on disk) and /world/ is
gitignored, superseding the narrower /world/regionio-world.json rule, along with
/.refjava/ and root-level session transcripts.
CLAUDE.md covers the parts of working here that README does not: the
no-dependencies rule, the version-stamp rule and why forgetting it looks like a
failed fix, where the vanilla ground truth lives and how to query the jar
directly with unzip and javap, the precedent for dumping runtime constants with a
throwaway Java program, and an honest list of which layers are bit-exact versus
approximated.
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.
Vanilla's SECTION_BIOMES palette strategy switches on the bit count with
`tableswitch {0..3}`: 0 single-valued, 1-3 linear, and everything else falls
through to the global palette. There is no hashmap tier for biomes — that exists
only for block states, whose 0..8 switch we already implement correctly.
We were writing a linear palette all the way up to 7 bits. A section holding 9 or
more distinct biomes therefore went out as a 4-bit indirect container while the
client read it as global: no palette prefix consumed, long array re-read at 7
bits, and every field after it in the chunk payload misaligned. Sections that
straddle the surface and the cave biomes really do carry that many, so this is
reachable in ordinary terrain rather than a corner case.
Checked against the jar rather than recalled: javap -c on Strategy$2 shows the
{0..3} switch with Configuration$Global in the default arm.
The test decodes each container the way the client would and requires it to
consume exactly the bytes we produced, so a misframed container shows up as a
byte count instead of needing a client to notice. Restoring the old threshold
fails the 9-, 20- and 65-biome cases.
The in-memory chunk+frame cache no longer grows unbounded as players
explore. An LRU policy (doubly-linked list + index map, O(1) per op)
evicts least-recently-used chunks when the cache exceeds MaxCachedChunks,
dropping both the chunk and its cached frame. Dirty chunks are skipped
until the autosave flushes them, so no edit is ever lost to eviction.
- world/cache.go: maxChunks field + order/index LRU bookkeeping; touch
(move-to-front) on every chunkAt/Frame/SetBlock hit; evictIfNeeded on
miss; NewCacheWithLimit constructor (0 = unbounded, backward-compat).
Dirty chunks are bumped to MRU and left in place rather than doing
region I/O under the cache mutex.
- server/server.go: Config.MaxCachedChunks (default 1024); New wires it
into NewCacheWithLimit when a world dir is set.
- cmd/regionio/main.go: -maxcache flag.
- Tests: limit cap, LRU ordering (touched chunk survives), both-maps
drop, dirty-keep, reload-on-access, and edits-survive-eviction+reload
(end-to-end via the store).
The world now survives restarts: chunks load from disk (read-through
cache) and player edits persist via async autosave + a final SaveAll on
shutdown. RegionIO finally does region I/O.
- world/regionfile.go: Anvil .mca container — 8192-byte header
(offset + timestamp tables), 4096-byte sectors, zlib chunk records.
- world/compress.go: zlib deflate/inflate for chunk payloads.
- world/store.go: chunk <-> Level-nested NBT (per-section
block_states/biomes palettes, WORLD_SURFACE heightmap, DataVersion
4790, yPos -4) via the existing nbt package; Store opens one
RegionFile per region with proper floor-division coords.
- world/state_names.go: id->name bridge from the embedded blocks.json
report so network int-IDs round-trip through the disk named palette.
- world/encode.go: GetBiome read accessor for serialization.
- world/cache.go: read-through (disk then generation), dirty tracking,
StartAutosave (returns a done channel so the saver exits before
Close), SaveAll, NewCacheWithStore.
- server.go + main.go: Config.WorldDir (default "world"), -world flag,
autosave loop every 30s, SaveAll + store Close on signal.
- Tests: region round-trip/absent/overwrite, chunk NBT round-trip,
end-to-end save-reload, negative chunk coords, autosave persistence.
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.
