186 lines
9.3 KiB
Markdown
186 lines
9.3 KiB
Markdown
# Structure port notes — ground truth from the 26.1.2 jar
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Everything below was read out of `versions/26.1.2/server-26.1.2.jar` with
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javap. It is the working map for porting structure piece generation; treat it
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as reference, not as finished code.
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## Placement grid (implemented, see worldgen/structures.go)
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RandomSpreadStructurePlacement.getPotentialStructureChunk:
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regionX = floorDiv(chunkX, spacing)
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regionZ = floorDiv(chunkZ, spacing)
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r = WorldgenRandom(LegacyRandomSource(0))
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r.setLargeFeatureWithSalt(seed, regionX, regionZ, salt)
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span = spacing - separation
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offsetX = spread.evaluate(r, span)
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offsetZ = spread.evaluate(r, span)
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chunk = (regionX*spacing + offsetX, regionZ*spacing + offsetZ)
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RandomSpreadType.evaluate: linear -> nextInt(span); triangular ->
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(nextInt(span)+nextInt(span))/2.
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setLargeFeatureWithSalt(seed, x, z, salt):
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seed' = x*341873128712 + z*132897987541 + seed + salt, setSeed, zero draws.
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applyAdditionalChunkRestrictions runs only when frequency < 1.0f and calls the
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configured reducer shouldGenerate(seed, salt, x, z, frequency):
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- default / probabilityReducer: setLargeFeatureWithSalt(seed, x, z, salt);
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nextFloat() < frequency.
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- legacy_type_1 / legacyPillagerOutpostReducer: regionX=x>>4, regionZ=z>>4;
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setSeed((long)(regionX ^ (regionZ<<4)) ^ seed); nextInt() discarded once;
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return nextInt((int)(1.0f/frequency)) == 0. For 0.2f the bound computes to 4.
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- legacy_type_2 / legacyArbitrarySaltProbabilityReducer:
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setLargeFeatureWithSalt(seed, x, z, **10387320**) — the set's own salt is
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ignored; nextFloat() < frequency. Buried treasure uses this with 0.01.
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- legacy_type_3 / legacyProbabilityReducerWithDouble: setLargeFeatureSeed(seed,
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x, z) (the two-long XOR mix, no salt); nextDouble() < (double)frequency.
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Mineshafts use this with 0.004.
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Verified against the fixture on seed 12345: ruined_portals claims exactly
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chunk (1,0), where the capture carries the portal's obsidian/gold/crying
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obsidian; mineshaft starts land at (-4,1), (-3,10), (4,-1), consistent with
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the deep oak-plank cells crossing chunks (0,0)/(1,0).
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Not wired yet: concentric_rings (strongholds only).
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## Ruined portal (decoded, not yet ported)
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### Seeding chain (ChunkGenerator.createStructures / lambda$createStructures$0)
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Per set per chunk, in order:
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1. Skip if any structure of the set already has a valid start here.
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2. placement.isStructureChunk(state, x, z) must hold (the grid above).
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3. Single-entry sets go straight to tryGenerateStructure with **zero draws**.
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4. Multi-entry sets: `random = WorldgenRandom(Legacy(0));
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random.setLargeFeatureSeed(levelSeed, chunkX, chunkZ)` (the two-long XOR
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mix), then loop:
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- pick = random.nextInt(totalWeight over remaining entries)
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- walk entries subtracting weight; first negative wins;
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- tryGenerateStructure it; on success stop, else REMOVE the entry,
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total -= its weight, and repeat **without reseeding** (the stream keeps
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running).
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5. tryGenerateStructure -> Structure.generate builds its own
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`WorldgenRandom(LegacyRandomSource(0))` seeded with
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setLargeFeatureSeed(seed, chunkX, chunkZ) — that is the `context.random()`
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every findGenerationPoint draw reads from. Biome check happens inside
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generate via the structure's biomes HolderSet against the biome at the
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generation point (position-dependent, after the stub is found).
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### findGenerationPoint, in draw order
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1. Setup selection — skipped entirely (zero draws) when setups.size() <= 1;
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otherwise sum weights, one nextFloat(), walk setups subtracting
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weight/total, take the first that leaves the accumulator negative.
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2. properties.airPocket = sample(nextFloat vs setup.airPocketProbability),
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where sample returns false at p==0, true at p==1, else nextFloat() < p.
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3. Template: nextFloat() < 0.05 picks giant_portal_{1..3}, otherwise
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portal_{1..10} (both arrays exactly these names, one nextInt(len)).
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4. Rotation = Util.getRandom(Rotation.values(), random) -> one nextInt(4)
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over [none, clockwise_90, clockwise_180, counterclockwise_90].
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5. Mirror: nextFloat() < 0.5 -> none, else front_back.
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6. pivot = (size.x/2, 0, size.z/2) (Java truncating division).
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7. box = template.getBoundingBox(chunkOriginBlockPos, rotation, pivot, mirror).
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8. surfaceY = getBaseHeight(box.center.x, box.center.z,
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getHeightMapType(setup.placement)) - 1, where the type is OCEAN_FLOOR_WG
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for on_ocean_floor and WORLD_SURFACE_WG otherwise.
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9. y = findSuitableY(...) below.
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10. Stub position = (chunkOriginX, y, chunkOriginZ). The piece consumer sets
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properties.cold = setup.canBeCold &&
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biomeAt(quart pos).coldEnoughToSnow(pos, seaLevel), then adds one
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RuinedPortalPiece(templateManager, pos, placement, properties, templateId,
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template, rotation, mirror, pivot).
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findSuitableY(random, generator, placement, airPocket, surfaceY, ySpan, box,
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accessor, randomState):
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minCut = accessor.minY + 15
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switch placement:
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in_nether:
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airPocket ? y = randomBetweenInclusive(32, 100)
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: nextFloat() < 0.5 ? randomBetweenInclusive(27, 29)
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: randomBetweenInclusive(29, 100)
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in_mountain: y = getRandomWithinInterval(70, surfaceY - ySpan)
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underground: y = getRandomWithinInterval(minCut, surfaceY - ySpan)
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partly_buried: y = surfaceY + randomBetweenInclusive(2, 8)
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default: y = surfaceY (on_land_surface, on_ocean_floor)
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// settle: sample the four CORNER columns of the box as raw base columns
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corners = [(minX,minZ),(maxX,minZ),(minX,maxZ),(maxX,maxZ)] as NoiseColumn
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type = on_ocean_floor ? OCEAN_FLOOR_WG : WORLD_SURFACE_WG (isOpaque test)
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while y > minCut:
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opaque = 0
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for column in corners:
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if type.isOpaque(column.getBlock(y)):
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opaque++
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if opaque == 3: return y // stops inside the scan
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y--
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return y
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getRandomWithinInterval(r, a, b): a >= b ? b : randomBetweenInclusive(a, b).
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randomBetweenInclusive(r, lo, hi) = lo + nextInt(hi - lo + 1).
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Remaining to read before coding the piece: ~~RuinedPortalPiece.postProcess~~
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(decoded below), StructureTemplate.getBoundingBox is min/max of transformed
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positions, and placeInWorld writes non-air blocks first, air last.
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### RuinedPortalPiece.postProcess, in order
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1. box = template bounding box under the piece settings; skip when the chunk
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box does not contain box.center; encapsulate otherwise.
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2. TemplateStructurePiece.postProcess = template.placeInWorld with the
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settings below (block entities become markers only).
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3. spreadNetherrack(random, level).
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4. addNetherrackDripColumnsBelowPortal(random, level).
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5. If properties.vines || properties.overgrown: for every position of the
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bounding box (betweenClosedStream order): vines -> maybeAddVines, overgrown
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-> maybeAddLeavesAbove.
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makeSettings(mirror, rotation, placement, pos, properties):
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- ignore processor: airPocket ? STRUCTURE_BLOCK : STRUCTURE_AND_AIR — without
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an air pocket template AIR cells are skipped entirely.
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- RuleProcessor rules, first match wins, each test draws from the block's own
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positional Legacy stream (RandomSource.create(Mth.getSeed(x,y,z)), NOT the
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shared random):
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1. gold_block -> air with probability 0.3 (RandomBlockMatchTest:
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state matches && nextFloat() < p)
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2. lava rule: on_ocean_floor -> lava->magma always; cold ->
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lava->netherrack always; otherwise lava->magma at 0.2
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3. if !cold: netherrack -> magma at 0.07
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- BlockAgeProcessor(mossiness): stone_bricks/stone/chiseled_stone_bricks ->
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maybeReplaceFullStoneBlock (nextFloat >= 0.5 bail; then mossiness roll picks
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between [cracked_stone_bricks | stone_brick_stairs(random facing+half)] and
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[mossy_stone_bricks | mossy_stone_brick_stairs]); stairs tag -> bail at
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nextFloat >= 0.5 else mossy stairs or mossy slab roll; slabs/walls ->
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mossy variant when nextFloat < mossiness; obsidian -> crying_obsidian at
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0.15.
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- ProtectedBlockProcessor(FEATURES_CANNOT_REPLACE): skip placement when the
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CURRENT world block is in the tag.
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- LavaSubmergedBlockProcessor: placed blocks sitting in lava become magma.
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- BlackstoneReplaceProcessor appended only when replaceWithBlackstone.
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spreadNetherrack weights (index by manhattan distance + jitter):
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[1,1,1,1,1,1,1,0.9,0.9,0.8,0.7,0.6,0.4,0.2]; jitter =
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nextInt(max(1, 8 - radius/2)) with radius = (xSpan+zSpan)/2; iterate the
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square around the box center +/- 14; for each cell draw
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nextDouble() < weight[idx], surfaceY = getHeight(type)-1 at that column, y2 =
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surfaceY when on_land_surface/on_ocean_floor else min(box.minY, surfaceY),
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require |y2 - box.minY| <= 3, replace only air/obsidian/not-in-tag/not-lava
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(not in nether), then placeNetherrackOrMagma (cold -> netherrack always;
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else nextFloat < 0.07 -> magma else netherrack); overgrown adds leaves above;
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then addNetherrackDripColumn below (up to 8 steps, each continuing while
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nextFloat < 0.5).
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## Fixture markers worth remembering
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Seed 12345, committed fixture chunks (0,0) (1,0) (0,1) (-1,-1):
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- (1,0): ruined portal — obsidian (17,13,3), crying obsidian (21,13,3),
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gold block (19,18,3), chest (17,13,2).
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- (0,0)/(1,0): mineshaft planks/fences near y=-41..-42.
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- (-1,-1): unexplained cobblestone+mossy floor at y=35 under gravel/water with
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two chests nearby — attributed to no replayed feature yet. Candidate leads:
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a dungeon whose placement stream we mismatch, or an ocean ruin whose pieces
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reach across the chunk border.
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