helpdocs/density.md and sky-islands example: corrections against 26.3 vanilla data #186

Small corrections to engine/sema/helpdocs/density.md and the sky-islands example, found while checking the helper text against the 26.3 vanilla data and Mojang's snapshot notes.

helpdocs/density.md

1. end_outer_islands says "The End's island terrain: the main island in the middle, and scattered islands beyond 1024 blocks." Since 26.3 Snapshot 6 the function was renamed from end_islands and "no longer computes the density of the main island". Vanilla now builds the main island separately in end/islands.json from distance_to_point (clamp(100 − d, −100, 80) − 8) / 128, sliced at y = 0) and maxes it with end_outer_islands. Suggested text: "The End's outer islands only. The main island is built separately from distance_to_point; see vanilla end/islands."
2. half_negative says "Vanilla uses it to soften cave walls." Vanilla's only use is on the jagged noise inside overworld/sloped_cheese (and the amplified/large-biomes variants): jaggedness * half_negative(noise(jagged, 1500, 0)), which biases mountain peaks upward. Cave walls are not involved.
3. mul says "Vanilla stops computing right where left is 0." The static-range short-circuit existed through 1.21; I could not confirm it survived the 26.3 single-precision rewrite (Snapshot 7). Suggest hedging or dropping the sentence.
4. interpolated could mention the vanilla cells (4, 8 for overworld/nether/caves, 8, 4 for the End, 16, 1 for chunk_surface_level) and that thresholds (range_choice, thin abs tubes) belong outside it, since interpolation blurs a sign change across the cell.
5. noise shift_x/shift_z: "Vanilla uses ShiftA/ShiftB" is right; worth adding that shift_b samples with x and z swapped so the two warps are decorrelated, and that the vanilla files are minecraft:shift_x / minecraft:shift_z, which a pack can reference directly to line up with vanilla coastlines.

examples/sky-islands/terrain.mms

• islands is used as final_density with no Interpolated, so a 3D noise is sampled at every block. Wrapping it (Interpolated(islands, 4, 8) or a Squeeze around that, as vanilla does) is both faster and the pattern the example should teach.
• No Beardifier(); fine for islands, but a one-line comment saying so would stop people copying the omission into overworld-style packs (26.3 no longer adds it implicitly).

Sources

• 26.3 Snapshot 6: https://www.minecraft.net/en-us/article/minecraft-26-3-snapshot-6
• 26.3 Snapshot 4: https://www.minecraft.net/en-us/article/minecraft-26-3-snapshot-4
• Vanilla 26.3 files: https://github.com/misode/mcmeta/tree/26.3-data/data/minecraft/worldgen/density_function

Generated by Claude Code