feat(gfx): per-plant flora size, placement & tint variation (#675)

[marceld23]

Summary

All flora of a species rendered identically — solid flora (cactus/crystal/mushroom/...) stamped the same full-cell shape for every individual, and cross-billboard plants sat dead-centre on the grid with one fixed rosette orientation, their per-cell triangular jitter averaging back to a uniform carpet at viewing distance.

Everything below is client-only (ChunkMesher.cs, BlockTextureAtlas.cs), derived from pure world-position hashes: deterministic across clients and remeshes, zero protocol/save changes, applies to existing worlds. The block footprint stays exactly one cell.

• A — Solid flora scale + squash: per-column bell x rare outliers (~0.45..1.0 overall) plus an independent height-vs-radius squash; shrink-only, anchored at the cell-floor centre. AddShapedBlock gained optional sizeXZ/sizeY and scales face coords BEFORE emission, so normals/tangents derive from final geometry and the collider (same verts) matches the visual. Player-built shapes pass 1/1 and stay exact.
• B — De-grid: per-plant XZ offset (+/-0.13; AddCrossPlant re-clamps the rosette half-width by the offset magnitude so the floor line stays inside the cell) + rosette spin (+/-30 deg). Keyed per COLUMN (wy = 0) so stacked kelp/vine strands stay one straight, consistently-rotated strand.
• C — Visible distribution: FloraScale blends the fine per-cell bell 50/50 with a coarse 8x8-cell patch hash (meadows form patches of tall and short growth — the scale the eye actually registers); FloraOutlier adds ~5 % giants (x1.4-1.6) and ~8 % runts (x0.5-0.65), keyed per column so an outlier is outsized in every dimension. Torches stay fully exempt.
• D — Tint jitter: +/-8 % per-column brightness wobble on the species tint, gated to flora_* keys (tree leaves/logs untouched) and kept small so species identity incl. toxic-colour recognition stays readable.
• E — Flora variant tiles: the atlas variant mechanism (previously 8 ground blocks) now also paints 2 silhouette-aware variants for 8 signature flora species — variant A sparser/darker (erodes ~40 % of cutout-alpha BOUNDARY pixels; skipped for opaque solid-flora tiles where a zeroed pixel would render black), variant B lighter/warmer. 16 more of the 256 atlas slots (~150 used); flora slots fill AFTER the ground ones so long-shipped variant slot positions are unchanged, with the same graceful capacity guard.

Verification

• dotnet build -c Release: 0 warnings.
• Non-Slow test suite: 1343 server + 147 client passed, 0 failed.
• Local Unity Windows player build from this branch: succeeded (client/Assets changed).

closes #675

🤖 Generated with Claude Code