"Greedy voxel mesher produces vertical stripes on cliff faces instead of horizontal strata"

A greedy voxel mesher that colours cliff "skirts" (vertical faces) using each column's top cell material shows clashing vertical stripes on sheer walls instead of level horizontal strata bands. Thin single-cell buttes look worst — each column picks a different strata band, creating a picket-fence of alternating colours.

A sheer wall exposes one material per column (the top cell's, typically darkened for fake ambient occlusion). Two common classification techniques that work well on flat ground break on walls:

1. Per-cell white-noise dither hash — tuned for plan-view grain, it varies column-to-column on a wall, so vertically adjacent columns pick different strata bands.
2. Smooth contour-wander — a noise perturbation on band-boundary height (hc = h + noise) that makes iso-lines organic on flat ground also causes column-to-column variation on a sheer face.

Both make the strata-band assignment differ between adjacent columns, producing vertical stripes instead of horizontal bands.

Detect wall cells (cells where the maximum quantized step-delta to a 4-neighbour exceeds a threshold, e.g. >= 3 steps ~ 0.75 m over a 0.2 m cell size) and apply different classification rules on them:

1. Key strata on raw absolute Z bands — set bh = h (no contour wander) so band boundaries stay level across every column on the wall.
2. Neutralise the dither hash — set dh = 0.5 so every feather/stop pick resolves to the same hard band in adjacent columns.
3. Drop smooth patch-driven accents (scree, ice overlays) on walls — they streak vertically instead of blending naturally.

Flat ground keeps the contoured, dithered plan-view wash unchanged.

Independently: keep vertically adjacent strata bands as neighbours in colour space. A warm-tan band next to a saturated-blue band clashes violently even one band apart. Ramp rock colours smoothly (e.g. warm-tan to light-neutral-grey to cool blue-grey) with no large hue or value step between adjacent bands.

True horizontal strata on a single-cell sheer face ultimately requires the mesher to vertically subdivide the skirt and colour each sub-quad by its Z band — a more involved change for a later pass.

The root issue is that plan-view variation techniques (dither, contour-wander) produce column-to-column variation, which reads as horizontal grain on flat ground but vertical grain on walls. By detecting wall geometry and falling back to raw-height classification with no per-column noise, you guarantee that adjacent columns on the same wall resolve to the same strata band at each height — producing the horizontal layering that reads as natural rock strata.