ab_stone_bowl

# ab_stone The crater's basalt: coursed into retaining walls where the garden was built, natural everywhere else, under whatever ash is still lying on it. **It declares no textures.** Every mark on it — the courses, the chipped edge of each split block, the vesicular pitting, the ash packed into a joint, the sheen of water on a flat — is computed from world position. So it spends nothing of the material texture budget, its detail has no resolution, and one material carries the 250 m rim wide and an 8 cm macro of a single stone. ## Driven every frame | property | | |---|---| | `wetness` | 0 → 0.78. Darkens the albedo by most of a stop, drops the roughness, and gathers standing water in the low places. Water finds the flats first, and ash that is still lying keeps it off the stone underneath. | | `ash_coverage` | 1 → 0. A film on everything that faces up and a drift packed into every joint and pit. | ## Read from the mesh `vertex_color.r` how freely ash lies here, `.g` whether this is built stonework or natural rock, `.b` how high up the crater it is. `craterGeo` writes all three. ## Why it holds at both ends of the film Two things, and both are load-bearing. Each band of detail is faded out as its features shrink below the size of a pixel (`ab_lod`, against the world-space footprint from the position derivatives). Left in, a sub-pixel octave is not detail, it is white noise that crawls as the camera moves — which is what a 250 m wide of a rock face looks like without this. And the specular lobe is widened by how much the shading normal varies across the pixel (`ab_specular_aa`). A pixel covering many bumps reflects a cone of directions, not one; shading it at the authored roughness turns wet basalt under a low moon into a field of sparkle. The shading normal itself comes from the height field's screen-space derivatives rather than a tangent-space normal map, because every mesh in this crater is generated at runtime and carries no tangents.