# RTVolume

WebGPU software ray tracing of **procedural (AABB) geometry** with an
**any-hit** cut-out — the two features added for issue #13.

A 3×3×3 grid of unit boxes is registered as an AABB BLAS
(`Mesh::BuildProcedural`, the WebGPU analog of `VK_GEOMETRY_TYPE_AABBS_KHR`).
The hit group is a `RTShaderGroupType::ProceduralHitGroup` carrying:

- `intersection.wgsl` — analytic ray–sphere test that turns each box into a
  radius-1 sphere (runs in TRACE, once per box the ray enters);
- `anyhit.wgsl` — returns `RT_ANYHIT_IGNORE` for half the cells of a
  spherical checkerboard, so the ray passes through and the background /
  spheres behind show through (the visible proof any-hit runs);
- `closesthit.wgsl` — normal-based Lambert shading, tinted per instance.

The geometry is registered **non-opaque** and the instances clear their
force-opaque flag, which is what lets the any-hit shader run. Flip the
instance flag to `kRTGeometryInstanceForceOpaque` (or build the mesh with
`opaque = true`) to skip any-hit and see solid spheres.

WebGPU/DOM only:

```
crafter-build --target=wasm32-wasip1 -r
```