# RayQueryPick

Regression test for the WebGPU software **ray-query** shim
(`additional/dom-webgpu.js`, `_rqTraverseTlas`).

Builds an 8³ = 512-instance TLAS and shoots one fully-determined ray
through a `rayQuery=true` `PlainComputeShader`. The committed hit is read
back to the host and checked against the analytically-known answer
(instance `customIndex = 484`, `t = 40.75`). On success the console prints:

```
[RayQueryPick] result: hit=1 customIndex=484 prim=6 t=40.75
[RayQueryPick] PASS — rayQuery TLAS traversal hit the expected instance
```

## Why 512 instances

The TLAS sweep tree is padded to `next_pow2(instanceCount)` leaves. The
rayQuery shim used to detect BVH leaves with a hardcoded `16384 - 1` leaf
start, so for any scene with fewer than 8193 instances **no node index
ever reached a leaf** and every pick missed (issue #25). 512 sits squarely
in that broken regime, so this example fails fast if the shim regresses to
a static leaf start. The shim now derives the leaf start from a per-build
`RqTlasMeta.nPadded` uniform, matching the megakernel `_rtwTraverseTlas`.

The scene also renders through the wavefront RT pipeline (same as
RTStress) so the run produces a visible frame, but the pass/fail signal is
the console line above.

```bash
cd examples/RayQueryPick
crafter-build -r --target=wasm32-wasip1
```

WebGPU/DOM only — the native path uses hardware ray queries.