// Issue #37: GPU producer (WebGPU) for the procedural AABB build input.
// Writes the per-box bounding boxes straight into a device storage buffer
// that Mesh::BuildProcedural / RefitProcedural then consume by handle, with
// no host copy. Emits a single unit box [-r,r]^3 (the bounding volume the
// intersection shader turns into a sphere); `time` lets it breathe so the
// per-frame refit has something to track. A real particle system would write
// one box per particle from simulation state.
//
// PlainComputeShader layout (no rayQuery → user groups start at 1):
//   @group(0) @binding(0) uniform Params
//   @group(1) @binding(0) storage read_write boxes : array<f32>  (6 f32/box)

struct Params { count: u32, time: f32, _0: u32, _1: u32 };
@group(0) @binding(0) var<uniform> pc : Params;
@group(1) @binding(0) var<storage, read_write> boxes : array<f32>;

@compute @workgroup_size(64)
fn main(@builtin(global_invocation_id) gid: vec3<u32>) {
    let i = gid.x;
    if (i >= pc.count) { return; }
    let r = 1.0 + 0.15 * sin(pc.time);
    let b = i * 6u;
    boxes[b + 0u] = -r;
    boxes[b + 1u] = -r;
    boxes[b + 2u] = -r;
    boxes[b + 3u] =  r;
    boxes[b + 4u] =  r;
    boxes[b + 5u] =  r;
}