Function build_brdf_lut

native/shared/src/renderer/brdf_lut.rs:128–154

Build a `size × size` BRDF LUT as packed Rg16Float texels. Each row is constant `roughness` (v axis), each column constant `NdotV` (u axis). Output is row-major suitable for write_texture. Splits across `available_parallelism()` threads since cells are independent — keeps startup latency manageable even at 1024 spp.

(size: usize)

/// across `available_parallelism()` threads since cells are
/// independent — keeps startup latency manageable even at 1024 spp.
pub fn build_brdf_lut(size: usize) -> Vec<u16> {
    #[cfg(not(target_arch = "wasm32"))]
    {
        let nthreads = std::thread::available_parallelism().map(|n| n.get()).unwrap_or(4);
        let rows_per_thread = (size + nthreads - 1) / nthreads;
        let mut all_rows: Vec<Option<Vec<Vec<u16>>>> = (0..nthreads).map(|_| None).collect();
        std::thread::scope(|s| {
            let mut handles = Vec::with_capacity(nthreads);
            for t in 0..nthreads {
                let y_start = t * rows_per_thread;
                let y_end = ((t + 1) * rows_per_thread).min(size);
                let h = s.spawn(move || {
                    (y_start..y_end).map(|y| build_brdf_lut_row(y, size)).collect::<Vec<_>>()
                });
                handles.push(h);
            }
            for (t, h) in handles.into_iter().enumerate() {
                all_rows[t] = Some(h.join().unwrap());
            }
        });
        all_rows.into_iter().flatten().flatten().flatten().collect()
    }
    #[cfg(target_arch = "wasm32")]
    {
        (0..size).flat_map(|y| build_brdf_lut_row(y, size)).collect()
    }
}