1// https://cwyman.org/papers/hpg21_rearchitectingReSTIR.pdf
2
3import bevy_pbr::render::rgb9e5::{vec3_to_rgb9e5_, rgb9e5_to_vec3_};
4import bevy_render::utils::{octahedral_encode, octahedral_decode};
5import package::scene::sampling::{generate_random_light_sample, ResolvedLightSample};
6import package::realtime::bindings::{light_tile_samples, light_tile_resolved_samples, view, constants, ResolvedLightSamplePacked};
7
8enable wgpu_ray_query;
9
10@compute @workgroup_size(1024, 1, 1)
11fn presample_light_tiles(@builtin(workgroup_id) workgroup_id: vec3<u32>, @builtin(local_invocation_index) sample_index: u32) {
12    let tile_id = workgroup_id.x;
13    var rng = (tile_id * 0x9E3779B9u) + sample_index + constants.frame_rng;
14
15    let sample = generate_random_light_sample(&rng);
16
17    let i = (tile_id * 1024u) + sample_index;
18    light_tile_samples[i] = sample.light_sample;
19    light_tile_resolved_samples[i] = pack_resolved_light_sample(sample.resolved_light_sample);
20}
21
22fn pack_resolved_light_sample(sample: ResolvedLightSample) -> ResolvedLightSamplePacked {
23    return ResolvedLightSamplePacked(
24        sample.world_position.x,
25        sample.world_position.y,
26        sample.world_position.z,
27        pack2x16unorm(octahedral_encode(sample.world_normal)),
28        vec3_to_rgb9e5_(log2(sample.radiance * view.exposure + 1.0)),
29        sample.inverse_pdf * select(1.0, -1.0, sample.world_position.w == 0.0),
30    );
31}
32
33fn unpack_resolved_light_sample(packed: ResolvedLightSamplePacked, exposure: f32) -> ResolvedLightSample {
34    return ResolvedLightSample(
35        vec4(packed.world_position_x, packed.world_position_y, packed.world_position_z, select(1.0, 0.0, packed.inverse_pdf < 0.0)),
36        octahedral_decode(unpack2x16unorm(packed.world_normal)),
37        (exp2(rgb9e5_to_vec3_(packed.radiance)) - 1.0) / exposure,
38        abs(packed.inverse_pdf),
39    );
40}