1// Reimplementation of the approach in Crest Shaders/Resources/ShapeCombine.compute.
2
3const LOD_COUNT: u32 = 5u;
4const CASCADE_COUNT: u32 = LOD_COUNT + 1u;
5const WAVE_COUNT: u32 = 40u;
6
7struct CascadeParams {
8    center: vec2<f32>,
9    scale: f32,
10    texture_res: f32,
11    inv_texture_res: f32,
12    texel_width: f32,
13    weight: f32,
14    max_wavelength: f32,
15}
16struct CascadeLayout {
17    cascades: array<CascadeParams, CASCADE_COUNT>,
18    center: vec4<f32>,
19    // XY bed-map first-texel world origin, ZW inverse world extent.
20    bed_transform: vec4<f32>,
21    // X height minimum, Y height span (negative = no bed map), Z sea level.
22    bed_range: vec4<f32>,
23}
24struct GerstnerWave {
25    direction: vec2<f32>,
26    amplitude: f32,
27    wave_number: f32,
28    angular_frequency: f32,
29    phase: f32,
30    chop_amplitude: f32,
31}
32struct AnimWavesUniform {
33    cascade_layout: CascadeLayout,
34    waves: array<GerstnerWave, WAVE_COUNT>,
35    ranges: array<vec4<u32>, LOD_COUNT>,
36    time: vec4<f32>,
37    // xy: world-space current in m/s; kept identical to the other
38    // AnimWavesUniform declarations so one upload serves every consumer.
39    flow: vec4<f32>,
40}
41
42@group(0) @binding(0) var raw_waves: texture_2d_array<f32>;
43@group(0) @binding(1) var previous: texture_2d_array<f32>;
44@group(0) @binding(2) var linear_sampler: sampler;
45@group(0) @binding(3) var output: texture_storage_2d_array<rgba16float, write>;
46@group(0) @binding(4) var<uniform> params: AnimWavesUniform;
47
48fn combine_lod(id: vec3<u32>, slice: u32) {
49    let cascade = params.cascade_layout.cascades[slice];
50    if id.x >= u32(cascade.texture_res) || id.y >= u32(cascade.texture_res) {
51        return;
52    }
53    var displacement = textureLoad(raw_waves, vec2<i32>(id.xy), i32(slice), 0).xyz;
54    if slice + 1u < LOD_COUNT {
55        let uv = (vec2<f32>(id.xy) + vec2(0.5)) * cascade.inv_texture_res;
56        let coverage = cascade.texel_width * cascade.texture_res;
57        let world_xz = coverage * (uv - vec2(0.5)) + cascade.center;
58        let next = params.cascade_layout.cascades[slice + 1u];
59        let next_coverage = next.texel_width * next.texture_res;
60        let next_uv = (world_xz - next.center) / next_coverage + vec2(0.5);
61        displacement += textureSampleLevel(
62            previous,
63            linear_sampler,
64            next_uv,
65            i32(slice + 1u),
66            0.0,
67        ).xyz;
68    }
69    textureStore(output, vec2<i32>(id.xy), i32(slice), vec4(displacement, 0.0));
70}
71
72#ifdef COMBINE_1
73@compute @workgroup_size(8, 8, 1)
74fn main(@builtin(global_invocation_id) id: vec3<u32>) { combine_lod(id, 1u); }
75#endif
76#ifdef COMBINE_2
77@compute @workgroup_size(8, 8, 1)
78fn main(@builtin(global_invocation_id) id: vec3<u32>) { combine_lod(id, 2u); }
79#endif
80#ifdef COMBINE_3
81@compute @workgroup_size(8, 8, 1)
82fn main(@builtin(global_invocation_id) id: vec3<u32>) { combine_lod(id, 3u); }
83#endif
84#ifdef COMBINE_4
85@compute @workgroup_size(8, 8, 1)
86fn main(@builtin(global_invocation_id) id: vec3<u32>) { combine_lod(id, 4u); }
87#endif
88#ifdef COMBINE_0
89@compute @workgroup_size(8, 8, 1)
90fn main(@builtin(global_invocation_id) id: vec3<u32>) { combine_lod(id, 0u); }
91#endif