1// The shader reads the previous frame's state from the `input` texture, and writes the new state of
2// each pixel to the `output` texture. The textures are flipped each step to progress the
3// simulation.
4// Two textures are needed for the game of life as each pixel of step N depends on the state of its
5// neighbors at step N-1.
6
7@group(0) @binding(0) var input: texture_storage_2d<r32float, read>;
8
9@group(0) @binding(1) var output: texture_storage_2d<r32float, write>;
10
11fn hash(value: u32) -> u32 {
12    var state = value;
13    state = state ^ 2747636419u;
14    state = state * 2654435769u;
15    state = state ^ state >> 16u;
16    state = state * 2654435769u;
17    state = state ^ state >> 16u;
18    state = state * 2654435769u;
19    return state;
20}
21
22fn randomFloat(value: u32) -> f32 {
23    return f32(hash(value)) / 4294967295.0;
24}
25
26@compute @workgroup_size(8, 8, 1)
27fn init(@builtin(global_invocation_id) invocation_id: vec3<u32>, @builtin(num_workgroups) num_workgroups: vec3<u32>) {
28    let location = vec2<i32>(i32(invocation_id.x), i32(invocation_id.y));
29
30    let randomNumber = randomFloat(invocation_id.y << 16u  | invocation_id.x);
31    let alive = randomNumber > 0.9;
32    let color = vec4<f32>(f32(alive));
33
34    textureStore(output, location, color);
35}
36
37fn is_alive(location: vec2<i32>, offset_x: i32, offset_y: i32) -> i32 {
38    let value: vec4<f32> = textureLoad(input, location + vec2<i32>(offset_x, offset_y));
39    return i32(value.x);
40}
41
42fn count_alive(location: vec2<i32>) -> i32 {
43    return is_alive(location, -1, -1) +
44           is_alive(location, -1,  0) +
45           is_alive(location, -1,  1) +
46           is_alive(location,  0, -1) +
47           is_alive(location,  0,  1) +
48           is_alive(location,  1, -1) +
49           is_alive(location,  1,  0) +
50           is_alive(location,  1,  1);
51}
52
53@compute @workgroup_size(8, 8, 1)
54fn update(@builtin(global_invocation_id) invocation_id: vec3<u32>) {
55    let location = vec2<i32>(i32(invocation_id.x), i32(invocation_id.y));
56
57    let n_alive = count_alive(location);
58
59    var alive: bool;
60    if (n_alive == 3) {
61        alive = true;
62    } else if (n_alive == 2) {
63        let currently_alive = is_alive(location, 0, 0);
64        alive = bool(currently_alive);
65    } else {
66        alive = false;
67    }
68    let color = vec4<f32>(f32(alive));
69
70    textureStore(output, location, color);
71}