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<rgba32float, read>;
8
9@group(0) @binding(1) var output: texture_storage_2d<rgba32float, write>;
10
11@group(0) @binding(2) var<uniform> config: GameOfLifeUniforms;
12
13struct GameOfLifeUniforms {
14    alive_color: vec4<f32>,
15}
16
17fn hash(value: u32) -> u32 {
18    var state = value;
19    state = state ^ 2747636419u;
20    state = state * 2654435769u;
21    state = state ^ (state >> 16u);
22    state = state * 2654435769u;
23    state = state ^ (state >> 16u);
24    state = state * 2654435769u;
25    return state;
26}
27
28fn randomFloat(value: u32) -> f32 {
29    return f32(hash(value)) / 4294967295.0;
30}
31
32@compute @workgroup_size(8, 8, 1)
33fn init(@builtin(global_invocation_id) invocation_id: vec3<u32>, @builtin(num_workgroups) num_workgroups: vec3<u32>) {
34    let location = vec2<i32>(i32(invocation_id.x), i32(invocation_id.y));
35
36    let randomNumber = randomFloat((invocation_id.y << 16u) | invocation_id.x);
37    let alive = randomNumber > 0.9;
38    // Use alpha channel to keep track of cell's state
39    let color = vec4(config.alive_color.rgb, f32(alive));
40
41    textureStore(output, location, color);
42}
43
44fn is_alive(location: vec2<i32>, offset_x: i32, offset_y: i32) -> i32 {
45    let value: vec4<f32> = textureLoad(input, location + vec2<i32>(offset_x, offset_y));
46    return i32(value.a);
47}
48
49fn count_alive(location: vec2<i32>) -> i32 {
50    return is_alive(location, -1, -1) +
51           is_alive(location, -1,  0) +
52           is_alive(location, -1,  1) +
53           is_alive(location,  0, -1) +
54           is_alive(location,  0,  1) +
55           is_alive(location,  1, -1) +
56           is_alive(location,  1,  0) +
57           is_alive(location,  1,  1);
58}
59
60@compute @workgroup_size(8, 8, 1)
61fn update(@builtin(global_invocation_id) invocation_id: vec3<u32>) {
62    let location = vec2<i32>(i32(invocation_id.x), i32(invocation_id.y));
63
64    let n_alive = count_alive(location);
65
66    var alive: bool;
67    if (n_alive == 3) {
68        alive = true;
69    } else if (n_alive == 2) {
70        let currently_alive = is_alive(location, 0, 0);
71        alive = bool(currently_alive);
72    } else {
73        alive = false;
74    }
75    let color = vec4(config.alive_color.rgb, f32(alive));
76
77    textureStore(output, location, color);
78}