craters-compute.wgsl

@group(0) @binding(0) var<storage, read_write> moon_height_data: MoonHeightData;

fn smooth_min(a: f32, b: f32, t: f32) -> f32 {
    let h: f32 = clamp(0.5 + 0.5 * (b - a) / t, 0.0, 1.0);

    return mix(b, a, h) - t * h * (1.0 - h);
}

fn smooth_max(a: f32, b: f32, t: f32) -> f32 {
    return smooth_min(a, b, -t);
}

@compute @workgroup_size(128, 1, 1)
fn compute_moon_height(
    @builtin(global_invocation_id) invocation_id: vec3<u32>,
    @builtin(num_workgroups) num_workgroups: vec3<u32>
) {
    let data = moon_height_data;
    let id = invocation_id.x;

    if id >= moon_height_data.num_vertices {
        return;
    }

    let vertex_pos = moon_height_data.vertices[invocation_id.x];
    var crater_height = 0.0;

    for (var i: i32 = 0; i < data.num_craters; i++) {
        // Can't access arrays with a non-constant! How to fix?
        let x: f32 = length(vertex_pos - data.craters[i].center) / data.craters[i].radius;

        let cavity: f32 = x * x - 1.0;
        let rim_x: f32 = min(x - 1.0 - data.rim_width, 0.0);
        let rim: f32 = data.rim_steepness * rim_x * rim_x;

        var crater_shape: f32 = smooth_max(cavity, data.floor_height, data.smoothness);
        crater_shape = smooth_min(crater_shape, rim, data.smoothness);
        crater_height += crater_shape * data.craters[i].radius;
    }

    data.heights[0] = 0.0;
    data.heights[id] = 1.0 + crater_height;
}