outfly/assets/shaders/jupiters_rings.wgsl

#import bevy_pbr::{
    mesh_view_bindings::globals,
    forward_io::VertexOutput,
}

@group(2) @binding(0) var<uniform> ring_radius: f32;
@group(2) @binding(1) var<uniform> jupiter_radius: f32;

const jupiter_radius_Mm: f32 = 71.492;
const brightness = 0.025;

fn smooth_edge(start: f32, end: f32, value: f32) -> f32 {
    var x: f32 = (value - start) / (end - start);
    return 4 * x * x * (1 - x * x);
}

//fn rand(co: vec2<f32>) -> f32 {
    //return fract(sin(dot(co, vec2(12.9898, 78.233))) * 43758.5453);
//}

//const PHI: f32 = 1.61803398874989484820459;
//fn gold_noise(xy: vec2<f32>, seed: f32) -> f32 {
    //return fract(tan(distance(xy*PHI, xy)*seed)*xy.x);
//}

fn ring_density(radius: f32) -> f32 {
    // NOTE: Keep this in sync with src/nature.rs::ring_density
    // Input: distance to center of jupiter in million meters
    // Output: relative brightness of the ring
    let halo_inner: f32 = 92.0;
    let halo_outer: f32 = 122.5;
    let main_inner: f32 = 122.5;
    let main_outer: f32 = 129.0;
    let amalthea_inner: f32 = 129.0;
    let amalthea_outer: f32 = 182.0;
    let thebe_inner: f32 = 129.0;
    let thebe_outer: f32 = 229.0;
    let metis_notch_center: f32 = 128.0;
    let metis_notch_width: f32 = 0.1;

    let halo_brightness: f32 = 0.75;
    let main_brightness: f32 = 1.0;
    let almathea_brightness: f32 = 0.5;
    let thebe_brightness: f32 = 0.5;

    var density: f32 = 0.0;

    if (radius >= halo_inner && radius <= halo_outer) {
        density = halo_brightness * smooth_edge(halo_inner, halo_outer, radius);
    } else if (radius >= main_inner && radius <= main_outer) {
        var metis_notch_effect: f32 = 1.0;
        if (radius > metis_notch_center - metis_notch_width * 0.5 && radius < metis_notch_center + metis_notch_width * 0.5) {
            metis_notch_effect = 0.8 * (1.0 - smooth_edge(metis_notch_center - metis_notch_width * 0.5, metis_notch_center + metis_notch_width * 0.5, radius));
        }
        density = main_brightness * metis_notch_effect * smooth_edge(main_inner, main_outer, radius);
    } else {
        if (radius >= amalthea_inner && radius <= amalthea_outer) {
            density = almathea_brightness * smooth_edge(amalthea_inner, amalthea_outer, radius);
        }
        if (radius >= thebe_inner && radius <= thebe_outer) {
            density += thebe_brightness * smooth_edge(thebe_inner, thebe_outer, radius);
        }
    }

    return density;
}

@fragment
fn fragment(in: VertexOutput) -> @location(0) vec4<f32> {
    let jupiter_percent = jupiter_radius / ring_radius;
    let color = vec3<f32>(0.3, 0.3, 0.3);
    var alpha = brightness;
    let r_uv = 2 * distance(in.uv, vec2<f32>(0.5));
    let r = r_uv * ring_radius / jupiter_radius * jupiter_radius_Mm;

    alpha *= ring_density(r);
    alpha -= 0.001;
    if alpha <= 0.0 {
        return vec4<f32>(color, 0.0);
    }

    if in.uv[0] < 0.5 {
        let dist = (0.5 - in.uv[0]) * 2.0; // 0.0=jupiter's center, 1.0=edge of the ring
        let side_dist = abs(in.uv[1] - 0.5);

        let cutoff = 0.5 * jupiter_percent * cos(dist);
        if side_dist < cutoff {
            return vec4<f32>(color, 0.0);
        }
        let fuzzy_boundary = 0.01;
        if side_dist < cutoff + fuzzy_boundary {
            return vec4<f32>(color, alpha * (side_dist - cutoff) / fuzzy_boundary);
        }
    }
    //if (sin(in.uv[0] * 1000.0) + cos(in.uv[1] * 10412.0) > 1.999) {
    //if (sin(in.uv[0] * 10000.0 + in.uv[1] * 5132.0) + cos(in.uv[0] * 12399.0 + in.uv[1] * 10412.0) > 1.999) {
    //if (sin(sin(in.uv[0] * 10000000.0) * 412.0 + cos(in.uv[1] * 11132000.0) * 12.0) + cos(sin(in.uv[0] * 12309900.0) * 93.0 + sin(in.uv[1] * 10410200.0) * 115.0) > 1.999) {
    //if (rand(in.uv) + rand(vec2(in.uv[1]*10.0, in.uv[0]*10.0)) > 1.997) {
        //alpha *= 200.0;
    //}
    return vec4<f32>(color, alpha);
}