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;

//fn ring_density(r: f32) -> f32 {
//    // r is in terms of megameters.
////    if r < 92 {
////        return 0.0;
////    }
////    if r > 226 {
////        return 0.0;
////    }
//
//    let B0: f32 = 1.0;
//    let d0: f32 = 71492.0;
//    let lambda: f32 = 5000.0;
//    let alpha: f32 = 0.1;
//    let beta: f32 = 0.001;
//    let dist = r * 400;
//
//    let brightness: f32 = B0 * exp(-(dist - d0) / lambda) * (1.0 + alpha * sin(beta * (dist - d0)));
//    return brightness * 1;
//}

//fn ring_density(r: f32) -> f32 {
//    if r < jupiter_radius_Mm {
//        return 0.0;
//    }
//    if r > jupiter_radius_Mm * 3 {
//        return 0.0;
//    }
//    let radius = (r - jupiter_radius_Mm) / (jupiter_radius_Mm * 2) + 1;
//    // Constants representing the approximate normalized start, peak, and end radii of the rings
//    let halo_start: f32 = 1.1;
//    let halo_peak: f32 = 1.2;
//    let halo_end: f32 = 1.3;
//
//    let main_start: f32 = 1.4;
//    let main_peak: f32 = 1.5;
//    let main_end: f32 = 1.6;
//
//    let gossamer_start: f32 = 1.7;
//    let gossamer_peak: f32 = 1.8;
//    let gossamer_end: f32 = 1.9;
//
//    // Piecewise linear function for density approximation
//    if (radius >= halo_start && radius < halo_peak) {
//        return 1.0;
//        //return (radius - halo_start) / (halo_peak - halo_start);
//    } else if (radius >= halo_peak && radius <= halo_end) {
//        return 1.0 - (radius - halo_peak) / (halo_end - halo_peak);
//    } else if (radius >= main_start && radius < main_peak) {
//        return (radius - main_start) / (main_peak - main_start);
//    } else if (radius >= main_peak && radius <= main_end) {
//        return 1.0 - (radius - main_peak) / (main_end - main_peak);
//    } else if (radius >= gossamer_start && radius < gossamer_peak) {
//        return (radius - gossamer_start) / (gossamer_peak - gossamer_start);
//    } else if (radius >= gossamer_peak && radius <= gossamer_end) {
//        return 1.0 - (radius - gossamer_peak) / (gossamer_end - gossamer_peak);
//    }
//
//    return 0.0; // Outside of rings, density is 0
//}

//fn ring_density(radius: f32) -> f32 {
//    // Define key radii for Jupiter's rings and gaps
//    let inner_radius: f32 = 1.806e5; // Inner boundary of the Halo ring
//    let halo_main_gap: f32 = 1.22e5; // Gap between Halo and Main rings
//    let main_amalthea_gap: f32 = 1.8e5; // Gap between Main and Amalthea Gossamer ring
//    let amalthea_thebe_gap: f32 = 2.24e5; // Gap between Amalthea and Thebe Gossamer rings
//    let outer_radius: f32 = 2.2e5; // Outer boundary of Thebe Gossamer ring
//    let metis_notch_inner: f32 = 1.28e5; // Inner boundary of Metis notch
//    let metis_notch_outer: f32 = 1.29e5; // Outer boundary of Metis notch
//
//    // Density function
//    if radius > outer_radius {
//        return 0.0; // Beyond rings, density is zero
//    } else if radius > metis_notch_inner && radius < metis_notch_outer {
//        return 0.2; // Notch at the orbit of Metis
//    } else if radius > halo_main_gap && radius < main_amalthea_gap {
//        return 1.0; // Highest density in Main ring
//    } else if radius > amalthea_thebe_gap {
//        return 0.5; // Lower density in Thebe Gossamer ring
//    } else {
//        return 0.75; // Moderate density in other areas
//    }
//}

// Smooth step function for edge smoothing
fn smooth_edge(start: f32, end: f32, value: f32, smooth_factor: f32) -> f32 {
    var x = ((value - start) / (end - start));
    if x < 0 {
        return 0.0;
    }
    if x > 1 {
        return 1.0;
    }
    return pow(x, smooth_factor) * (3.0 - 2.0 * x);
}
fn ring_density(radius: f32) -> f32 {
    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 = 0.6;

    let halo_brightness: f32 = 0.4;
    let main_brightness: f32 = 1.0;
    let almathea_brightness: f32 = 0.3;
    let thebe_brightness: f32 = 0.2;

    let smooth_factor: f32 = 2.0; // Smooth edges

    if radius < halo_inner || radius > thebe_outer {
        return 0.0;
    } else if radius >= halo_inner && radius <= halo_outer {
        return halo_brightness * smooth_edge(halo_inner, halo_outer, radius, smooth_factor);
    } else if radius >= main_inner && radius <= main_outer {
        var metis_notch_effect = 1.0;
        if radius > metis_notch_center - metis_notch_width * 0.5 && radius < metis_notch_center + metis_notch_width * 0.5 {
            metis_notch_effect = 0.5 * (1.0 - smooth_edge(metis_notch_center - metis_notch_width * 0.5, metis_notch_center + metis_notch_width * 0.5, radius, smooth_factor));
        }
        return main_brightness * metis_notch_effect * smooth_edge(main_inner, main_outer, radius, smooth_factor);
    } else if radius >= amalthea_inner && radius <= amalthea_outer {
        return almathea_brightness * smooth_edge(amalthea_inner, amalthea_outer, radius, smooth_factor);
    } else if radius >= thebe_inner && radius <= thebe_outer {
        return thebe_brightness * smooth_edge(thebe_inner, thebe_outer, radius, smooth_factor);
    }
    return 0.0;
}

fn smooth_edge2(start: f32, end: f32, value: f32) -> f32 {
    var x: f32 = (value - start) / (end - start);
    return 4 * x * x * (1 - x * x);
}

fn ring_density2(radius: f32) -> f32 {
    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 = 0.6;

    let halo_brightness: f32 = 0.3;
    let main_brightness: f32 = 1.0;
    let almathea_brightness: f32 = 0.2;
    let thebe_brightness: f32 = 0.2;

    let inner_smooth_factor: f32 = 2.0; // Smooth inner edges
    let outer_smooth_factor: f32 = 1.5; // Rougher outer edges

    var density: f32 = 0.0;

    if (radius >= halo_inner && radius <= halo_outer) {
        density = halo_brightness * smooth_edge2(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 = 0.5 * (1.0 - smooth_edge2(metis_notch_center - metis_notch_width * 0.5, metis_notch_center + metis_notch_width * 0.5, radius));
        }
        density = main_brightness * metis_notch_effect * smooth_edge2(main_inner, main_outer, radius);
    } else {
        if (radius >= amalthea_inner && radius <= amalthea_outer) {
            density = almathea_brightness * smooth_edge2(amalthea_inner, amalthea_outer, radius);
        }
        if (radius >= thebe_inner && radius <= thebe_outer) {
            density += thebe_brightness * smooth_edge2(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 = 0.04;
    let r_uv = 2 * distance(in.uv, vec2<f32>(0.5));
    let r = r_uv * ring_radius / jupiter_radius * jupiter_radius_Mm;

    alpha *= ring_density2(r);
    if alpha <= 0.0 {
        return vec4<f32>(color, alpha);
    }

    //alpha *= (sin(11*r / 0.71 * 3.1415) + 1) / 2;
    //alpha *= (cos(r / 0.72 * 3.1415) + 1) / 2;

    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);
        }
    }
    return vec4<f32>(color, alpha);
}