veloren/assets/voxygen/shaders/include/sky.glsl

#include <random.glsl>
#include <srgb.glsl>
#include <cloud.glsl>
#include <srgb.glsl>
#include <shadows.glsl>

// Information about an approximately directional light, like the sun or moon.
struct DirectionalLight {
    // vec3 dir;
    float shadow;
    // vec3 color;
    // float brightness;
};

const float PI = 3.141592;

const vec3 SKY_DAY_TOP = vec3(0.1, 0.5, 0.9);
const vec3 SKY_DAY_MID = vec3(0.02, 0.28, 0.8);
const vec3 SKY_DAY_BOT = vec3(0.1, 0.2, 0.3);
const vec3 DAY_LIGHT   = vec3(1.5, 1.4, 1.0);//vec3(1.5, 1.4, 1.0);
const vec3 SUN_HALO_DAY = vec3(0.35, 0.35, 0.0);

const vec3 SKY_DUSK_TOP = vec3(0.06, 0.1, 0.20);
const vec3 SKY_DUSK_MID = vec3(0.35, 0.1, 0.15);
const vec3 SKY_DUSK_BOT = vec3(0.0, 0.1, 0.23);
const vec3 DUSK_LIGHT   = vec3(8.0, 1.5, 0.15);
const vec3 SUN_HALO_DUSK = vec3(1.2, 0.15, 0.0);

const vec3 SKY_NIGHT_TOP = vec3(0.001, 0.001, 0.0025);
const vec3 SKY_NIGHT_MID = vec3(0.001, 0.005, 0.02);
const vec3 SKY_NIGHT_BOT = vec3(0.002, 0.004, 0.004);
const vec3 NIGHT_LIGHT   = vec3(0.002, 0.02, 0.02);
// const vec3 NIGHT_LIGHT   = vec3(0.0, 0.0, 0.0);

// Linear RGB, scattering coefficients for atmosphere at roughly R, G, B wavelengths.
//
// See https://en.wikipedia.org/wiki/Diffuse_sky_radiation
const vec3 MU_SCATTER = vec3(0.05, 0.10, 0.23) * 2.0;

const float SUN_COLOR_FACTOR = 6.0;//6.0;// * 1.5;//1.8;

const float UNDERWATER_MIST_DIST = 100.0;

const float PERSISTENT_AMBIANCE = 1.0 / 512;// 1.0 / 512; // 0.00125 // 0.1;// 0.025; // 0.1;

//vec3 get_sun_dir(float time_of_day) {
//    const float TIME_FACTOR = (PI * 2.0) / (3600.0 * 24.0);
//
//    float sun_angle_rad = time_of_day * TIME_FACTOR;
//    // return vec3(sin(sun_angle_rad), 0.0, cos(sun_angle_rad));
//    return vec3(sin(sun_angle_rad), 0.0, cos(sun_angle_rad));
//}
//
//vec3 get_moon_dir(float time_of_day) {
//    const float TIME_FACTOR = (PI * 2.0) / (3600.0 * 24.0);
//
//    float moon_angle_rad = time_of_day * TIME_FACTOR;
//    // -cos((60+60*4)/360*2*pi)-0.5 = 0
//    // -cos((60+60*5)/360*2*pi)-0.5 = -0.5
//    // -cos((60+60*6)/360*2*pi)-0.5 = 0
//    //
//    // i.e. moon out from (60*5)/360*24 = 20:00 to (60*7/360*24) = 28:00 = 04:00.
//    //
//    // Then sun out from 04:00 to 20:00.
//    return normalize(-vec3(sin(moon_angle_rad), 0.0, cos(moon_angle_rad) - 0.5));
//}

float get_sun_brightness(/*vec3 sun_dir*/) {
    return max(-sun_dir.z + 0.6, 0.0) * 0.9;
}

float get_moon_brightness(/*vec3 moon_dir*/) {
    return max(-moon_dir.z + 0.6, 0.0) * 0.4;
}

vec3 get_sun_color(/*vec3 sun_dir*/) {
    return mix(
        mix(
            DUSK_LIGHT,
            NIGHT_LIGHT,
            max(sun_dir.z, 0)
        ),
        DAY_LIGHT,
        max(-sun_dir.z, 0)
    );
}

vec3 get_moon_color(/*vec3 moon_dir*/) {
    return vec3(0.05, 0.05, 0.6);
}

DirectionalLight get_sun_info(vec4 _dir, float shade_frac/*, vec4 light_pos[2]*/, /*vec4 sun_pos*/vec3 f_pos) {
    float shadow = shade_frac;
#ifdef HAS_SHADOW_MAPS
#if (SHADOW_MODE == SHADOW_MODE_MAP)
    if (sun_dir.z < /*0.6*/0.0) {
        /* ShadowLocals sun_shadow = shadowMats[0];
        vec4 sun_pos = sun_shadow.texture_mat * vec4(f_pos, 1.0); */
// #if (SHADOW_MODE == SHADOW_MODE_MAP)
//     // for (uint i = 0u; i < light_shadow_count.z; ++i) {
//     //     light_pos[i] = /*vec3(*/shadowMats[i].texture_mat * vec4(f_pos, 1.0)/*)*/;
//     // }
// #elif (SHADOW_MODE == SHADOW_MODE_CHEAP || SHADOW_MODE == SHADOW_MODE_NONE)
//     vec4 sun_pos = vec4(0.0);
// #endif
        shadow = min(shadow, ShadowCalculationDirected(/*sun_pos, *//*0u*/f_pos));
    }
#endif
#endif
    return DirectionalLight(/*dir, */shadow/*, get_sun_color(dir), get_sun_brightness(dir)*/);
}

DirectionalLight get_moon_info(vec4 _dir, float shade_frac/*, vec4 light_pos[2]*/) {
    float shadow = shade_frac;
// #ifdef HAS_SHADOW_MAPS
//     shadow = min(shade_frac, ShadowCalculationDirected(light_pos, 1u));
// #endif
    return DirectionalLight(/*dir, */shadow/*, get_moon_color(dir), get_moon_brightness(dir)*/);
}

// // Calculates extra emission and reflectance (due to sunlight / moonlight).
// //
// // reflectence = k_a * i_a + i_a,persistent
// // emittence = Σ { m ∈ lights } i_m * shadow_m * get_light_reflected(light_m)
// //
// // Note that any shadowing to be done that would block the sun and moon, aside from heightmap shadowing (that will be
// // implemented sooon), should be implicitly provided via k_a, k_d, and k_s.  For instance, shadowing via ambient occlusion.
// //
// // Also note that the emitted light calculation is kind of lame... we probabbly need something a bit nicer if we ever want to do
// // anything interesting here.
// // void get_sun_diffuse(vec3 norm, float time_of_day, out vec3 light, out vec3 diffuse_light, out vec3 ambient_light, float diffusion
// void get_sun_diffuse(vec3 norm, float time_of_day, vec3 dir, vec3 k_a, vec3 k_d, vec3 k_s, float alpha, out vec3 emitted_light, out vec3 reflected_light) {
//     const float SUN_AMBIANCE = 0.1 / 2.0;// 0.1 / 3.0;
//
//     vec3 sun_dir = get_sun_dir(time_of_day);
//     vec3 moon_dir = get_moon_dir(time_of_day);
//
//     float sun_light = get_sun_brightness(sun_dir);
//     float moon_light = get_moon_brightness(moon_dir);
//
//     vec3 sun_color = get_sun_color(sun_dir);
//     vec3 moon_color = get_moon_color(moon_dir);
//
//     vec3 sun_chroma = sun_color * sun_light;
//     vec3 moon_chroma = moon_color * moon_light;
//
//     /* float NLsun = max(dot(-norm, sun_dir), 0);
//     float NLmoon = max(dot(-norm, moon_dir), 0);
//     vec3 E = -dir; */
//
//     // Globbal illumination "estimate" used to light the faces of voxels which are parallel to the sun or moon (which is a very common occurrence).
//     // Will be attenuated by k_d, which is assumed to carry any additional ambient occlusion information (e.g. about shadowing).
//     float ambient_sides = clamp(mix(0.5, 0.0, abs(dot(-norm, sun_dir)) * mix(0.0, 1.0, abs(sun_dir.z) * 10000.0) * 10000.0), 0.0, 0.5);
//     // float ambient_sides = 0.5 - 0.5 * abs(dot(-norm, sun_dir));
//
//     emitted_light = k_a * (ambient_sides + vec3(SUN_AMBIANCE * sun_light + moon_light)) + PERSISTENT_AMBIANCE;
//     // TODO: Add shadows.
//     reflected_light =
//         sun_chroma * light_reflection_factor(norm, dir, sun_dir, k_d, k_s, alpha) +
//         moon_chroma * 1.0 * /*4.0 * */light_reflection_factor(norm, dir, moon_dir, k_d, k_s, alpha);
//
//     /* light = sun_chroma + moon_chroma + PERSISTENT_AMBIANCE;
//     diffuse_light =
//         sun_chroma * mix(1.0, max(dot(-norm, sun_dir) * 0.5 + 0.5, 0.0), diffusion) +
//         moon_chroma * mix(1.0, pow(dot(-norm, moon_dir) * 2.0, 2.0), diffusion) +
//         PERSISTENT_AMBIANCE;
//     ambient_light = vec3(SUN_AMBIANCE * sun_light + moon_light); */
// }

// Returns computed maximum intensity.
//
// wpos is the position of this fragment.
// mu is the attenuation coefficient for any substance on a horizontal plane.
// cam_attenuation is the total light attenuation due to the substance for beams between the point and the camera.
// surface_alt is the altitude of the attenuating surface.
float get_sun_diffuse2(DirectionalLight sun_info, DirectionalLight moon_info, vec3 norm, vec3 dir, vec3 wpos, vec3 mu, vec3 cam_attenuation, float surface_alt, vec3 k_a, vec3 k_d, vec3 k_s, float alpha, vec3 voxel_norm, float voxel_lighting, out vec3 emitted_light, out vec3 reflected_light) {
    const float MIN_SHADOW = 0.15;
    const vec3 SUN_AMBIANCE = MU_SCATTER;//0.23;/* / 1.8*/;// 0.1 / 3.0;
    const vec3 MOON_AMBIANCE = MU_SCATTER;//0.23;//0.1;

    /* vec3 sun_dir = sun_info.dir;
    vec3 moon_dir = moon_info.dir; */
    vec3 sun_dir = sun_dir.xyz;
    vec3 moon_dir = moon_dir.xyz;

    float sun_light = get_sun_brightness(/*sun_dir*/);//sun_info.brightness;;
    float moon_light = get_moon_brightness(/*moon_dir*/);//moon_info.brightness;

    vec3 sun_color = get_sun_color(/*sun_dir*/) * SUN_COLOR_FACTOR;//sun_info.color * SUN_COLOR_FACTOR;
    vec3 moon_color = get_moon_color(/*moon_dir*/);//moon_info.color;

    // If the sun is facing the wrong way, we currently just want zero light, hence default point is wpos.
    vec3 sun_attenuation = compute_attenuation(wpos, -sun_dir, mu, surface_alt, wpos);
    vec3 moon_attenuation = compute_attenuation(wpos, -moon_dir, mu, surface_alt, wpos);

    vec3 sun_chroma = sun_color * sun_light * cam_attenuation * sun_attenuation;
    vec3 moon_chroma = moon_color * moon_light * cam_attenuation * moon_attenuation;

// #ifdef HAS_SHADOW_MAPS
//     float sun_shadow = ShadowCalculationDirected(light_pos, 0u);
//     float moon_shadow = ShadowCalculationDirected(light_pos, 1u);
// #else
//     float sun_shadow = 1.0;
//     float moon_shadow = 1.0;
// #endif
    float sun_shadow = sun_info.shadow;
    float moon_shadow = moon_info.shadow;

    // https://en.m.wikipedia.org/wiki/Diffuse_sky_radiation
    //
    // HdRd radiation should come in at angle normal to us.
    // const float H_d = 0.23;
    //
    // Let β be the angle from horizontal
    // (for objects exposed to the sky, where positive when sloping towards south and negative when sloping towards north):
    //
    //     sin β = (north ⋅ norm) / |north||norm|
    //           = dot(vec3(0, 1, 0), norm)
    //
    //     cos β = sqrt(1.0 - dot(vec3(0, 1, 0), norm))
    //
    // Let h be the hour angle (180/0.0 at midnight, 90/1.0 at dawn, 0/0.0 at noon, -90/-1.0 at dusk, -180 at midnight/0.0):
    //     cos h = (midnight ⋅ -light_dir) / |midnight||-light_dir|
    //           = (noon ⋅ light_dir) / |noon||light_dir|
    //           = dot(vec3(0, 0, 1), light_dir)
    //
    // Let φ be the latitude at this point. 0 at equator, -90 at south pole / 90 at north pole.
    //
    // Let δ be the solar declination (angular distance of the sun's rays north [or south[]
    // of the equator), i.e. the angle made by the line joining the centers of the sun and Earth with its projection on the
    // equatorial plane.  Caused by axial tilt, and 0 at equinoxes.  Normally varies between -23.45 and 23.45 degrees.
    //
    // Let α (the solar altitude / altitud3 angle) be the vertical angle between the projection of the sun's rays on the
    // horizontal plane and the direction of the sun's rays (passing through a point).
    //
    // Let Θ_z be the vertical angle between sun's rays and a line perpendicular to the horizontal plane through a point,
    // i.e.
    //
    // Θ_z = (π/2) - α
    //
    // i.e. cos Θ_z = sin α and
    //      cos α = sin Θ_z
    //
    // Let γ_s be the horizontal angle measured from north to the horizontal projection of the sun's rays (positive when
    // measured westwise).
    //
    // cos Θ_z = cos φ cos h cos δ + sin φ sin δ
    // cos γ_s = sec α (cos φ sin δ - cos δ sin φ cos h)
    //         = (1  / √(1 - cos² Θ_z)) (cos φ sin δ - cos δ sin φ cos h)
    // sin γ_s = sec α cos δ sin h
    //         = (1 / cos α) cos δ sin h
    //         = (1 / sin Θ_z) cos δ sin h
    //         = (1  / √(1 - cos² Θ_z)) cos δ sin h
    //
    // R_b = (sin(δ)sin(φ - β) + cos(δ)cos(h)cos(φ - β))/(sin(δ)sin(φ) + cos(δ)cos(h)cos(φ))
    //
    // Assuming we are on the equator (i.e. φ = 0), and there is no axial tilt or we are at an equinox (i.e. δ = 0):
    //
    // cos Θ_z = 1 * cos h * 1 + 0 * 0 = cos h
    // cos γ_s = (1  / √(1 - cos² h)) (1 * 0 - 1 * 0 * cos h)
    //         = (1  / √(1 - cos² h)) * 0
    //         = 0
    // sin γ_s = (1  / √(1 - cos² h)) * sin h
    //         = sin h / sin h
    //         = 1
    //
    // R_b = (0 * sin(0 - β) + 1 * cos(h) * cos(0 - β))/(0 * 0 + 1 * cos(h) * 1)
    //     = (cos(h)cos(-β)) / cos(H)
    //     = cos(-β), the angle from horizontal.
    //
    // NOTE: cos(-β) = cos(β).
    // float cos_sun = dot(norm, /*-sun_dir*/vec3(0, 0, 1));
    // float cos_moon = dot(norm, -moon_dir);
    //
    // Let ζ = diffuse reflectance of surrounding ground for solar radiation, then we have
    //
    // R_d = (1 + cos β) / 2
    // R_r = ζ (1 - cos β) / 2
    //
    // H_t = H_b R_b + H_d R_d + (H_b + H_d) R_r
    float sin_beta = dot(vec3(0, 1, 0), norm);
    float R_b = sqrt(1.0 - sin_beta * sin_beta);
    // Rough estimate of diffuse reflectance of rest of ground.
    // NOTE: zeta should be close to 0.7 with snow cover, 0.2 normally?  Maybe?
    vec3 zeta = max(vec3(0.2), k_d * (1.0 - k_s));//vec3(0.2);// k_d * (1.0 - k_s);
    float R_d = (1 + R_b) * 0.5;
    vec3 R_r = zeta * (1.0 - R_b) * 0.5;
    //
    // We can break this down into:
    //      H_t_b = H_b * (R_b + R_r) = light_intensity * (R_b + R_r)
    //      H_t_r = H_d * (R_d + R_r) = light_intensity * (R_d + R_r)
    vec3 R_t_b = R_b + R_r;
    vec3 R_t_r = R_d + R_r;

    // vec3 half_vec = normalize(-norm + dir);
    vec3 light_frac = R_t_b * (sun_chroma * SUN_AMBIANCE + moon_chroma * MOON_AMBIANCE) * light_reflection_factor(norm, /*norm*//*dir*/dir, /*-norm*/-/*dir*/norm, /*k_d*/k_d/* * (1.0 - k_s)*/, /*k_s*/vec3(0.0), alpha, voxel_norm, voxel_lighting);
    // vec3 light_frac = /*vec3(1.0)*//*H_d * */
    //     SUN_AMBIANCE * /*sun_light*/sun_chroma * light_reflection_factor(norm, dir, /*vec3(0, 0, -1.0)*/-norm, vec3((1.0 + cos_sun) * 0.5), vec3(k_s * (1.0 - cos_sun) * 0.5), alpha) +
    //     MOON_AMBIANCE * /*sun_light*/moon_chroma * light_reflection_factor(norm, dir, /*vec3(0, 0, -1.0)*/-norm, vec3((1.0 + cos_moon) * 0.5), vec3(k_s * (1.0 - cos_moon) * 0.5), alpha);
    /* float NLsun = max(dot(-norm, sun_dir), 0);
    float NLmoon = max(dot(-norm, moon_dir), 0);
    vec3 E = -dir; */

    // Globbal illumination "estimate" used to light the faces of voxels which are parallel to the sun or moon (which is a very common occurrence).
    // Will be attenuated by k_d, which is assumed to carry any additional ambient occlusion information (e.g. about shadowing).
    // float ambient_sides = 0.0;
    // float ambient_sides = 0.5 - 0.5 * min(abs(dot(-norm, sun_dir)), abs(dot(-norm, moon_dir)));
    // float ambient_sides = clamp(mix(0.5, 0.0, abs(dot(-norm, sun_dir)) * mix(0.0, 1.0, abs(sun_dir.z) * 10000.0) * 10000.0), 0.0, 0.5);
    // float ambient_sides = clamp(mix(0.5, 0.0, abs(dot(-norm, sun_dir)) * mix(0.0, 1.0, abs(sun_dir.z) * 10000.0) * 10000.0), 0.0, 0.5);

    emitted_light = light_frac + k_a * PERSISTENT_AMBIANCE;
    // emitted_light = k_a * light_frac * (/*ambient_sides + */SUN_AMBIANCE * /*sun_light*/sun_chroma + /*vec3(moon_light)*/MOON_AMBIANCE * moon_chroma) + PERSISTENT_AMBIANCE;

    reflected_light = R_t_r * (
        (1.0 - SUN_AMBIANCE) * sun_chroma * sun_shadow * (light_reflection_factor(norm, dir, sun_dir, k_d, k_s, alpha, voxel_norm, voxel_lighting) /*+
                      light_reflection_factor(norm, dir, normalize(sun_dir + vec3(0.0, 0.1, 0.0)), k_d, k_s, alpha) +
                      light_reflection_factor(norm, dir, normalize(sun_dir - vec3(0.0, 0.1, 0.0)), k_d, k_s, alpha)*/) +
        (1.0 - MOON_AMBIANCE) * moon_chroma * moon_shadow * 1.0 * /*4.0 * */light_reflection_factor(norm, dir, moon_dir, k_d, k_s, alpha, voxel_norm, voxel_lighting)
    );

    /* light = sun_chroma + moon_chroma + PERSISTENT_AMBIANCE;
    diffuse_light =
        sun_chroma * mix(1.0, max(dot(-norm, sun_dir) * 0.5 + 0.5, 0.0), diffusion) +
        moon_chroma * mix(1.0, pow(dot(-norm, moon_dir) * 2.0, 2.0), diffusion) +
        PERSISTENT_AMBIANCE;
    ambient_light = vec3(SUN_AMBIANCE * sun_light + moon_light); */
    return rel_luminance(emitted_light + reflected_light);//rel_luminance(emitted_light + reflected_light);//sun_chroma + moon_chroma + PERSISTENT_AMBIANCE;
}

float get_sun_diffuse2(DirectionalLight sun_info, DirectionalLight moon_info, vec3 norm, vec3 dir, vec3 k_a, vec3 k_d, vec3 k_s, float alpha, vec3 voxel_norm, float voxel_lighting, out vec3 emitted_light, out vec3 reflected_light) {
    return get_sun_diffuse2(sun_info, moon_info, norm, dir, vec3(0.0), vec3(0.0), vec3(1.0), 0.0, k_a, k_d, k_s, alpha, voxel_norm, voxel_lighting, emitted_light, reflected_light);
}

float get_sun_diffuse2(DirectionalLight sun_info, DirectionalLight moon_info, vec3 norm, vec3 dir, vec3 k_a, vec3 k_d, vec3 k_s, float alpha, out vec3 emitted_light, out vec3 reflected_light) {
    return get_sun_diffuse2(sun_info, moon_info, norm, dir, vec3(0.0), vec3(0.0), vec3(1.0), 0.0, k_a, k_d, k_s, alpha, norm, 1.0, emitted_light, reflected_light);
}

// This has been extracted into a function to allow quick exit when detecting a star.
float is_star_at(vec3 dir) {
    float star_scale = 80.0;

    // Star positions
    vec3 pos = (floor(dir * star_scale) - 0.5) / star_scale;

    // Noisy offsets
    pos += (3.0 / star_scale) * /*rand_perm_3*/hash(vec4(pos, 1.0));

    // Find distance to fragment
    float dist = length(normalize(pos) - dir);

    // Star threshold
    if (dist < 0.0015) {
        return 1.0;
    }

    return 0.0;
}

vec3 get_sky_color(vec3 dir, float time_of_day, vec3 origin, vec3 f_pos, float quality, bool with_stars, float refractionIndex, out vec4 clouds) {
#if (CLOUD_MODE == CLOUD_MODE_NONE)
    const bool has_clouds = false;
#elif (CLOUD_MODE == CLOUD_MODE_REGULAR)
    const bool has_clouds = true;
#endif

    if (with_stars || has_clouds) {
        // Sky color
        /* vec3 sun_dir = get_sun_dir(time_of_day);
        vec3 moon_dir = get_moon_dir(time_of_day); */
        vec3 sun_dir = sun_dir.xyz;
        vec3 moon_dir = moon_dir.xyz;

        // sun_dir = sun_dir.z <= 0 ? refract(sun_dir/*-view_dir*/, vec3(0.0, 0.0, 1.0), refractionIndex) : sun_dir;
        // moon_dir = moon_dir.z <= 0 ? refract(moon_dir/*-view_dir*/, vec3(0.0, 0.0, 1.0), refractionIndex) : moon_dir;

        // Add white dots for stars. Note these flicker and jump due to FXAA
        float star = 0.0;
        if (with_stars) {
            vec3 star_dir = normalize(sun_dir * dir.z + cross(sun_dir, vec3(0, 1, 0)) * dir.x + vec3(0, 1, 0) * dir.y);
            star = is_star_at(star_dir);
        }

        // Sun
        const vec3 SUN_SURF_COLOR = vec3(1.5, 0.9, 0.35) * 200.0;

        vec3 sun_halo_color = mix(
            SUN_HALO_DUSK,
            SUN_HALO_DAY,
            max(-sun_dir.z, 0)
        );

        vec3 sun_halo = pow(max(dot(dir, -sun_dir) + 0.1, 0.0), 8.0) * sun_halo_color;
        vec3 sun_surf = pow(max(dot(dir, -sun_dir) - 0.001, 0.0), 3000.0) * SUN_SURF_COLOR * SUN_COLOR_FACTOR;
        vec3 sun_light = (sun_halo + sun_surf) * clamp(dir.z * 10.0, 0, 1);

        // Moon
        const vec3 MOON_SURF_COLOR = vec3(0.7, 1.0, 1.5) * 500.0;
        const vec3 MOON_HALO_COLOR = vec3(0.015, 0.015, 0.05);

        vec3 moon_halo = pow(max(dot(dir, -moon_dir) + 0.1, 0.0), 8.0) * MOON_HALO_COLOR;
        vec3 moon_surf = pow(max(dot(dir, -moon_dir) - 0.001, 0.0), 3000.0) * MOON_SURF_COLOR;
        vec3 moon_light = clamp(moon_halo + moon_surf, vec3(0), vec3(max(dir.z * 3.0, 0)));

        // Replaced all clamp(sun_dir, 0, 1) with max(sun_dir, 0) because sun_dir is calculated from sin and cos, which are never > 1

        vec3 sky_top = mix(
            mix(
                SKY_DUSK_TOP + star / (1.0 + moon_surf * 100.0),
                SKY_NIGHT_TOP + star / (1.0 + moon_surf * 100.0),
                max(pow(sun_dir.z, 0.2), 0)
            ),
            SKY_DAY_TOP,
            max(-sun_dir.z, 0)
        );

        vec3 sky_mid = mix(
            mix( SKY_DUSK_MID,
                SKY_NIGHT_MID,
                max(pow(sun_dir.z, 0.2), 0)
            ),
            SKY_DAY_MID,
            max(-sun_dir.z, 0)
        );

        vec3 sky_bot = mix(
            mix(
                SKY_DUSK_BOT,
                SKY_NIGHT_BOT,
                max(pow(sun_dir.z, 0.2), 0)
            ),
            SKY_DAY_BOT,
            max(-sun_dir.z, 0)
        );

        vec3 sky_color = mix(
            mix(
                sky_mid,
                sky_bot,
                pow(max(-dir.z, 0), 0.4)
            ),
            sky_top,
            max(dir.z, 0)
        );

        // Approximate distance to fragment
        float f_dist = distance(origin, f_pos);

    // Clouds
    #if (CLOUD_MODE == CLOUD_MODE_NONE)
        clouds = vec4(0.0);
    #elif (CLOUD_MODE == CLOUD_MODE_REGULAR)
        clouds = get_cloud_color(dir, origin, time_of_day, f_dist, quality);
        clouds.rgb *= get_sun_brightness(/*sun_dir*/) * (sun_halo * 1.5 + get_sun_color(/*sun_dir*/)) + get_moon_brightness(/*moon_dir*/) * (moon_halo * 80.0 + get_moon_color(/*moon_dir*/) + 0.25);
    #endif

        if (f_dist > 5000.0) {
            sky_color += sun_light + moon_light;
        }
        return mix(sky_color, clouds.rgb, clouds.a);
    } else {
        clouds = vec4(0.0);
        return vec3(0.0);
    }
}

vec3 get_sky_color(vec3 dir, float time_of_day, vec3 origin, vec3 f_pos, float quality, bool with_stars, out vec4 clouds) {
    return get_sky_color(dir, time_of_day, origin, f_pos, quality, with_stars, 1.0, clouds);
}

float fog(vec3 f_pos, vec3 focus_pos, uint medium) {
    return max(1.0 - 5000.0 / (1.0 + distance(f_pos.xy, focus_pos.xy)), 0.0);

    float fog_radius = view_distance.x;
    float mist_radius = 10000000.0;

    float min_fog = 0.5;
    float max_fog = 1.0;

    if (medium == 1u) {
        mist_radius = UNDERWATER_MIST_DIST;
        min_fog = 0.0;
    }

    float fog = distance(f_pos.xy, focus_pos.xy) / fog_radius;
    float mist = distance(f_pos, focus_pos) / mist_radius;

    return pow(clamp((max(fog, mist) - min_fog) / (max_fog - min_fog), 0.0, 1.0), 1.7);
}

/* vec3 illuminate(vec3 color, vec3 light, vec3 diffuse, vec3 ambience) {
    float avg_col = (color.r + color.g + color.b) / 3.0;
    return ((color - avg_col) * light + (diffuse + ambience) * avg_col) * (diffuse + ambience);
} */
vec3 illuminate(float max_light, vec3 view_dir, /*vec3 max_light, */vec3 emitted, vec3 reflected) {
    return emitted + reflected;
    const float NIGHT_EXPOSURE = 10.0;
    const float DUSK_EXPOSURE = 2.0;//0.8;
    const float DAY_EXPOSURE = 1.0;//0.7;

#if (LIGHTING_ALGORITHM == LIGHTING_ALGORITHM_ASHIKHMIN)
    const float DAY_SATURATION = 1.1;
#else
    const float DAY_SATURATION = 1.0;
#endif
    const float DUSK_SATURATION = 0.6;
    const float NIGHT_SATURATION = 0.1;

    const float gamma = /*0.5*//*1.*0*/1.0;//1.0;
    /* float light = length(emitted + reflected);
    float color = srgb_to_linear(emitted + reflected);
    float avg_col = (color.r + color.g + color.b) / 3.0;
    return ((color - avg_col) * light + reflected * avg_col) * (emitted + reflected); */
    // float max_intensity = vec3(1.0);
    vec3 color = emitted + reflected;
    float lum = rel_luminance(color);
    // float lum_sky = lum - max_light;

    /* vec3 sun_dir = get_sun_dir(time_of_day.x);
    vec3 moon_dir = get_moon_dir(time_of_day.x); */
    float sky_light = rel_luminance(
            get_sun_color(/*sun_dir*/) * get_sun_brightness(/*sun_dir*/) * SUN_COLOR_FACTOR +
            get_moon_color(/*moon_dir*/) * get_moon_brightness(/*moon_dir*/));

    // Tone mapped value.
    // vec3 T = /*color*//*lum*/color;//normalize(color) * lum / (1.0 + lum);
    // float alpha = 0.5;//2.0;
    float alpha = mix(
        mix(
            DUSK_EXPOSURE,
            NIGHT_EXPOSURE,
            max(sun_dir.z, 0)
        ),
        DAY_EXPOSURE,
        max(-sun_dir.z, 0)
    );
    vec3 now_light = moon_dir.z < 0 ? moon_dir.xyz : sun_dir.xyz;
    float cos_view_light = dot(-now_light, view_dir);
    // alpha *= exp(1.0 - cos_view_light);
    // sky_light *= 1.0 - log(1.0 + view_dir.z);
    float alph = sky_light > 0.0 && max_light > 0.0 ? mix(1.0 / log(/*1.0*//*1.0 + *//*lum_sky + */1.0 + max_light / (0.0 + sky_light)), 1.0, clamp(max_light - sky_light, 0.0, 1.0)) : 1.0;
    alpha = alpha * min(alph, 1.0);//((max_light > 0.0 && max_light > sky_light /* && sky_light > 0.0*/) ? /*1.0*/1.0 / log(/*1.0*//*1.0 + *//*lum_sky + */1.0 + max_light - (0.0 + sky_light)) : 1.0);
    // alpha = alpha * min(1.0, (max_light == 0.0 ? 1.0 : (1.0 + abs(lum_sky)) / /*(1.0 + max_light)*/max_light));

    vec3 col_adjusted = lum == 0.0 ? vec3(0.0) : color / lum;

    // float L = lum == 0.0 ? 0.0 : log(lum);


    // // float B = T;
    // // float B = L + log(alpha);
    // float B = lum;

    // float D = L - B;

    // float o = 0.0;//log(PERSISTENT_AMBIANCE);
    // float scale = /*-alpha*/-alpha;//1.0;

    // float B_ = (B - o) * scale;

    // // float T = lum;
    // float O = exp(B_ + D);

    float T = 1.0 - exp(-alpha * lum);//lum / (1.0 + lum);
    // float T = lum;

    // Heuristic desaturation
    // const float s = 0.8;
    float s = mix(
        mix(
            DUSK_SATURATION,
            NIGHT_SATURATION,
            max(sun_dir.z, 0)
        ),
        DAY_SATURATION,
        max(-sun_dir.z, 0)
    );
    // s = max(s, (max_light) / (1.0 + s));
    s = max(s, max_light / (1.0 + max_light));

    vec3 c = pow(col_adjusted, vec3(s)) * T;
    // vec3 c = col_adjusted * T;
    // vec3 c = sqrt(col_adjusted) * T;
    // vec3 c = /*col_adjusted * */col_adjusted * T;

    // return color;
    return c;
    // float sum_col = color.r + color.g + color.b;
    // return /*srgb_to_linear*/(/*0.5*//*0.125 * */vec3(pow(color.x, gamma), pow(color.y, gamma), pow(color.z, gamma)));
}