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#version 330
uniform vec2 resolution;
uniform vec3 camera_forward;
uniform vec3 camera_right;
uniform vec3 camera_up;
uniform vec3 sun_direction;
uniform vec3 horizon_colour;
uniform vec3 zenith_colour;
uniform float day_amount;
uniform float twilight_amount;
uniform float tan_half_fovy;
out vec4 finalColor;
void
main() {
vec2 ndc = gl_FragCoord.xy / resolution * 2.0 - 1.0;
float aspect_ratio = resolution.x / resolution.y;
vec3 view_direction = normalize(
camera_forward +
camera_right * ndc.x * aspect_ratio * tan_half_fovy +
camera_up * ndc.y * tan_half_fovy
);
float height = smoothstep(-0.20, 0.80, view_direction.y);
float horizon = 1.0 - smoothstep(0.0, 0.35, abs(view_direction.y));
vec3 sky = mix(horizon_colour, zenith_colour, height);
float sun_alignment = dot(view_direction, sun_direction);
float sun_facing = max(sun_alignment, 0.0);
float sun_facing_2 = sun_facing * sun_facing;
float sun_facing_4 = sun_facing_2 * sun_facing_2;
sky += vec3(0.65, 0.16, 0.035) *
horizon * twilight_amount * sun_facing_4;
float sun_wide = smoothstep(0.9510565, 0.9986295, sun_alignment);
float sun_core = smoothstep(0.9925462, 0.9998477, sun_alignment);
float moon_alignment = -sun_alignment;
float moon_wide = smoothstep(0.9702957, 0.9993908, moon_alignment);
float moon_core = smoothstep(0.9961947, 0.9999619, moon_alignment);
float sun_visibility = smoothstep(-0.12, 0.04, sun_direction.y);
float moon_visibility = smoothstep(-0.10, 0.04, -sun_direction.y);
vec3 sun_glow_colour = mix(
vec3(1.00, 0.82, 0.38),
vec3(1.00, 0.25, 0.035),
twilight_amount
);
vec3 moon_glow_colour = vec3(0.32, 0.46, 0.82);
float sun_glow =
(sun_wide * 0.13 + sun_core * 0.32) * sun_visibility;
float moon_glow =
(moon_wide * 0.08 + moon_core * 0.17) *
moon_visibility * (1.0 - day_amount);
sky += (1.0 - sky) * sun_glow_colour * sun_glow;
sky += (1.0 - sky) * moon_glow_colour * moon_glow;
finalColor = vec4(clamp(sky, 0.0, 1.0), 1.0);
}
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