Orkuncakilkaya
6043a67631
The moon was fixed opposite the sun and worth a constant trickle of light. It now carries a phase, 0 new .. 0.5 full .. 1 new again, and that one number decides three things at once: the disc's terminator, the fraction of its light that reaches the ground, and where in the sky it rides. The moon is where the sun was `lag` of a day ago, so a full moon rises as the sun sets and a new moon travels with the sun and is never seen. A new moon is now a properly dark night, which is what makes a carried light worth having. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
84 lines
4.2 KiB
GLSL
84 lines
4.2 KiB
GLSL
in vec2 v_uv;
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out vec4 o_color;
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uniform sampler2D u_sky;
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uniform mat4 u_inv_vp;
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uniform float u_sky_gain;
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uniform float u_sky_sat;
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// a star: one hash per cell of the direction, a few of them bright, a slow twinkle
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float starField(vec3 dir, float t) {
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vec3 p = dir * 230.0;
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vec3 c = floor(p);
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vec3 f = p - c - 0.5;
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float h = fract(sin(dot(c, vec3(12.9898, 78.233, 37.719))) * 43758.5453);
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float h2 = fract(h * 91.7);
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float bright = smoothstep(0.972, 1.0, h);
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float disc = smoothstep(0.42, 0.0, length(f));
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float twinkle = 0.7 + 0.3 * sin(t * (1.5 + 3.0 * h2) + h2 * 40.0);
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return bright * disc * twinkle * (0.5 + h2);
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}
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// The moon: a disc a little over half a degree across, shaded by a terminator taken from
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// its phase, with a few soft maria on it and a halo that opens up when the air is damp.
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// It is the light the night already had (daylight.ludic repoints the sun after dusk) —
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// this is that light finally having something you can look at.
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uniform vec3 u_moon_dir;
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uniform float u_moon_haze; // the weather's overcast: dims the disc, widens the halo
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uniform float u_moon_phase; // 0 new .. 0.5 full .. 1 new
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uniform float u_moon_illum;
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vec3 moonColour(vec3 dir, float night) {
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if (night <= 0.001 || u_moon_dir.y < -0.08) return vec3(0.0);
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float ang = acos(clamp(dot(dir, u_moon_dir), -1.0, 1.0));
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const float R = 0.0096; // about 0.55 degrees
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// the halo first: wide, weak, and thicker through damp air
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float halo = exp(-ang / (R * 6.0)) * (0.02 + 0.35 * u_moon_haze) * u_moon_illum;
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vec3 col = vec3(0.55, 0.60, 0.75) * halo;
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if (ang < R) {
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// where on the disc: a unit offset from its centre, built in the sky's own frame
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vec3 up = abs(u_moon_dir.y) > 0.95 ? vec3(1.0, 0.0, 0.0) : vec3(0.0, 1.0, 0.0);
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vec3 rx = normalize(cross(up, u_moon_dir));
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vec3 ry = cross(u_moon_dir, rx);
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vec2 p = vec2(dot(dir, rx), dot(dir, ry)) / R;
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float r2 = clamp(dot(p, p), 0.0, 1.0);
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// the sphere's normal, and the direction its light comes from, turned by the phase
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vec3 n = vec3(p, sqrt(max(1.0 - r2, 0.0)));
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float a2 = u_moon_phase * 6.28318530718;
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vec3 lit = normalize(vec3(sin(a2), 0.0, -cos(a2)));
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float lam = smoothstep(-0.06, 0.10, dot(n, lit));
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// maria: two or three soft dark blotches, so it is not a flat white circle
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float m = 0.0;
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m += smoothstep(0.34, 0.0, length(p - vec2(-0.28, 0.22)));
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m += 0.7 * smoothstep(0.26, 0.0, length(p - vec2(0.24, -0.10)));
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m += 0.5 * smoothstep(0.20, 0.0, length(p - vec2(0.02, 0.44)));
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float edge = smoothstep(1.0, 0.86, sqrt(r2));
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vec3 disc = mix(vec3(1.0, 0.98, 0.93), vec3(0.62, 0.63, 0.68), clamp(m, 0.0, 1.0));
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// The lit face has to be bright enough to read as the moon and no brighter: the night
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// runs at an exposure of about five, so anything much over one saturates the whole
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// disc to a flat white circle and the terminator disappears. The dark limb keeps a
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// trace of earthshine, which is what makes a crescent look like a sphere.
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col += disc * (lam + 0.010 * (1.0 - lam)) * edge * 0.55;
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}
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return col * night * (1.0 - 0.9 * u_moon_haze);
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}
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void main() {
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vec4 a = u_inv_vp * vec4(v_uv * 2.0 - 1.0, 1.0, 1.0);
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vec3 dir = normalize(a.xyz / a.w - u_cam_pos);
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// level 0: the equirect seam (atan wraps) would otherwise pick the smallest mip along one column
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vec3 col = min(textureLod(u_sky, skyUV(dir), 0.0).rgb, vec3(4096.0)) * u_sky_gain;
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float l = dot(col, vec3(0.2126, 0.7152, 0.0722));
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col = max(mix(vec3(l), col, u_sky_sat), vec3(0.0));
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// the photograph's sky dims with the day (daylight.ludic); the night adds its own
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col *= u_ibl_scale;
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float night = 1.0 - smoothstep(0.0, 0.45, u_daylight);
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if (night > 0.0) {
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vec3 nightCol = mix(vec3(0.012, 0.016, 0.034), vec3(0.003, 0.004, 0.010), clamp(dir.y, 0.0, 1.0));
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float stars = starField(dir, u_time) * smoothstep(-0.02, 0.15, dir.y);
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nightCol += stars * vec3(0.55, 0.6, 0.7) * night;
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col += nightCol * night;
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col += moonColour(dir, night);
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}
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// below the horizon the HDRI ground is replaced by the fog colour
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float below = smoothstep(0.0, -0.08, dir.y);
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vec3 fogCol = skyPrefiltered(vec3(dir.x, 0.02, dir.z), 0.6);
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col = mix(col, fogCol, below);
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o_color = vec4(sane(col), 1.0);
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}
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