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precision highp float;
varying vec2 vUv;
uniform float time; // seconds, for slow cloud drift
uniform float horizon; // screen-space y of the water horizon (~0.5)
float hash(vec2 p) {
p = fract(p * vec2(123.34, 456.21));
p += dot(p, p + 45.32);
return fract(p.x * p.y);
}
float valueNoise(vec2 p) {
vec2 i = floor(p);
vec2 f = fract(p);
float a = hash(i);
float b = hash(i + vec2(1.0, 0.0));
float c = hash(i + vec2(0.0, 1.0));
float d = hash(i + vec2(1.0, 1.0));
vec2 u = f * f * (3.0 - 2.0 * f);
return mix(mix(a, b, u.x), mix(c, d, u.x), u.y);
}
float fbm(vec2 p) {
float v = 0.0;
float amp = 0.5;
for (int i = 0; i < 4; i++) {
v += amp * valueNoise(p);
p *= 2.0;
amp *= 0.5;
}
return v;
}
const vec3 SKY_HORIZON = vec3(0.80, 0.88, 0.98); // matches water horizon fade
const vec3 SKY_TOP = vec3(0.22, 0.48, 0.86); // deeper zenith blue
const vec3 CLOUD_COLOR = vec3(1.00, 0.98, 0.95); // white, slightly warm
const float DEPTH_BIAS = 0.05; // caps frequency at the horizon (larger = gentler shrink)
const float CLOUD_FREQ = 2.7; // overall cloud scale (larger = more, smaller clouds)
const float X_STRETCH = 0.35; // < 1 stretches clouds horizontally -> wispy
const float CLOUD_THRESH = 0.55; // coverage cutoff; higher = sparser sky
const float CLOUD_SOFT = 0.22; // edge softness of the cloud mask
const float CLOUD_OPACITY = 0.85; // max cloud whiteness
const float DRIFT_SPEED = 0.03; // slow lateral drift (noise units / sec)
const float H_FADE = 0.12; // band over which clouds fade in above horizon
void main() {
// Height above the water horizon: 0 at the waterline, (1 - horizon) at the top.
float above = max(vUv.y - horizon, 0.0);
// Vertical gradient.
float g = clamp(above / (1.0 - horizon), 0.0, 1.0);
vec3 col = mix(SKY_HORIZON, SKY_TOP, pow(g, 0.75));
float haze = 1.0 - smoothstep(0.0, 0.35, g);
col += vec3(0.06, 0.04, 0.00) * haze;
// Flat cloud-ceiling perspective: distance along the view ~ 1/above, so
// features shrink AND compress vertically toward the horizon.
float depth = 1.0 / (above + DEPTH_BIAS);
vec2 q;
q.x = (vUv.x - 0.5) * depth;
q.y = depth;
vec2 p = vec2(q.x * X_STRETCH, q.y) * CLOUD_FREQ;
p.x += time * DRIFT_SPEED;
float n = fbm(p);
float cloud = smoothstep(CLOUD_THRESH, CLOUD_THRESH + CLOUD_SOFT, n);
// Fade clouds into the haze right at the horizon.
cloud *= smoothstep(0.0, H_FADE, above);
col = mix(col, CLOUD_COLOR, cloud * CLOUD_OPACITY);
gl_FragColor = vec4(col, 1.0);
}
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