窓辺の小雨粒

precision mediump float;
uniform vec2 u_resolution;
uniform float u_time;

float hash(vec2 p){
  return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453);
}

float noise(vec2 p){
  vec2 i = floor(p);
  vec2 f = fract(p);
  f = f * f * (3.0 - 2.0 * f);
  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));
  return mix(mix(a, b, f.x), mix(c, d, f.x), f.y);
}

vec3 scene(vec2 p){
  float t = u_time * 0.025;
  float x = p.x + t;
  vec3 sky = vec3(0.72, 0.75, 0.76);
  vec3 mid = vec3(0.47, 0.54, 0.52);
  vec3 low = vec3(0.35, 0.37, 0.41);
  float h = 0.12 + 0.14 * noise(vec2(x * 2.2, 1.0));
  vec3 c = mix(low, mid, smoothstep(-0.36, -0.14, p.y));
  c = mix(c, sky, smoothstep(h - 0.08, h + 0.08, p.y));
  float colm = noise(vec2(x * 5.0, 3.0));
  float blk = smoothstep(0.4, 0.7, colm) * (1.0 - smoothstep(h - 0.1, h + 0.1, p.y)) * smoothstep(-0.3, 0.0, p.y);
  c = mix(c, c * 0.82 + vec3(0.02, 0.03, 0.0), blk);
  for (int i = 0; i < 5; i++) {
    float fi = float(i);
    float bx = mod(hash(vec2(fi, 2.0)) * 2.4 - t, 2.4) - 1.2;
    vec2 c0 = vec2(bx, -0.14 + 0.2 * hash(vec2(fi, 5.0)));
    float b = 1.0 - smoothstep(0.03, 0.09, length(p - c0));
    c = mix(c, vec3(0.86, 0.66, 0.38), b * 0.5);
  }
  return c;
}

void main(){
  vec2 uv = gl_FragCoord.xy / u_resolution;
  vec2 p = (gl_FragCoord.xy - 0.5 * u_resolution) / u_resolution.y;
  vec3 base = scene(p);
  vec3 col = mix(base, vec3(0.78, 0.8, 0.8), 0.14);

  const float GRID = 9.0;
  vec2 g = p * GRID;
  vec2 id = floor(g);
  vec2 f = fract(g) - 0.5;
  float h1 = hash(id);
  float h2 = hash(id + 7.3);
  float h3 = hash(id + 13.1);
  float life = fract(u_time * 0.035 + h3);
  float grow = smoothstep(0.0, 0.15, life) * (1.0 - smoothstep(0.6, 1.0, life));
  float r = (0.12 + 0.16 * h1) * grow * step(0.35, h2);
  vec2 o = vec2(h2 - 0.5, h1 - 0.5) * 0.35;
  vec2 d = f - o;
  d.y *= 1.1;
  float dist = length(d);
  float m = 1.0 - smoothstep(r - 0.08, r, dist);

  vec2 q = p - (d / GRID) * 3.0;
  vec3 dc = scene(q) * 1.06 + 0.03;
  float rim = smoothstep(r - 0.12, r, dist);
  float lowSide = clamp(-d.y / max(r, 0.001) * 1.5 + 0.3, 0.0, 1.0);
  dc = mix(dc, dc * 0.68, rim * lowSide);
  float hl = 1.0 - smoothstep(0.0, 0.08, length(d - vec2(-0.35, 0.4) * r));
  dc += 0.22 * hl * step(0.05, r);
  col = mix(col, dc, m);

  float sh = (1.0 - smoothstep(0.0, 0.12, abs(dist - r - 0.03))) * step(0.0, -d.y) * step(0.05, r);
  col *= 1.0 - 0.06 * sh * (1.0 - m);

  float v = smoothstep(1.1, 0.3, length((uv - 0.5) * vec2(1.2, 1.0)));
  col *= 0.86 + 0.14 * v;
  gl_FragColor = vec4(col, 1.0);
}