Sunday Under the Leaves

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);
}

float dapple(vec2 p, float sc, float t, float seed, float soft){
  p *= sc;
  vec2 g = floor(p);
  float acc = 0.0;
  for (int j = 0; j < 3; j++) {
    for (int i = 0; i < 3; i++) {
      vec2 c = g + vec2(float(i) - 1.0, float(j) - 1.0);
      float h = hash(c + seed);
      float h2 = hash(c + seed + 7.31);
      vec2 o = vec2(h, h2);
      o += 0.17 * vec2(sin(t * 0.45 + h * 6.283), 0.6 * sin(t * 0.33 + h2 * 6.283));
      vec2 d = p - (c + o);
      float ca = 0.8;
      float sa = 0.6;
      d = vec2(ca * d.x + sa * d.y, -sa * d.x + ca * d.y);
      d.x *= 0.78;
      float r = 0.2 + 0.18 * h2;
      float b = 1.0 - smoothstep(r * soft, r, length(d));
      acc += b * step(0.3, h);
    }
  }
  return acc;
}

void main(){
  vec2 uv = gl_FragCoord.xy / u_resolution;
  vec2 p = (gl_FragCoord.xy - 0.5 * u_resolution) / u_resolution.y;
  float t = u_time;

  vec3 shadeA = vec3(0.30, 0.36, 0.29);
  vec3 shadeB = vec3(0.42, 0.40, 0.31);
  float g = noise(p * 1.6 + vec2(3.1, 1.7));
  vec3 ground = mix(shadeA, shadeB, g);
  float leaf = smoothstep(0.55, 0.8, noise(p * 3.2 + vec2(9.0, 4.0)));
  ground = mix(ground, vec3(0.50, 0.33, 0.20), leaf * 0.45);
  ground *= 0.92 + 0.12 * uv.y;

  float big = dapple(p, 2.6, t, 1.0, 0.25);
  float small = dapple(p + vec2(0.37, 0.11), 5.5, t * 1.15, 4.0, 0.5);
  float L = clamp(big * 0.55 + small * 0.6, 0.0, 1.1);

  vec2 cp = p * 1.1 + vec2(-t * 0.028, -t * 0.009);
  float cl = noise(cp) * 0.65 + noise(cp * 2.1 + 5.0) * 0.35;
  float cloud = smoothstep(0.42, 0.72, cl);
  float sun = mix(1.0, 0.35, cloud);

  vec3 light = vec3(0.98, 0.84, 0.56);
  vec3 col = mix(ground, light * (0.75 + 0.2 * g), clamp(L * sun * 0.82, 0.0, 0.9));

  float glow = smoothstep(1.1, 0.0, length(p - vec2(-0.55, 0.5)));
  col += vec3(0.09, 0.07, 0.03) * glow * sun;
  col = mix(col, col * vec3(0.92, 0.97, 1.02), cloud * 0.5);

  float vig = smoothstep(1.05, 0.35, length(p * vec2(0.85, 1.0)));
  col *= 0.78 + 0.22 * vig;
  col = clamp(col, 0.06, 0.93);
  gl_FragColor = vec4(col, 1.0);
}