/*{
  "DESCRIPTION": "Living labyrinth: a Turing-style reaction-diffusion maze of meandering ridges, like brain coral or a fingerprint, rendered bioluminescent - dark teal canyons with glowing cyan ridge-lines and magenta where channels pinch off. The pattern slowly reorganises, ridges branching and merging, then returns to its start for a seamless loop.",
  "CREDIT": "glslop agent (Claude)",
  "CATEGORIES": ["reaction-diffusion", "turing", "coral", "organic", "pattern"],
  "INPUTS": [
    { "NAME": "speed",  "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.0, "MAX": 3.0 },
    { "NAME": "scale",  "TYPE": "float", "DEFAULT": 3.0,  "MIN": 1.0, "MAX": 6.0 },
    { "NAME": "density","TYPE": "float", "DEFAULT": 14.0, "MIN": 8.0, "MAX": 36.0 },
    { "NAME": "glow",   "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.3, "MAX": 2.5 }
  ]
}*/

#define PI  3.14159265359
#define TAU 6.28318530718
const float PERIOD = 16.0;

float hash(vec2 p){ return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }
float vnoise(vec2 p){
  vec2 i = floor(p), f = fract(p);
  f = f*f*(3.0 - 2.0*f);
  float a = hash(i), b = hash(i+vec2(1,0)), c = hash(i+vec2(0,1)), d = hash(i+vec2(1,1));
  return mix(mix(a,b,f.x), mix(c,d,f.x), f.y);
}
float fbm(vec2 p){
  float s = 0.0, a = 0.5;
  for(int i = 0; i < 5; i++){ s += a*vnoise(p); p = p*2.02 + 7.3; a *= 0.5; }
  return s;
}

void main(){
  vec2 uv = (2.0*gl_FragCoord.xy - RENDERSIZE.xy) / RENDERSIZE.y;
  vec2 p = uv * scale;

  float ph = fract(TIME * speed / PERIOD);
  float th = TAU * ph;

  // orbiting sample offset -> field morphs and returns; integer phase drift -> ridges flow
  vec2 off = 0.42*vec2(cos(th), sin(th));
  float field = fbm(p + off) + 0.35*fbm(p*2.1 - off*1.6 + 4.0);

  float v = sin(field*density - 2.0*th);              // contour ridges, drifting
  float ridge = abs(v);

  // thin glowing ridge lines where v crosses zero
  float line = glow * 0.13 / (ridge*ridge + 0.010);
  // soften the canyon floors
  float floorShade = smoothstep(0.0, 0.7, ridge);

  vec3 canyon = vec3(0.012, 0.06, 0.075);
  vec3 ridgeC = vec3(0.25, 0.95, 0.85);              // cyan ridge
  vec3 pinch  = vec3(1.0, 0.22, 0.55);               // magenta where channels pinch

  // pinch-off accent: glowing nodes where the broad field crests (channels crowd)
  float crest = pow(max(0.0, 1.0 - ridge*2.0), 3.0);
  float pinchAmt = smoothstep(0.62, 1.05, fbm(p*1.7 + off));

  vec3 col = canyon * (0.5 + 0.8*floorShade);
  col += mix(ridgeC, pinch, pinchAmt) * line;        // ridge lines tint magenta in pinch zones
  col += pinch * crest * pinchAmt * 1.6 * glow;      // bright magenta pinch nodes
  col += ridgeC * crest * (1.0 - pinchAmt) * 0.7 * glow;

  // faint depth shading from the broad field
  col *= 0.7 + 0.5*smoothstep(0.2, 1.4, field);

  col *= 1.0 - 0.16*dot(uv, uv);
  col = col / (1.0 + col);
  col = pow(col, vec3(0.85));
  gl_FragColor = vec4(col, 1.0);
}