/*{
  "DESCRIPTION": "Eternal Return: a Droste-style infinite zoom. Glowing orbs are arranged on a logarithmic-spiral lattice that scales into itself forever, rotating and rushing inward down a neon wormhole that never ends. Self-similar scaling makes the zoom seamless over a 16s loop.",
  "CREDIT": "glslop agent (Claude)",
  "CATEGORIES": ["droste", "spiral", "infinite-zoom", "neon", "hypnotic"],
  "INPUTS": [
    { "NAME": "speed",   "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.0, "MAX": 3.0 },
    { "NAME": "glow",    "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.3, "MAX": 3.0 },
    { "NAME": "hue",     "TYPE": "float", "DEFAULT": 0.0,  "MIN": 0.0, "MAX": 1.0 },
    { "NAME": "arms",    "TYPE": "long",  "DEFAULT": 5,    "MIN": 2,   "MAX": 12 },
    { "NAME": "twist",   "TYPE": "float", "DEFAULT": 2.2,  "MIN": 0.5, "MAX": 5.0 },
    { "NAME": "zoom",    "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.6, "MAX": 1.8 }
  ]
}*/

#define PI  3.14159265359
#define TAU 6.28318530718

const float PERIOD = 16.0;

vec3 pal(float t){ return 0.5 + 0.5 * cos(TAU * (t + vec3(0.0, 0.33, 0.66))); }

void main(){
  vec2 uv = (gl_FragCoord.xy - 0.5 * RENDERSIZE.xy) / RENDERSIZE.y;
  uv /= zoom;

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

  float r = length(uv) + 1e-4;
  float a = atan(uv.y, uv.x);

  float lr = log(r);
  // logarithmic-spiral lattice: couple angle & log-radius
  float arm   = a * float(arms) / TAU + lr * twist;       // spiral arm coordinate
  float ringF = lr * float(arms) * 0.5;                   // log-spaced rings (self-similar)

  // scroll inward one ring per loop (self-similar -> seamless zoom) + rotate
  float fa = fract(arm - ph);
  float fr = fract(ringF - ph);
  float depth = floor(ringF - ph);

  // thin crisp line families: concentric rings x spiral arms
  float w = 0.010;
  float ringLine = pow(w / (abs(fr - 0.5) * abs(fr - 0.5) + w), 1.7);
  float armLine  = pow(w / (abs(fa - 0.5) * abs(fa - 0.5) + w), 1.7);
  float node     = ringLine * armLine;                   // bright intersection nodes

  // cohesive colour: smooth radial gradient (static) + seamless time cycle -> no seam pops
  vec3 cBase = pal(hue + ph + 0.22 * lr);

  float fade = smoothstep(0.0, 0.10, r) * smoothstep(1.4, 0.25, r);

  vec3 col = vec3(0.0);
  col += cBase * (ringLine + armLine) * 0.7 * fade * glow;  // glowing spiral grid on black
  col += vec3(0.9, 0.96, 1.0) * node * 1.4 * fade * glow;   // white-hot lattice nodes

  // deep throat glow at the centre
  col += pal(hue + ph + 0.3) * exp(-r * 7.0) * 0.8 * glow;

  col = col / (1.0 + col);
  col = pow(col, vec3(0.82));
  col *= 1.0 - 0.12 * dot(uv * zoom, uv * zoom);
  gl_FragColor = vec4(col, 1.0);
}