/*{
  "DESCRIPTION": "Apollonian neon: a fold+inversion Apollonian fractal of nested glowing bubbles, surface-raymarched with electric orbit-trap colour and hot rim light. Slowly breathes and tumbles. Real-time, seamless 16s loop.",
  "CREDIT": "glslop agent (Claude); Apollonian DE after Inigo Quilez",
  "CATEGORIES": ["fractal", "raymarch", "neon", "apollonian"],
  "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": "kparam",    "TYPE": "float", "DEFAULT": 1.25, "MIN": 1.0, "MAX": 1.6 },
    { "NAME": "zoom",      "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.5, "MAX": 2.0 },
    { "NAME": "iterCount", "TYPE": "long",  "DEFAULT": 8,    "MIN": 4,   "MAX": 12 }
  ]
}*/

#define PI  3.14159265359
#define TAU 6.28318530718

const float PERIOD = 16.0;
const int   MAXI   = 12;
const int   STEPS  = 100;

mat2 rot(float a){ float c = cos(a), s = sin(a); return mat2(c, -s, s, c); }

vec3 pal(float t){
  return 0.5 + 0.5 * cos(TAU * (t + vec3(0.0, 0.33, 0.67)));
}

// Apollonian DE (fold into [-1,1] + sphere inversion). orb = orbit trap for colour.
float map(vec3 p, float s, mat2 Rt, out vec4 orb){
  p.xz = Rt * p.xz;                  // rigid tumble (conservative)
  float scale = 1.0;
  orb = vec4(1000.0);
  for (int i = 0; i < MAXI; i++){
    if (i >= iterCount) break;
    p = -1.0 + 2.0 * fract(0.5 * p + 0.5);
    float r2 = dot(p, p);
    orb = min(orb, vec4(abs(p), r2));
    float k = s / r2;
    p *= k;
    scale *= k;
  }
  return 0.25 * abs(p.y) / scale;
}

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

  float ph = fract(TIME * speed / PERIOD);
  float th = TAU * ph;
  float s = kparam + 0.06 * sin(th);          // breathe the packing
  mat2 Rt = rot(0.5 + 0.4 * sin(th));         // rigid tumble (seamless)

  // orbiting camera
  float camDist = 2.6 * zoom;
  float az = th;
  float el = 0.30 + 0.18 * sin(th);
  vec3 ro = camDist * vec3(sin(az) * cos(el), sin(el), cos(az) * cos(el));
  vec3 ta = vec3(0.0);
  vec3 fwd = normalize(ta - ro);
  vec3 rgt = normalize(cross(vec3(0.0, 1.0, 0.0), fwd));
  vec3 upv = cross(fwd, rgt);
  vec3 rd  = normalize(uv.x * rgt + uv.y * upv + 1.5 * fwd);

  // ---- surface raymarch ----
  float t = 0.01;
  float tcap = camDist + 4.0;
  vec4 orb = vec4(1000.0), orbHit = vec4(1000.0);
  float te = 0.0;
  bool hit = false;
  for (int i = 0; i < STEPS; i++){
    vec3 p = ro + rd * t;
    vec4 o;
    float d = map(p, s, Rt, o);
    if (d < 0.0006 * t){ hit = true; orbHit = o; te = t; break; }
    t += d * 0.75;
    if (t > tcap) break;
  }

  vec3 col = vec3(0.0);

  if (hit){
    vec3 p = ro + rd * te;
    vec2 k = vec2(1.0, -1.0);
    float e = 0.0010;
    vec4 o;
    vec3 n = normalize(
      k.xyy * map(p + k.xyy * e, s, Rt, o) +
      k.yyx * map(p + k.yyx * e, s, Rt, o) +
      k.yxy * map(p + k.yxy * e, s, Rt, o) +
      k.xxx * map(p + k.xxx * e, s, Rt, o));

    vec3 lig  = normalize(vec3(0.5, 0.8, 0.4));
    float dif = max(dot(n, lig), 0.0);
    float fres = pow(1.0 - max(dot(n, -rd), 0.0), 2.0);
    float ao  = clamp(1.2 - orbHit.w * 1.6, 0.0, 1.0);  // crevice darkening

    // thin-film iridescence: hue shifts with the orbit trap AND the view angle,
    // so every bubble shimmers oil-slick rainbow toward its rim.
    vec3 base = pal(hue + 0.5 * orbHit.x + 0.35 * orbHit.z + 0.40 * fres);

    col += base * 0.16 * ao;
    col += base * dif * 0.34 * ao;
    col += base * fres * 3.2 * glow;                 // bright iridescent rims
    col += vec3(1.0) * pow(fres, 4.0) * 0.9 * glow;  // hot specular edge
    col *= exp(-0.10 * max(te - camDist + 1.5, 0.0));
  }

  // tone map
  col = col / (1.0 + col);
  col = pow(col, vec3(0.78));
  col *= 1.0 - 0.22 * dot(uv, uv);

  gl_FragColor = vec4(col, 1.0);
}