/*{
  "DESCRIPTION":"Neon dot-lattice corridor: a tiled Menger tunnel flown through with wandering banking, depositing edge-hot neon dots along the invisible folds while surfaces glow with laser-line shading. Seamless 16s loop.",
  "CREDIT":"glslop agent (Claude)",
  "CATEGORIES":["fractal","raymarch","neon","kifs","tunnel"],
  "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":"sway","TYPE":"float","DEFAULT":0.6,"MIN":0.0,"MAX":1.5},
    {"NAME":"zoom","TYPE":"float","DEFAULT":1.0,"MIN":0.5,"MAX":2.0},
    {"NAME":"lens","TYPE":"float","DEFAULT":0.55,"MIN":0.3,"MAX":1.0},
    {"NAME":"iterCount","TYPE":"long","DEFAULT":4,"MIN":2,"MAX":8}
  ]
}*/

#define PI  3.14159265359
#define TAU 6.28318530718

const float PERIOD = 16.0;
const int   MAXI   = 8;
const int   STEPS  = 140;

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(0.55, 0.40, 0.18)));
}

// Menger KIFS tiled infinitely along z (corridor axis).
// d -> surface distance ; trap -> color accumulator ;
// lineT2 -> squared dist to nearest fold axis (laser line) ;
// edge -> peaks where the cell sits on a bar EDGE (dot lattice).
float map(vec3 p, mat2 Rroll, out float trap, out float lineT2, out float edge){
  vec3 z = p;
  z.xy = Rroll * z.xy;
  z.z = mod(z.z + 1.0, 2.0) - 1.0;        // tile period 2 along the shaft
  float scale = 3.0;
  trap = 1.0e9; lineT2 = 1.0e9; edge = 0.0;
  for (int i = 0; i < MAXI; i++){
    if (i >= iterCount) break;
    z = abs(z);
    if (z.x < z.y) z.xy = z.yx;
    if (z.x < z.z) z.xz = z.zx;
    if (z.y < z.z) z.yz = z.zy;
    z = z * scale - vec3(2.0);
    if (z.z < -1.0) z.z += 2.0;
    trap   = min(trap, dot(z, z));
    lineT2 = min(lineT2, min(min(dot(z.xy, z.xy), dot(z.yz, z.yz)), dot(z.xz, z.xz)));
  }
  vec3 q = abs(z);
  float c1 = max(q.x, max(q.y, q.z));
  float c3 = min(q.x, min(q.y, q.z));
  float mid = q.x + q.y + q.z - c1 - c3;
  edge = smoothstep(0.86, 0.99, mid);
  return length(max(q - vec3(1.0), 0.0)) * pow(scale, -float(iterCount));
}

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

  float ph = fract(TIME * speed / PERIOD);
  float th = TAU * ph;
  float flyZ = 2.0 * ph;                   // advance exactly one tile per loop -> seamless
  mat2 Rroll = rot(0.35 * sway * sin(th));

  // corridor camera: straight down the shaft with wandering sway (Parent 1's
  // shaft + Parent 2's meander).
  vec3 ro = vec3(0.45 * sway * sin(th) + 0.18 * sway * sin(3.0 * th),
                 0.30 * sway * sin(2.0 * th),
                 flyZ);
  vec3 ta = ro + vec3(0.12 * sway * cos(th),
                      0.08 * sway * cos(2.0 * th),
                      1.0);
  vec3 fwd = normalize(ta - ro);
  vec3 rgt = normalize(cross(vec3(0.0, 1.0, 0.0), fwd));
  vec3 upv = cross(fwd, rgt);
  float roll = 0.22 * sway * sin(th);
  // fisheye lens (Parent 2): ray angle grows with screen radius.
  float rr = length(uv);
  float theta = rr * lens * PI;
  vec2 dir2 = rr > 1.0e-5 ? uv / rr : vec2(0.0, 1.0);
  vec3 baseRd = dir2.x * rgt + dir2.y * upv;
  vec3 rd = normalize(cos(theta) * fwd + sin(theta) * (baseRd));
  // barrel roll on the lateral basis
  rd = normalize((baseRd.x * cos(roll) - baseRd.y * sin(roll)) * rgt +
                 (baseRd.x * sin(roll) + baseRd.y * cos(roll)) * upv +
                 cos(theta) * fwd);

  // ---- fly-THROUGH with surface deposit: accumulate edge-dots AND shade the
  // first solid hit with laser-line lighting. Blends Parent 1 surfaces with
  // Parent 2 dot-lattice glow. ----
  float t = 0.02;
  float tcap = 14.0;
  float trans = 1.0;
  vec3 col = vec3(0.0);
  float trap, lineT2, edge;
  float prevD = 1.0e9;
  float trapHit = 1.0e9, lineHit2 = 1.0e9, te = 0.0;
  bool hit = false;

  for (int i = 0; i < STEPS; i++){
    vec3 p = ro + rd * t;
    float tr, l2, ed;
    float d = map(p, Rroll, tr, l2, ed);
    // surface hit (Parent 1)
    if (!hit && d < 0.0006 * t){ hit = true; trapHit = tr; lineHit2 = l2; te = t; }
    // edge-dot deposit on zero-crossing of the (invisible) shell (Parent 2)
    if (prevD < 0.0 && d >= 0.0 && trans > 0.001){
      vec3 body = pal(hue + 0.6 * sqrt(tr) + 0.10 * (t + flyZ));
      float dotGlow = pow(ed, 2.0);
      col += trans * body * dotGlow * glow * 1.4;
      trans *= 1.0 - 0.7 * dotGlow;
    }
    if (!hit) t += max(d, 0.002) * 0.7; else t += 0.02;
    prevD = d;
    if (t > tcap) break;
  }

  if (hit){
    vec3 p = ro + rd * te;
    vec2 k = vec2(1.0, -1.0);
    float e = 0.0014, tr, l2, ed;
    vec3 n = normalize(
      k.xyy * map(p + k.xyy * e, Rroll, tr, l2, ed) +
      k.yyx * map(p + k.yyx * e, Rroll, tr, l2, ed) +
      k.yxy * map(p + k.yxy * e, Rroll, tr, l2, ed) +
      k.xxx * map(p + k.xxx * e, Rroll, tr, l2, ed));
    vec3 body = pal(hue + 0.6 * sqrt(trapHit) + 0.10 * (te + flyZ));
    vec3 lig  = normalize(vec3(0.3, 0.6, 0.74));
    float dif = max(dot(n, lig), 0.0);
    float fres = pow(1.0 - max(dot(n, -rd), 0.0), 2.0);
    float laser = 1.0 / (1.0 + 120.0 * lineHit2);
    laser = pow(laser, 1.5);
    vec3 laserCol = mix(vec3(0.85, 0.96, 1.0), body + 0.3, 0.4);
    col += trans * (body * 0.05 + dif * body * 0.18 + fres * laserCol * glow * 0.6 + laser * laserCol * glow * 1.2);
  }

  col = col / (1.0 + col);                 // soft tonemap
  col = pow(col, vec3(0.85));
  gl_FragColor = vec4(col, 1.0);
}