/*{
  "DESCRIPTION": "Endless flight through a gyroid lattice — shaded shell surfaces with glowing fresnel rims and floating light-orbs in the gaps.",
  "CREDIT": "claude-opus-4-8",
  "INPUTS": [
    { "NAME": "speed",   "TYPE": "float", "DEFAULT": 0.6, "MIN": 0.0, "MAX": 2.0 },
    { "NAME": "density", "TYPE": "float", "DEFAULT": 3.0, "MIN": 1.5, "MAX": 8.0 },
    { "NAME": "glow",    "TYPE": "float", "DEFAULT": 0.8, "MIN": 0.1, "MAX": 1.6 },
    { "NAME": "orbs",    "TYPE": "float", "DEFAULT": 0.9, "MIN": 0.0, "MAX": 2.0 },
    { "NAME": "tint",    "TYPE": "float", "DEFAULT": 0.5, "MIN": 0.0, "MAX": 1.0 }
  ]
}*/

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

float gyroid(vec3 p){ return dot(sin(p), cos(p.yzx)); }

// signed-ish field: negative inside the thin gyroid shells, positive in the gaps
float map(vec3 p){
  return abs(gyroid(p * density)) / density - 0.045;
}

vec3 normal(vec3 p){
  vec2 e = vec2(0.012, 0.0);
  return normalize(vec3(
    map(p + e.xyy) - map(p - e.xyy),
    map(p + e.yxy) - map(p - e.yxy),
    map(p + e.yyx) - map(p - e.yyx)));
}

vec3 palette(float t){
  return 0.5 + 0.5 * cos(6.28318 * (t + vec3(0.0, 0.28, 0.55) + tint));
}

// glow from light-orbs parked off-axis, one per z-slab, accumulated to depth tmax
vec3 orbGlow(vec3 ro, vec3 rd, float tmax){
  vec3 acc = vec3(0.0);
  float t = 0.2;
  for (int i = 0; i < 60; i++){
    if (t > tmax) break;
    vec3 p = ro + rd * t;
    float slab = 4.0;
    float zc = floor(p.z / slab);
    vec2 oc = 1.25 * vec2(sin(zc * 2.1 + 1.0), cos(zc * 1.7));
    vec3 oc3 = vec3(oc, (zc + 0.5) * slab);
    float od2 = dot(p - oc3, p - oc3);
    acc += palette(zc * 0.2 + 0.6) * (0.06 / (0.05 + od2 * od2 * 35.0)) * exp(-t * 0.12);
    t += 0.16;
  }
  return acc;
}

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

  vec3 ro = vec3(0.0, 0.0, TIME * speed);
  vec3 rd = normalize(vec3(uv, 1.25));
  rd.xy *= rot(0.25 * sin(TIME * 0.25));
  rd.xz *= rot(0.20 * cos(TIME * 0.20));

  // small fixed steps to catch the first thin shell (map() isn't a true SDF)
  float t = 0.25, hitT = -1.0;
  for (int i = 0; i < 150; i++){
    if (map(ro + rd * t) < 0.0){ hitT = t; break; }
    t += 0.075;
  }

  vec3 col;
  if (hitT > 0.0){
    vec3 p = ro + rd * hitT;
    vec3 n = normal(p);
    vec3 ld = normalize(vec3(0.5, 0.7, -0.5));
    float diff = 0.35 + 0.65 * max(0.0, dot(n, ld));
    float fres = pow(1.0 - abs(dot(n, rd)), 3.0);

    vec3 base = palette(0.14 * p.z + 0.05 * p.y + 0.05 * TIME);
    col = base * diff;
    col += fres * palette(0.14 * p.z + 0.5) * 1.4 * glow;   // glowing rim
    col *= exp(-hitT * 0.11);                                // depth fade
  } else {
    col = vec3(0.0);
  }

  col += orbGlow(ro, rd, hitT > 0.0 ? hitT : 24.0) * orbs;   // orbs shine through the gaps

  col = col / (1.0 + col);
  col = pow(max(col, 0.0), vec3(0.82));
  gl_FragColor = vec4(col, 1.0);
}