/*{
  "DESCRIPTION": "Neon gyroid orb: a glowing ball of gyroid minimal-surface lattice (a triply-periodic labyrinth) that breathes and tumbles, lit with electric rim light and an inner energy glow. Real-time, seamless 16s loop.",
  "CREDIT": "glslop agent (Claude)",
  "CATEGORIES": ["gyroid", "raymarch", "neon", "minimal-surface"],
  "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": "thick",  "TYPE": "float", "DEFAULT": 0.55, "MIN": 0.1, "MAX": 1.1 },
    { "NAME": "freq",   "TYPE": "float", "DEFAULT": 5.5,  "MIN": 1.5, "MAX": 8.0 },
    { "NAME": "zoom",   "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.5, "MAX": 2.0 }
  ]
}*/

#define PI  3.14159265359
#define TAU 6.28318530718

const float PERIOD = 16.0;
const int   STEPS  = 120;

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)));
}

// gyroid orb = gyroid slab intersected with a bounding sphere. gv = raw field (colour).
float map(vec3 p, float th, mat2 R1, mat2 R2, float thk, out float gv){
  p.xz = R1 * p.xz;                 // rigid tumble
  p.xy = R2 * p.xy;
  vec3 q = p * freq;
  gv = dot(sin(q), cos(q.yzx));     // gyroid field
  float gyr = (abs(gv) - thk) / freq * 0.6;   // thickened surface (under-stepped)
  float ball = length(p) - 1.7;               // bounding sphere
  return max(gyr, ball);
}

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

  float ph = fract(TIME * speed / PERIOD);
  float th = TAU * ph;
  mat2 R1 = rot(th);                              // one tumble / loop
  mat2 R2 = rot(0.4 + 0.3 * sin(th));
  float thk = thick + 0.18 * sin(th);             // breathe the lattice open/closed

  float camDist = 4.7 * zoom;
  vec3 ro = vec3(0.0, 0.0, camDist);
  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 + 1.6 * fwd);

  // ---- surface raymarch ----
  float t = 0.05;
  float tcap = camDist + 3.6;
  float gvHit = 0.0, te = 0.0;
  bool hit = false;
  for (int i = 0; i < STEPS; i++){
    vec3 p = ro + rd * t;
    float gv;
    float d = map(p, th, R1, R2, thk, gv);
    if (d < 0.0006 * t){ hit = true; gvHit = gv; te = t; break; }
    t += d * 0.6;
    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 = 0.0014, gv;
    vec3 n = normalize(
      k.xyy * map(p + k.xyy * e, th, R1, R2, thk, gv) +
      k.yyx * map(p + k.yyx * e, th, R1, R2, thk, gv) +
      k.yxy * map(p + k.yxy * e, th, R1, R2, thk, gv) +
      k.xxx * map(p + k.xxx * e, th, R1, R2, thk, gv));

    // colour from the gyroid field + radius -> bands of electric colour
    vec3 base = pal(hue + 0.42 * gvHit + 0.5 * length(p));
    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);
    // inner energy glow in the deep channels (where the field is near 0)
    float core = exp(-abs(gvHit) * 2.5);

    col += base * 0.05;                               // near-black body
    col += base * dif * 0.18;
    col += base * fres * 4.2 * glow;                 // bright electric rim
    col += pal(hue + 0.5) * core * 0.9 * glow;       // glowing channel cores
    col += vec3(1.0) * pow(fres, 5.0) * 0.9 * glow;
    col *= exp(-0.22 * max(te - camDist + 2.2, 0.0));
  }

  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);
}