/*{
  "DESCRIPTION": "Neon weave: a two-scale Truchet maze of interlocking glowing tubes with electric colour and a pulse of light flowing along the strands. Hue cycles and the pulse travels so it loops seamlessly. Real-time, 16s loop.",
  "CREDIT": "glslop agent (Claude)",
  "CATEGORIES": ["truchet", "neon", "weave", "maze"],
  "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": "width",  "TYPE": "float", "DEFAULT": 0.07,"MIN": 0.03,"MAX": 0.2 },
    { "NAME": "zoom",   "TYPE": "float", "DEFAULT": 1.0, "MIN": 0.4, "MAX": 2.5 },
    { "NAME": "twoTone","TYPE": "float", "DEFAULT": 0.6, "MIN": 0.0, "MAX": 1.0 }
  ]
}*/

#define PI  3.14159265359
#define TAU 6.28318530718

const float PERIOD = 16.0;

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)));   // electric cyan/magenta/violet
}

float hash(vec2 p){ return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453123); }

// One Truchet layer: returns glow contribution; writes the cell id + arc phase.
vec3 truchet(vec2 uv, float th, float w, float hueoff){
  vec2 cell = floor(uv);
  vec2 f = fract(uv) - 0.5;
  float rnd = hash(cell);
  if (rnd < 0.5) f.x = -f.x;                 // two arc orientations -> connected weave

  // distance to the two quarter-circle arcs (corners (.5,.5) and (-.5,-.5))
  float d1 = abs(length(f - vec2(0.5)) - 0.5);
  float d2 = abs(length(f + vec2(0.5)) - 0.5);
  float d  = min(d1, d2);

  // arc-length parameter along the strand -> a pulse of light travels it (seamless in th)
  vec2 cc = (d1 < d2) ? vec2(0.5) : vec2(-0.5);
  float ang = atan(f.y - cc.y, f.x - cc.x);
  float pulse = 0.6 + 0.4 * sin(ang * 3.0 + (cc.x * 4.0) - th);

  float core = smoothstep(w, w * 0.4, d);    // crisp bright strand
  float halo = w * 0.16 / (d * d + w * 0.10);// tight neon halo
  vec3 c = pal(hue + hueoff + 0.16 * hash(cell + 3.1));
  return c * (core * 1.4 + halo * 0.7) * pulse;
}

void main(){
  vec2 uv = (gl_FragCoord.xy - 0.5 * RENDERSIZE.xy) / RENDERSIZE.y;
  float ph = fract(TIME * speed / PERIOD);
  float th = TAU * ph;

  vec2 p = uv * (3.2 / zoom);
  p = rot(0.15 * sin(th)) * p;               // gentle sway

  vec3 col = vec3(0.0);
  // large weave
  col += truchet(p, th, width, 0.0);
  // finer weave, rotated/offset, blended by twoTone
  col += twoTone * 0.7 * truchet(p * 2.0 + vec2(13.7, 4.2), th + 2.0, width * 1.2, 0.5);

  // white-hot strand cores
  col += vec3(0.9, 0.96, 1.0) * pow(max(max(col.r, col.g), col.b) * 0.5, 3.0) * 0.8;
  col *= glow * 0.85;

  col = col / (1.0 + col);
  col = pow(col, vec3(0.80));
  col *= 1.0 - 0.18 * dot(uv, uv);

  gl_FragColor = vec4(col, 1.0);
}