/*{
  "DESCRIPTION": "Three parallax layers of animated Truchet arcs woven over a glowing plasma backdrop — an endless self-knitting circuit.",
  "CREDIT": "claude-opus-4-8",
  "INPUTS": [
    { "NAME": "scale",  "TYPE": "float", "DEFAULT": 5.0, "MIN": 2.0, "MAX": 12.0 },
    { "NAME": "thick",  "TYPE": "float", "DEFAULT": 0.11, "MIN": 0.03, "MAX": 0.3 },
    { "NAME": "drift",  "TYPE": "float", "DEFAULT": 0.4, "MIN": 0.0, "MAX": 1.5 },
    { "NAME": "hue",    "TYPE": "float", "DEFAULT": 0.55, "MIN": 0.0, "MAX": 1.0 }
  ]
}*/

float hash(vec2 p){
  p = fract(p * vec2(127.1, 311.7));
  p += dot(p, p + 34.5);
  return fract(p.x * p.y * 95.43);
}

vec3 palette(float t){
  return 0.5 + 0.5 * cos(6.28318 * (t + vec3(0.0, 0.33, 0.67) + hue));
}

// one Truchet layer -> vec2(line coverage, flowing pulse)
vec2 truchet(vec2 uv, float scl, float seed){
  uv *= scl;
  vec2 id = floor(uv);
  vec2 f = fract(uv) - 0.5;
  float h = hash(id + seed * 17.0);
  float flip = step(0.5, fract(h + 0.15 * floor(TIME * 0.5 + h * 3.0)));
  if (flip > 0.5) f.x = -f.x;

  float d1 = abs(length(f - vec2(0.5, 0.5)) - 0.5);
  float d2 = abs(length(f - vec2(-0.5, -0.5)) - 0.5);
  float d = min(d1, d2);

  float t = thick * (0.7 + 0.3 * sin(TIME + h * 6.28));
  float line = smoothstep(t, t - 0.045, d);
  float ang = atan(f.y, f.x);
  float pulse = 0.5 + 0.5 * sin(ang * 4.0 - TIME * 3.0 + h * 6.28);
  return vec2(line, pulse);
}

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

  // cohesive backdrop so the weave reads as one fabric, not lines on void
  vec3 col = 0.10 * palette(0.18 * length(uv) - 0.05 * TIME)
                 * (0.6 + 0.4 * sin(uv.x * 3.0 + uv.y * 2.0 + TIME));

  // three layers at increasing scale, parallax-drifting, sharing one palette
  for (int L = 0; L < 3; L++){
    float fl = float(L);
    float scl = scale * (0.7 + 0.55 * fl);
    vec2 off = vec2(0.13, 0.09) * TIME * drift * (fl + 1.0) + fl * 1.7;
    vec2 tr = truchet(uv + off, scl, fl);
    float depth = 1.0 - 0.22 * fl;                 // nearer layers brighter
    vec3 c = palette(0.16 * fl + 0.12 * tr.y + 0.05 * TIME);
    col += tr.x * c * depth * (0.45 + 0.75 * tr.y);
    col += tr.x * 0.12 * depth;                     // core highlight
  }

  col *= 1.0 - 0.25 * dot(uv, uv);                  // vignette
  col = col / (1.0 + 0.6 * col);                    // tonemap layered glow
  col = pow(max(col, 0.0), vec3(0.9));
  gl_FragColor = vec4(col, 1.0);
}