/*{
  "DESCRIPTION": "Plasma Globe: branching filaments of electricity arc from a blazing central electrode out to the glass sphere, writhing and forking like a Tesla discharge. Radius-warped radial channels make the tendrils fan and split; they crawl on a circular phase for a seamless 16s loop.",
  "CREDIT": "glslop agent (Claude)",
  "CATEGORIES": ["plasma", "electric", "lightning", "neon", "tesla"],
  "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": "bolts",  "TYPE": "float", "DEFAULT": 9.0,  "MIN": 4.0, "MAX": 18.0 },
    { "NAME": "thin",   "TYPE": "float", "DEFAULT": 0.06, "MIN": 0.02,"MAX": 0.15 },
    { "NAME": "zoom",   "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.6, "MAX": 1.6 }
  ]
}*/

#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(0.0, 0.33, 0.66))); }
float hash(vec2 p){ return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }
float noise(vec2 p){
  vec2 i = floor(p), f = fract(p); f = f * f * (3.0 - 2.0 * f);
  float a = hash(i), b = hash(i + vec2(1, 0)), c = hash(i + vec2(0, 1)), d = hash(i + vec2(1, 1));
  return mix(mix(a, b, f.x), mix(c, d, f.x), f.y);
}

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

  float ph = fract(TIME * speed / PERIOD);
  float th = TAU * ph;
  vec2 orb = vec2(cos(th), sin(th));

  float r = length(uv) + 1e-4;
  float ang = atan(uv.y, uv.x);

  // radius-dependent angular warp -> channels wiggle and fork as they travel out
  float wig = 0.0, amp = 0.55, fr = 1.0;
  for (int i = 0; i < 4; i++){
    wig += amp * noise(vec2(ang * fr * 1.6 + orb.x * fr, r * fr * 3.0 - orb.y * fr + float(i) * 5.0));
    amp *= 0.6; fr *= 2.0;
  }
  // bolt channels: bright where the warped phase hits an integer
  float phase = ang * (bolts / TAU) + (wig - 0.5) * (1.2 + 2.5 * r);   // spread grows with r
  float lane = abs(fract(phase) - 0.5) * 2.0;
  float dep  = floor(phase);

  float bolt = pow(1.0 - lane, 4.0);                 // thin bright filament
  bolt *= smoothstep(thin, thin * 4.0, r);           // hollow at electrode
  // a touch of radial flicker so tendrils break up
  bolt *= 0.6 + 0.6 * noise(vec2(r * 7.0 - orb.y * 2.0, dep * 1.7));

  float radial = exp(-r * 1.4);                      // brighter near centre
  float globe = smoothstep(0.97, 0.90, r);

  vec3 col = vec3(0.0);
  vec3 arc = mix(vec3(0.25, 0.55, 1.0), vec3(0.7, 0.4, 1.0), smoothstep(0.2, 0.95, r));  // blue->violet out
  col += arc * bolt * (0.4 + radial) * globe * 2.4 * glow;
  col += vec3(0.85, 0.92, 1.0) * pow(bolt, 1.8) * (0.4 + radial) * globe * 1.6 * glow;   // white-hot

  // central electrode (small, intense)
  col += vec3(1.0, 0.96, 0.9) * exp(-r * r * 220.0) * 2.0;
  col += vec3(0.5, 0.7, 1.0) * exp(-r * r * 30.0) * 0.5 * glow;

  // glass sphere rim
  float rim = smoothstep(0.86, 0.91, r) * smoothstep(0.97, 0.91, r);
  col += vec3(0.4, 0.6, 1.0) * rim * 0.7 * glow;
  // faint inner glass tint
  col += vec3(0.05, 0.1, 0.2) * globe * (0.2 + 0.3 * radial);

  col = col / (1.0 + col);
  col = pow(col, vec3(0.82));
  col *= 1.0 - 0.16 * dot(uv * zoom, uv * zoom);
  gl_FragColor = vec4(col, 1.0);
}