/*{
  "DESCRIPTION": "Solar veil — warm aurora curtains whose rays are combed by a curl-noise flow, draping and rippling like a fire sky.",
  "CREDIT": "claude-opus-4-8",
  "INPUTS": [
    { "NAME": "bands",     "TYPE": "float", "DEFAULT": 3.0, "MIN": 2.0, "MAX": 7.0 },
    { "NAME": "flowAmt",   "TYPE": "float", "DEFAULT": 0.6, "MIN": 0.0, "MAX": 1.5 },
    { "NAME": "intensity", "TYPE": "float", "DEFAULT": 0.9, "MIN": 0.3, "MAX": 1.8 },
    { "NAME": "speed",     "TYPE": "float", "DEFAULT": 0.5, "MIN": 0.0, "MAX": 2.0 }
  ]
}*/

float hash(vec2 p){ p = fract(p * vec2(123.34, 456.21)); p += dot(p, p + 45.32); return fract(p.x * p.y); }
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, 0.0)), c = hash(i + vec2(0.0, 1.0)), d = hash(i + vec2(1.0, 1.0));
  return mix(mix(a, b, f.x), mix(c, d, f.x), f.y);
}
float fbm(vec2 p){ float s = 0.0, a = 0.5; for (int i = 0; i < 3; i++){ s += a * noise(p); p = p * 2.0 + 3.0; a *= 0.5; } return s; }

// flow: mostly vertical (curtain rays) with curl-noise sway
vec2 flow(vec2 p, float t){
  float a = 1.5708 + (fbm(p * 1.6 + vec2(0.0, t * 0.2)) - 0.5) * 3.0 * flowAmt;
  return vec2(cos(a), sin(a));
}

vec3 fire(float h){
  h = clamp(h, 0.0, 1.0);
  vec3 c = mix(vec3(0.05, 0.0, 0.02), vec3(0.6, 0.07, 0.03), smoothstep(0.0, 0.3, h));
  c = mix(c, vec3(1.0, 0.4, 0.05), smoothstep(0.3, 0.6, h));
  c = mix(c, vec3(1.0, 0.85, 0.4), smoothstep(0.6, 0.85, h));
  c = mix(c, vec3(1.0, 1.0, 0.92), smoothstep(0.85, 1.0, h));
  return c;
}

void main(){
  vec2 uv = gl_FragCoord.xy / RENDERSIZE;
  vec2 p = (gl_FragCoord.xy - 0.5 * RENDERSIZE) / RENDERSIZE.y;
  float t = TIME * speed;

  // curtain RAYS: anisotropic vertical streaks (high-x / low-y freq) warped by the flow sway
  float sway = (fbm(vec2(p.x * 1.4, t * 0.25)) - 0.5) * 2.6 * flowAmt;
  float rayX = p.x + sway * 0.45;
  float rays = noise(vec2(rayX * 26.0, p.y * 1.1 - t * 0.6));
  rays += 0.5 * noise(vec2(rayX * 55.0, p.y * 0.8 + t * 0.4));   // finer rays
  rays = pow(clamp(rays * 0.95 - 0.15, 0.0, 1.0), 1.5);
  rays = 0.08 + 1.0 * rays;                         // darker valleys -> rays read as distinct

  // aurora curtains: a few wavy horizontal bands, taller/brighter at the base
  float curtain = 0.0, baseHeat = 0.0;
  for (int i = 0; i < 7; i++){
    if (float(i) >= bands) break;
    float fi = float(i);
    float yC = -0.4 + 0.26 * fi;
    float wob = 0.11 * fbm(vec2(p.x * 1.2 + fi, t * 0.4 + fi * 3.0)) + 0.05 * sin(p.x * 2.5 + t + fi);
    float d = p.y - (yC + wob);
    float c = exp(-abs(d) * 13.0) * smoothstep(0.6, -0.15, d);
    curtain += c;
    baseHeat = max(baseHeat, c * smoothstep(0.1, -0.25, d));   // hottest at the curtain foot
  }

  // night sky + stars
  vec3 col = mix(vec3(0.03, 0.01, 0.04), vec3(0.0, 0.0, 0.015), uv.y);
  col += smoothstep(0.992, 1.0, hash(floor(gl_FragCoord.xy))) * 0.5;

  // warm flowing curtains — hue runs hot (white/yellow) at the base to red at the tips
  float lum = curtain * rays;
  float heat = clamp(0.22 + 1.6 * baseHeat + 0.3 * lum, 0.0, 1.0);
  col += fire(heat) * lum * intensity * 2.0;

  col *= 1.0 - 0.35 * dot(p, p);                    // vignette -> focal curtains
  col = col / (1.0 + col);
  col = pow(max(col, 0.0), vec3(0.9));
  gl_FragColor = vec4(col, 1.0);
}