/*{
  "DESCRIPTION": "Liquid chrome swells with thin-film interference — hue rides the reflection phase, not density. Seamless 8s loop.",
  "INPUTS": [
    { "NAME": "speed", "TYPE": "float", "DEFAULT": 1.0, "MIN": 0.25, "MAX": 3.0 },
    { "NAME": "film",  "TYPE": "float", "DEFAULT": 1.0, "MIN": 0.3,  "MAX": 2.5 }
  ]
}*/

#define PERIOD 8.0
#define TAU 6.28318530718

// analytic heightfield: few large travelling swells, integer temporal multiples for a clean loop
// returns vec3(height, dH/dx, dH/dy)
vec3 field(vec2 p, float ph){
  vec3 h = vec3(0.0);
  vec2 d1 = normalize(vec2( 0.83,  0.55));
  vec2 d2 = normalize(vec2(-0.42,  0.91));
  vec2 d3 = normalize(vec2( 0.31, -0.95));

  float s;
  s = 2.1*dot(d1,p) - TAU*1.0*ph + 0.0;  h.x += 0.55*sin(s); h.yz += 0.55*2.1*cos(s)*d1;
  s = 3.4*dot(d2,p) + TAU*2.0*ph + 1.7;  h.x += 0.34*sin(s); h.yz += 0.34*3.4*cos(s)*d2;
  s = 5.9*dot(d3,p) - TAU*3.0*ph + 4.1;  h.x += 0.16*sin(s); h.yz += 0.16*5.9*cos(s)*d3;
  return h;
}

// procedural environment: deep sky with wide luminous reflector bands
vec3 env(vec3 rd){
  float up = clamp(rd.y*0.5+0.5, 0.0, 1.0);
  vec3 sky = mix(vec3(0.004,0.005,0.010), vec3(0.035,0.05,0.09), pow(up,1.8));
  float az = atan(rd.z, rd.x);
  float el = rd.y;
  // narrow luminous strips on a mostly-void sphere — the chrome stays dark between streaks
  vec3 band = vec3(0.0);
  band += vec3(2.6, 0.60, 0.10) * smoothstep(0.14,0.015,abs(el-0.34)) * pow(0.5+0.5*sin(az*2.0+0.4), 3.0);
  band += vec3(0.10, 0.95, 2.8) * smoothstep(0.12,0.012,abs(el+0.02)) * pow(0.5+0.5*sin(az*3.0-1.2), 3.0);
  band += vec3(1.2, 1.15, 1.4) * smoothstep(0.06,0.008,abs(el-0.64));
  band += vec3(1.8, 0.2, 2.4)  * smoothstep(0.11,0.012,abs(el+0.42)) * pow(0.5+0.5*sin(az+2.6), 3.0);
  return sky + band;
}

// thin-film interference: RGB phases from optical path difference
vec3 filmColor(float opd){
  vec3 phase = TAU * opd * vec3(1.0, 1.22, 1.46);
  return 0.5 + 0.5*cos(phase + vec3(0.0, 2.1, 4.2));
}

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

  // circular-orbit domain drift — loop-safe
  vec2 orb = 0.35*vec2(cos(TAU*ph), sin(TAU*ph));
  vec2 p = uv*2.0 + orb;

  vec3 H = field(p, ph);
  vec3 n = normalize(vec3(-H.y, 1.35, -H.z));

  // grazing camera so the mirror dominates
  vec3 vd = normalize(vec3(uv.x*0.55, -0.85, uv.y*0.55 + 0.55));
  vec3 rd = reflect(vd, n);

  float cosT = clamp(abs(dot(vd, n)), 0.0, 1.0);
  float fres = pow(1.0 - cosT, 2.0);

  vec3 reflection = env(rd);

  // broad iridescence: optical path from film thickness x incidence, plus a slow spatial drift
  float opd = film * (1.9*cosT + 0.35*H.x);
  vec3 irid = filmColor(opd);

  // flow mask: interference lives on the swell crests and steep slopes; flats stay chrome-dark
  float slope = length(H.yz);
  float crest = smoothstep(0.25, 1.0, H.x);
  float flow = clamp(0.7*crest + 0.6*smoothstep(1.0, 2.4, slope), 0.0, 1.0);

  // chrome: dark mirror everywhere, interference painted along the flow
  vec3 col = reflection * mix(vec3(1.0), irid*1.9, flow);
  col += irid * fres * (0.25 + 0.75*flow) * 0.9;
  col += vec3(0.9,0.95,1.0) * pow(max(rd.y,0.0), 24.0) * 0.8;   // sky glint

  // valleys sink to the void
  float valley = smoothstep(0.5, -1.0, H.x);
  col *= mix(1.0, 0.10, valley*0.85);

  col *= 1.0 - 0.35*dot(uv,uv);

  // soft highlight knee
  vec3 hot = max(col - 1.0, 0.0);
  col = min(col, 1.0) + hot/(1.0+hot);

  gl_FragColor = vec4(col, 1.0);
}