/*{
  "DESCRIPTION": "A spiral cluster of blobby gem-spheres, orbited by the camera and shaded with thin-film iridescence keyed to view angle and world height rather than density -- so the hue stays vivid instead of collapsing to mud. Exact loop: one full camera turn and one full cluster spin per period.",
  "CREDIT": "glslop",
  "CATEGORIES": ["Raymarch", "3D", "Generative"],
  "INPUTS": [
    { "NAME": "blend", "TYPE": "float", "DEFAULT": 0.38, "MIN": 0.15, "MAX": 0.6 },
    { "NAME": "spinTurns", "TYPE": "float", "DEFAULT": 1.0, "MIN": 0.0, "MAX": 3.0 },
    { "NAME": "camDist", "TYPE": "float", "DEFAULT": 2.6, "MIN": 1.8, "MAX": 4.0 }
  ]
}*/

#define STEPS 90
#define GEMS 7
#define PI 3.14159265359
#define PERIOD 8.0

vec3 rotY(vec3 p, float a){
  float c = cos(a), s = sin(a);
  return vec3(c*p.x + s*p.z, p.y, -s*p.x + c*p.z);
}

float smin(float a, float b, float k){
  float h = clamp(0.5 + 0.5*(b - a)/k, 0.0, 1.0);
  return mix(b, a, h) - k*h*(1.0 - h);
}

float sdSphere(vec3 p, vec3 c, float r){
  return length(p - c) - r;
}

float map(vec3 p, float spinAngle){
  vec3 pr = rotY(p, -spinAngle);
  float d = sdSphere(pr, vec3(0.0), 0.42);
  for (int i = 0; i < GEMS; i++){
    float a = (float(i) / float(GEMS)) * 2.0 * PI;
    float rise = 0.28 * sin(a * 2.0);
    vec3 c = vec3(cos(a) * 1.05, rise, sin(a) * 1.05);
    float r = 0.3 + 0.06 * cos(a * 3.0);
    d = smin(d, sdSphere(pr, c, r), blend);
  }
  return d;
}

vec3 normalAt(vec3 p, float spinAngle){
  vec2 e = vec2(0.002, 0.0);
  return normalize(vec3(
    map(p + e.xyy, spinAngle) - map(p - e.xyy, spinAngle),
    map(p + e.yxy, spinAngle) - map(p - e.yxy, spinAngle),
    map(p + e.yyx, spinAngle) - map(p - e.yyx, spinAngle)
  ));
}

vec3 filmColor(float ph){
  ph = fract(ph);
  return 0.5 + 0.5 * cos(2.0 * PI * (ph + vec3(0.0, 0.33, 0.67)));
}

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

  float ph = fract(TIME / PERIOD);
  float orbitAngle = 2.0 * PI * ph;
  float spinAngle = 2.0 * PI * ph * spinTurns;

  vec3 ro = vec3(sin(orbitAngle) * camDist, 0.55, cos(orbitAngle) * camDist);
  vec3 target = vec3(0.0);
  vec3 fwd = normalize(target - ro);
  vec3 right = normalize(cross(fwd, vec3(0.0, 1.0, 0.0)));
  vec3 up = cross(right, fwd);
  vec3 rd = normalize(fwd * 1.7 + uv.x * right + uv.y * up);

  float t = 0.0;
  float hit = -1.0;

  for (int i = 0; i < STEPS; i++){
    vec3 p = ro + rd * t;
    float d = map(p, spinAngle);
    if (d < 0.001){
      hit = t;
      break;
    }
    t += d;
    if (t > 12.0) break;
  }

  vec3 col = vec3(0.015, 0.015, 0.03);

  if (hit > 0.0){
    vec3 p = ro + rd * hit;
    vec3 n = normalAt(p, spinAngle);
    float vDotN = clamp(dot(-rd, n), 0.0, 1.0);
    float filmPhase = vDotN * 1.6 + p.y * 1.4 + ph;
    vec3 base = filmColor(filmPhase);

    vec3 lightDir = normalize(vec3(0.5, 0.8, -0.4));
    float diff = clamp(dot(n, lightDir), 0.0, 1.0);
    float fres = pow(1.0 - vDotN, 3.0);

    vec3 shaded = base * (0.3 + 0.7 * diff) + fres * vec3(1.0);
    float fog = exp(-0.12 * hit);
    col = mix(col, shaded, fog);
  }

  col = col / (1.0 + col);
  col = pow(col, vec3(0.4545));

  gl_FragColor = vec4(col, 1.0);
}