/*{
  "DESCRIPTION": "Persistent liquid-chrome ribbons stirred by orbiting vortices.",
  "INPUTS": [
    { "NAME": "motion", "TYPE": "float", "DEFAULT": 1.0, "MIN": 0.0, "MAX": 2.5 },
    { "NAME": "swirl", "TYPE": "float", "DEFAULT": 1.0, "MIN": 0.0, "MAX": 2.0 },
    { "NAME": "trail", "TYPE": "float", "DEFAULT": 0.986, "MIN": 0.94, "MAX": 0.999 },
    { "NAME": "hueShift", "TYPE": "float", "DEFAULT": 0.08, "MIN": 0.0, "MAX": 1.0 }
  ],
  "PASSES": [
    { "TARGET": "paint", "PERSISTENT": true, "FLOAT": true },
    {}
  ]
}*/

#define TAU 6.28318530718

vec3 palette(float t) {
  return 0.5 + 0.5 * cos(TAU * (t + hueShift + vec3(0.00, 0.29, 0.57)));
}

vec2 vortex(vec2 p, vec2 center, float spin) {
  vec2 d = p - center;
  float influence = exp(-dot(d, d) * 13.0);
  return vec2(-d.y, d.x) * influence * spin;
}

void main() {
  vec2 uv = isf_FragNormCoord;

  if (PASSINDEX == 0) {
    float t = TIME * motion;
    float frameStep = min(TIMEDELTA * 60.0, 2.0);
    vec2 p = uv - 0.5;
    p.x *= RENDERSIZE.x / RENDERSIZE.y;

    vec2 a = vec2(0.27 * cos(t * 0.41), 0.24 * sin(t * 0.53));
    vec2 b = vec2(0.25 * cos(t * 0.37 + 3.1), 0.28 * sin(t * 0.46 + 2.2));
    vec2 vel = vortex(p, a, 2.1) + vortex(p, b, -1.8);
    vel += vec2(
      sin(TAU * uv.y * 2.0 + t * 0.4),
      cos(TAU * uv.x * 2.0 - t * 0.3)
    ) * 0.055;
    vel *= swirl;
    vel.x /= RENDERSIZE.x / RENDERSIZE.y;

    vec2 back = uv - vel * (0.014 * frameStep * motion);
    vec2 px = 1.0 / RENDERSIZE;
    vec3 old = IMG_NORM_PIXEL(paint, back).rgb * 0.70;
    old += IMG_NORM_PIXEL(paint, back + vec2(px.x, 0.0)).rgb * 0.075;
    old += IMG_NORM_PIXEL(paint, back - vec2(px.x, 0.0)).rgb * 0.075;
    old += IMG_NORM_PIXEL(paint, back + vec2(0.0, px.y)).rgb * 0.075;
    old += IMG_NORM_PIXEL(paint, back - vec2(0.0, px.y)).rgb * 0.075;
    old *= pow(trail, frameStep);

    vec2 dropA = p - a;
    vec2 dropB = p - b;
    float injectA = smoothstep(0.046, 0.0, length(dropA));
    float injectB = smoothstep(0.040, 0.0, length(dropB));
    vec2 cpos = vec2(0.18 * sin(t * 0.68), 0.30 * cos(t * 0.29));
    float injectC = smoothstep(0.034, 0.0, length(p - cpos));
    vec3 fresh = palette(t * 0.035 + length(a) + 0.12) * injectA;
    fresh += palette(t * 0.035 + length(b) + 0.62) * injectB;
    fresh += palette(t * 0.035 + length(cpos) + 0.36) * injectC;

    float boundary = smoothstep(0.0, 0.03, uv.x)
                   * smoothstep(0.0, 0.03, 1.0 - uv.x)
                   * smoothstep(0.0, 0.03, uv.y)
                   * smoothstep(0.0, 0.03, 1.0 - uv.y);
    vec3 next = max(old, fresh * 0.72) * boundary;
    gl_FragColor = vec4(clamp(next, 0.0, 2.0), 1.0);
  } else {
    vec2 uv2 = isf_FragNormCoord;
    vec2 px = 1.0 / RENDERSIZE;
    vec3 c = IMG_THIS_PIXEL(paint).rgb;
    float l = dot(c, vec3(0.3333));
    float lx = dot(IMG_NORM_PIXEL(paint, uv2 + vec2(px.x, 0.0)).rgb, vec3(0.3333));
    float ly = dot(IMG_NORM_PIXEL(paint, uv2 + vec2(0.0, px.y)).rgb, vec3(0.3333));
    vec2 grad = vec2(lx - l, ly - l);
    float rim = clamp(length(grad) * 28.0, 0.0, 1.0);

    vec3 chrome = c * (0.34 + 1.35 * l);
    chrome += rim * palette(0.16 + l * 0.22) * 0.72;
    chrome += pow(max(l, 0.0), 3.0) * vec3(0.8, 0.9, 1.0);
    chrome = chrome / (1.0 + 0.65 * chrome);
    gl_FragColor = vec4(chrome, 1.0);
  }
}