/*{
  "DESCRIPTION": "Handheld dream: morphing lava-lamp metaballs rendered the way a 1989 dot-matrix LCD would have shown them - a low virtual resolution, four shades of swamp-green, and 8x8 ordered (Bayer) dithering standing in for every gradient, complete with the faint grid between liquid-crystal cells. The blobs orbit closed loops for a seamless retro loop.",
  "CREDIT": "glslop agent (Claude)",
  "CATEGORIES": ["pixel-art", "dithering", "retro", "gameboy", "metaballs"],
  "INPUTS": [
    { "NAME": "speed",  "TYPE": "float", "DEFAULT": 1.0,   "MIN": 0.0, "MAX": 3.0 },
    { "NAME": "res",    "TYPE": "float", "DEFAULT": 150.0, "MIN": 48.0, "MAX": 300.0 },
    { "NAME": "blobs",  "TYPE": "long",  "DEFAULT": 5,     "MIN": 2,   "MAX": 7 },
    { "NAME": "spread", "TYPE": "float", "DEFAULT": 1.25,  "MIN": 0.5, "MAX": 1.6 },
    { "NAME": "grid",   "TYPE": "float", "DEFAULT": 0.5,   "MIN": 0.0, "MAX": 1.0 }
  ]
}*/

#define PI  3.14159265359
#define TAU 6.28318530718
const float PERIOD = 16.0;

// recursive ordered (Bayer) dither, no bitwise ops
float bayer2(vec2 a){ a = floor(a); return fract(a.x*0.5 + a.y*a.y*0.75); }
float bayer4(vec2 a){ return bayer2(0.5*a)*0.25 + bayer2(a); }
float bayer8(vec2 a){ return bayer4(0.5*a)*0.25 + bayer2(a); }

void main(){
  float pxSize = RENDERSIZE.y / res;
  vec2 pc = floor(gl_FragCoord.xy / pxSize);                 // virtual pixel coords
  vec2 uv = (2.0*(pc*pxSize + 0.5*pxSize) - RENDERSIZE.xy) / RENDERSIZE.y;

  float ph = fract(TIME * speed / PERIOD);
  float th = TAU * ph;

  // morphing metaballs on closed orbits
  float field = 0.0;
  for(int k = 0; k < 7; k++){
    if(k >= int(blobs)) break;
    float fk = float(k);
    float om = (mod(fk, 2.0) < 0.5) ? 1.0 : 2.0;             // integer turns -> loop
    float R  = (0.34 + 0.15*fk) * spread;
    float ph2 = fk*2.39996;
    vec2  c  = R*vec2(cos(om*th + ph2), sin(om*th*1.0 - ph2*1.3));
    vec2  d  = uv - c;
    field += (0.060 + 0.012*fk) / (dot(d,d) + 0.035);
  }
  field = smoothstep(0.5, 2.1, field);                        // shape the blob falloff

  // dithered quantization to 4 levels
  float lv = clamp(floor(field*3.0 + bayer8(pc)), 0.0, 3.0);

  // Game Boy DMG palette
  vec3 g0 = vec3(0.06, 0.22, 0.06);
  vec3 g1 = vec3(0.19, 0.39, 0.13);
  vec3 g2 = vec3(0.55, 0.67, 0.06);
  vec3 g3 = vec3(0.61, 0.74, 0.06);
  vec3 col = lv < 0.5 ? g0 : (lv < 1.5 ? g1 : (lv < 2.5 ? g2 : g3));

  // faint LCD cell grid between virtual pixels
  vec2 sub = fract(gl_FragCoord.xy / pxSize);
  float line = min(smoothstep(0.0, 0.08, sub.x) * smoothstep(0.0, 0.08, sub.y),
                   smoothstep(0.0, 0.08, 1.0 - sub.x) * smoothstep(0.0, 0.08, 1.0 - sub.y));
  col *= 1.0 - 0.18 * grid * (1.0 - line);

  // slight green-screen vignette
  vec2 vv = (2.0*gl_FragCoord.xy - RENDERSIZE.xy) / RENDERSIZE.y;
  col *= 1.0 - 0.12 * dot(vv, vv);

  gl_FragColor = vec4(col, 1.0);
}