/*{
  "DESCRIPTION": "Signal Lost: a corrupted-video transmission. A neon broadcast test-pattern is torn apart by datamosh block-displacement, RGB channel shear, scanlines, dropout bands and posterized colour. The corruption stutters and rolls on integer cycles for a seamless 16s loop.",
  "CREDIT": "glslop agent (Claude)",
  "CATEGORIES": ["glitch", "datamosh", "vhs", "corruption", "neon"],
  "INPUTS": [
    { "NAME": "speed",  "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.0, "MAX": 3.0 },
    { "NAME": "amount", "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.0, "MAX": 2.0 },
    { "NAME": "hue",    "TYPE": "float", "DEFAULT": 0.0,  "MIN": 0.0, "MAX": 1.0 },
    { "NAME": "shear",  "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.0, "MAX": 2.0 },
    { "NAME": "zoom",   "TYPE": "float", "DEFAULT": 1.0,  "MIN": 0.6, "MAX": 1.8 }
  ]
}*/

#define PI  3.14159265359
#define TAU 6.28318530718

const float PERIOD = 16.0;

vec3 pal(float t){ return 0.5 + 0.5 * cos(TAU * (t + vec3(0.0, 0.33, 0.66))); }
float hash(float x){ return fract(sin(x * 127.13) * 43758.5453); }
float hash2(vec2 p){ return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }

// the clean source image: a neon broadcast test pattern
vec3 source(vec2 uv){
  vec2 p = uv;
  vec3 c = pal(hue + floor((p.x * 0.5 + 0.5) * 8.0) / 8.0);   // vertical colour bars
  float r = length(p);
  c = mix(c, vec3(1.0, 0.95, 0.2), smoothstep(0.012, 0.0, abs(r - 0.45)));   // ring
  c = mix(c, vec3(0.05), smoothstep(0.012, 0.0, abs(r - 0.22)));             // inner ring
  c = mix(c, vec3(1.0), smoothstep(0.02, 0.0, min(abs(p.x), abs(p.y)) - 0.0) * step(r, 0.5)); // crosshair
  float grid = step(0.92, max(sin(p.x * 40.0), sin(p.y * 40.0)));
  c = mix(c, c * 1.6, grid * 0.3);
  return c;
}

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

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

  // discrete "frame" of the corruption (stutters; rolls back at the seam)
  float frame = floor(ph * 12.0);
  float roll  = ph;                                  // vertical roll

  vec2 guv = uv;
  guv.y = fract(guv.y * 0.5 + 0.5 + roll) * 2.0 - 1.0;   // rolling sync

  // block-displacement tears: some horizontal bands jump sideways
  float band = floor(guv.y * 22.0);
  float bseed = hash(band + frame * 31.0);
  float tear = step(0.72, bseed) * (hash(band * 2.3 + frame) - 0.5) * 0.7 * amount;
  guv.x += tear;

  // occasional full dropout band -> noise static
  float drop = step(0.93, hash(band * 1.7 + frame * 5.0));

  // RGB channel shear (chromatic break-up), worse in torn bands
  float ca = (0.006 + 0.05 * step(0.72, bseed)) * shear;
  vec3 col;
  col.r = source(guv + vec2(ca, 0.0)).r;
  col.g = source(guv).g;
  col.b = source(guv - vec2(ca, 0.0)).b;

  // posterize colour (quantization artefact)
  col = floor(col * 6.0) / 6.0;

  // dropout static
  float st = hash2(floor(guv * vec2(80.0, 50.0)) + frame);
  col = mix(col, vec3(st), drop * amount);

  // scanlines + bright sync line
  col *= 0.75 + 0.25 * sin(gl_FragCoord.y * 2.2);
  float sync = smoothstep(0.02, 0.0, abs(fract(guv.y * 0.5 + 0.5 + roll * 3.0) - 0.5));
  col += sync * 0.25;

  // value crush + slight bloom on hot colours
  col = clamp(col, 0.0, 1.0);
  col += pow(max(col - 0.6, 0.0), vec3(1.5)) * 0.6;

  col *= 1.0 - 0.18 * dot(uv * zoom, uv * zoom);
  gl_FragColor = vec4(col, 1.0);
}