float adsr(float t, vec4 v, float s) {
  v.xyw = max(vec3(2.2e-05), v.xyw);
  // attack term
  float ta = t/v.x;
  // decay / sustain amplitude term
  float td = max(s, 1.0-(t-v.x)*(1.0-s)/v.y);
  // length / release term
  float tr = (1.0 - max(0.0,t-(v.x+v.y+v.z))/v.w);
  return max(0.0, min(ta, tr*td));
}

void main () {
  float l = 0.;
  float r = 0.;

  vec2 uv = gl_FragCoord.xy / resolution;

  vec4 t = texture(iInput0, vec2(globalTime * 16. + uv.x, uv.y));
  vec4 f = texture(pFrame, vec2(uv.x, uv.y+(sin(globalTime * 64.)/3.1415/6644.)));

  float attenuation_constant = 1.95;

  const float harmonics = 62.;

  vec4 arr[8] = vec4[8](vec4(0.75, 0.25, 0., 0.), vec4(0.75, 0.5, 0., 0.), vec4(0.2, 0.72, 0., 0.), vec4(0.2, 0.75, 0., 0.),
                        vec4(0.57, 0.2, 0., 0.), vec4(0., 0.75, 0., 0.), vec4(0.25, 0.5, 0., 0.), vec4(0.25, 0.5, 0., 0.));

  for (int k = 0; k < 8; k += 1) {
    vec4 data = keyboard[k];

    float kfrq = data.x;
    float kvel = data.y;
    float ktim = data.z;
    float kchn = data.w;

    vec3 pdata = pKey[0];

    float pkfrq = pdata.x;
    float pkvel = pdata.y;
    float pktim = pdata.z;

    if (kfrq == 0.) {
      break;
    }

    if (kchn == 0. && uv.x < 0.5) {
      vec4 t = texture(iInput0, vec2(ktim/8.,uv.y));
      float kktim = abs(mod(ktim*8., 2.) - 1.);
      kfrq = mix(pkfrq, kfrq, min(ktim *49. + sin(ktim)*16., 1.));

      float u = abs((tanh(ktim * 62.) * (cos(ktim * 64.) / 3.1415)) * .75);

      for (float i = 1.; i < harmonics; i += (2.)) {
        float a = 1. / pow(i - u, attenuation_constant * 0.805);

        float a2 = 1. / (pow(i, attenuation_constant * (0.06555+ abs(sin(kktim*8./i/(sin(globalTime / 180.))))*10.5)) / tan(kktim * ((i/(abs(sin(globalTime / 64.)) / 100.)) / 2.)));

        float mix_f = 0.5 * (1. - abs(tan(kktim/8.+1.4/cos((i*8.) - i / 18.) - 1.)));

        vec4 lc = arr[int(i+7. + globalTime * 64.) % 8];

        float attack = .25 + abs(sin(i * mix_f) / 8.);
        float decay = 1. / mix_f * i/8.;
        float sustain = 0.;
        float release = 8.25;
        float decay_amp = 0.35;
        float env = kvel * adsr(ktim, vec4(attack, decay, sustain, release), decay_amp);

        float al = mix(a, a2, mix_f);

        l += fline(kfrq * i) * (al * env)*a*lc.r;
        r += fline(kfrq * i) * (al * env)*a*lc.g;
      }
    } else if (kchn == 1. && uv.x > 0.5) {
      vec4 t = texture(iInput0, vec2(ktim/ 4.,uv.y));
      float kktim = abs(mod(ktim*20., 2.) - 1.);
      kfrq = mix(pkfrq, kfrq, min(ktim * 19. + sin(ktim)*16., 1.));

      float u = abs((tanh(ktim / 4.) * (cos(ktim * 8.) / 3.1415)) * 10.18);

      for (float i = 1.; i < harmonics; i += (1.+u)) {
        float a = 1. / pow(i, attenuation_constant * 0.905);

        float a2 = 1. / (pow(i, attenuation_constant * (0.86555 * u)) / (sin(kktim / (i / 64.))));

        float mix_f = 0.5 * (1. - abs(sin(kktim*8.+1.8*cos(i * a * 18.) - 1.)));

        vec4 lc = arr[int(i+7. + globalTime * 2.) % 8];

        float attack = .25 * mix_f* (harmonics-i*2.+kktim/8.) / 8.;
        float decay = 1. * mix_f / -i*2.;
        float sustain = 0.;
        float release = 8.25;
        float decay_amp = 0.35;
        float env = kvel * adsr(kktim, vec4(attack, decay, sustain, release), decay_amp);

        float al = mix(a, a2, mix_f);

        l += fline(kfrq * i) * (al * env)*a*lc.r;
        r += fline(kfrq * i) * (al * env)*a*lc.g;
      }
    }
  }

  vec4 fo = max(f - 0.005, 0.);

  gl_FragColor = vec4(l, r, l + r, 1.) + fo;
  synthOutput = vec4(l, r, (l + r) / 2., 0.) + fo; // WebGL 2.0 only
}