#define M_PI 3.1415926535897932384626433832795

 float adsr(float t, vec4 v, float s) {
    v.xyw = max(vec3(2.2e-05), v.xyw);
    float ta = t/v.x;
    float td = max(s, 1.0-(t-v.x)*(1.0-s)/v.y);
    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.;

    const float harmonics = 22.;

    vec2 uv = gl_FragCoord.xy / resolution;

    vec4 pf = texture(pFrameSynth, vec2(uv.x, uv.y + 0.05));
    vec4 vi = texture(iInput0, vec2(uv.x, 1.-uv.y));
    vec4 vi1 = texture(iInput1, vec2(uv.x, uv.y) * 2.);
    vec4 vi2 = texture(iInput2, vec2(uv.x, uv.y) * 2.);
    vec4 vi3 = texture(iInput3, vec2(uv.x, 1.-uv.y) * 4.);

    for (int k = 0; k < 48; k += 1) {
      vec4 data = keyboard[k];

      float kfrq = data.x; // frequency
      float kvel = data.y; // velocity
      float ktim = data.z; // elpased time
      float kchn = data.w; // channel

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

      if (uv.x < 0.25 && uv.x > 0. && kchn == 1.) {
      	float kktim = abs(mod(ktim/2., 2.) - 1.);

      	float u = abs((tanh(ktim / 8.) * (cos(kktim / 4.) / 3.1415)) * 10.275);

        for (float i = 1.; i < harmonics; i += 1.) {
          float amp_1 = ih[int(i) - 1];
          float amp_2 = iha[int(i) - 1];

          float rate = aeb[1];

          float amp = mix(amp_1, amp_2, abs(mod(ktim*rate, 2.) - 1.));

          float att = ih2[int(i) - 1] * u;
          float dec = ih3[int(i) - 1];

          float attack = att;
          float decay = dec;
          float sustain = 0.;
          float release = 0.025;
          float dec_amp = 0.05;
          float env = kvel * adsr(ktim, vec4(attack, decay, sustain, release), dec_amp);
          
          l += fline(kfrq * i) * amp * kvel * env;
          r += fline(kfrq * i) * amp * kvel * env;
        }
      } else if (uv.x < 0.75 && uv.x > 0.5 && kchn == 2.) {
      	float kktim = abs(mod(ktim/2., 2.) - 1.);

      	float u = abs((tanh(ktim / 8.) * (cos(kktim / 4.) / 3.1415)) * 10.275);

        for (float i = 1.; i < harmonics; i += 1.) {
          float amp_1 = pow(ih[(int(i) - 1)], harmonics - i / 1.8);
          float amp_2 = iha[(int(i) - 1)];

          float rate = aeb[1];

          float amp = mix(amp_1, amp_2, abs(mod(kktim*rate*1.5, 2.) - 1.));

          float att = ih2[(int(i) - 1)] / 2.;
          float dec = ih3[(int(i) - 1) % 2] * abs(sin(globalTime * 4.) / 3.1415);

          float attack = att;
          float decay = dec / u;
          float sustain = 0.;
          float release = 0.025;
          float dec_amp = 0.05;
          float env = kvel * adsr(ktim, vec4(attack, decay, sustain, release), dec_amp);

          float env2 = kvel * adsr(ktim, vec4(attack, dec * 8., sustain, release), dec_amp);

          l += fline(kfrq * i) * amp * kvel * env * env2;
          r += fline(kfrq * i) * amp * kvel * env * env2;
        }
      } else if (uv.x < 0.25 && uv.x > 0.5 && kchn == 1.) {
      	float kktim = abs(mod(ktim/2., 2.) - 1.);

      	float u = abs((tanh(ktim / 8.) * (cos(kktim / 4.) / 3.1415)) * 10.275);

        for (float i = 1.; i < harmonics; i += 1.) {
          float amp_1 = pow(ih[(int(i) - 1)], harmonics - i / 2.8);
          float amp_2 = iha[(int(i) - 1)];

          float rate = aeb[1];

          float amp = mix(amp_2, amp_1, abs(mod(kktim*rate*2., 2.) - 1.));

          float att = ih2[(int(i) - 1)] * 4.;
          float dec = ih3[(int(i) - 1) % 2] * abs(sin(globalTime * 4.) / 3.1415);

          float attack = att;
          float decay = dec / u;
          float sustain = 0.;
          float release = 0.025;
          float dec_amp = 0.05;
          float env = kvel * adsr(ktim, vec4(attack, decay, sustain, release), dec_amp);

          float env2 = kvel * adsr(ktim, vec4(attack, dec * 8., sustain, release), dec_amp);

          l += fline(kfrq * i) * amp * kvel * env * env2 * (abs(sin(kktim) / 3.1415) + 0.75);
          l -= vi.r * 0.005;
          l = max(l, 0.);
          r += fline(kfrq * i) * amp * kvel * env * env2 * (abs(cos(kktim) / 3.1415) + 0.95);
          r -= vi.g * 0.005;
          r = max(r, 0.);
        }
      } else if (uv.x < 1. && uv.x > 0.75 && kchn == 3.) {
      	float kktim = abs(mod(ktim/2., 2.) - 1.);

      	float u = abs((tanh(ktim / 8.) * (cos(kktim / 4.) / 3.1415)) * 10.275);

        for (float i = 1.; i < harmonics; i += 1.) {
          float amp_1 = pow(ih[(int(i) - 1)], harmonics - i / 2.8);
          float amp_2 = iha[(int(i) - 1)];

          float rate = aeb[1];

          float amp = mix(amp_2, amp_1, abs(mod(kktim*rate/8., 2.) - 1.));

          float att = ih2[(int(i) - 1)] / 8.;
          float dec = ih3[(int(i) - 1) % 2] * abs(sin(globalTime * 4.) / 3.1415);

          float attack = att;
          float decay = dec / u;
          float sustain = 0.;
          float release = 0.025;
          float dec_amp = 0.05;
          float env = kvel * adsr(ktim, vec4(attack, decay, sustain, release), dec_amp);

          float env2 = kvel * adsr(ktim, vec4(attack, dec * 2., sustain, release), dec_amp);

          l += fline(kfrq * i) * amp * kvel * env * env2 * (abs(sin(kktim) / 3.1415) + 0.75);
          l -= vi.r * 0.005;
          l = max(l, 0.);
          r += fline(kfrq * i) * amp * kvel * env * env2 * (abs(cos(kktim) / 3.1415) + 0.95);
          r -= vi.g * 0.005;
          r = max(r, 0.);
        }
      }
    }

    synthOutput = vec4(l, r, .179, mod(globalTime*(1.+l), 2.) - 1.);
    gl_FragColor = vec4(l*0.125, r*0.125, 0., 1.) * 12. + vi;
  }