; Gated, Retriggerable Envelope Generator UDO (adsr140)
; Based on design of Doepfer A-140 Envelope Generator Module
; Code based on ADSR code by Nigel Redmon 
; (http://www.earlevel.com/main/2013/06/03/envelope-generators-adsr-code/)
; Example by Steven Yi (2015.02.08)

opcode adsr140_calc_coef, k, kk
  
  knum_samps, kratio xin
  xout exp( -log((1.0 + kratio) / kratio) / knum_samps)
    
endop

/* Gated, Re-triggerable ADSR modeled after the Doepfer A-140 */
opcode adsr140, a, aakkkk

agate, aretrig, kattack, kdecay, ksustain, krelease xin

kstate init 0  ; 0 = attack, 1 = decay, 2 = sustain
klasttrig init -1
kval init 0.0
asig init 0
kindx = 0

kattack_base init 0
kdecay_base init 0
krelease_base init 0

kattack_samps init 0
kdecay_samps init 0
krelease_samps init 0

kattack_coef init 0
kdecay_coef init 0
ksustain_coef init 0

klast_attack init -1
klast_decay init -1
klast_release init -1

if (klast_attack != kattack) then
  klast_attack = kattack
  kattack_samps = kattack * sr
  kattack_coef = adsr140_calc_coef(kattack_samps, 0.3)
  kattack_base = (1.0 + 0.3) * (1 - kattack_coef)
endif

if (klast_decay != kdecay) then
  klast_decay = kdecay
  kdecay_samps = kdecay * sr
  kdecay_coef = adsr140_calc_coef(kdecay_samps, 0.0001)
  kdecay_base = (ksustain - 0.0001) * (1.0 - kdecay_coef)
endif

if (klast_release != krelease) then
  klast_release = krelease
  krelease_samps = krelease * sr
  krelease_coef = adsr140_calc_coef(krelease_samps, 0.0001)
  krelease_base =  -0.0001 * (1.0 - krelease_coef)
endif


while (kindx < ksmps) do
  if (agate[kindx] > 0) then
    kretrig = aretrig[kindx]
    if (kretrig > 0 && klasttrig <= 0) then
      kstate = 0
    endif
    klasttrig = kretrig

    if (kstate == 0) then
      kval = kattack_base + (kval * kattack_coef)
      if(kval >= 1.0) then
        kval = 1.0
        kstate = 1
      endif
      asig[kindx] = kval

    elseif (kstate == 1) then
      kval = kdecay_base + (kval * kdecay_coef)
      if(kval <= ksustain) then
        kval = ksustain
        kstate = 2
      endif
      asig[kindx] = kval 

    else
      asig[kindx] = ksustain
    endif

  else ; in a release state
    kstate = 0
    if (kval == 0.0) then
      asig[kindx] = 0
    else 
    ; releasing
      kval = krelease_base + (kval * krelease_coef)
    if(kval <= 0.0) then
      kval = 0.0
    endif
    asig[kindx] = kval  
    endif

  endif

  kindx += 1
od

xout asig

endop