program oscilloscope
  use genplotting
  implicit none

  real, dimension(4)    :: frequences

  write (0, '(A)') "----[ genplotting oscilloscope ]----"
  call srand(time())
  call genp_init (0, 'WS/oscilloscope.scratch')

  frequences(1) = 0.86
  frequences(2) = 1.77
  frequences(3) = 1.56
  frequences(4) = 3.04

  call do_oscilloscope(frequences, 1)
  call genp_end (0)
contains
! ---------------------------------------------------------
subroutine plot_axes(amp)
  real, intent(in)     :: amp
  call genp_move(0.0, -amp)
  call genp_draw(0.0,  amp, 7)
  call genp_move(-amp, 0.0)
  call genp_draw( amp, 0.0, 7)
end subroutine
! ---------------------------------------------------------
subroutine plot_a_trace(freq, phy, nbsteps, ypos)
  real, intent(in)        :: freq, phy, ypos
  integer, intent(in)     :: nbsteps

  integer          idx
  real             rstep, px, py
  logical          firstdot

  firstdot = .true.
  do idx=0, nbsteps
    rstep = (real(idx)/real(nbsteps)) 
    px    = -10.0 + (20.0 * rstep)
    py    = ypos + sin(15*(rstep+phy)*freq) 
    if (firstdot) then
      call genp_move(px, py)   ;   firstdot = .false.
    else
      call genp_draw(px, py, 2)
    endif
  enddo

end subroutine
! ---------------------------------------------------------
subroutine do_oscilloscope(freqs, col)
  real, intent(in), dimension(4)   :: freqs
  integer, intent(in)              :: col

  call plot_a_trace(freqs(1), 0.2, 90,  6.66)
  call plot_a_trace(freqs(2), 1.0, 90,  3.33)
  call plot_a_trace(freqs(3), 2.6, 90, -3.33)
  call plot_a_trace(freqs(4), 3.9, 90, -6.66)
  call plot_axes(10.0)

end subroutine
! ---------------------------------------------------------
end program