Let's Code MS-DOS 0x19: Fireworks in PowerBasic

firework.bas

$CPU 80286
$LIB EGA ON
$ERROR ALL OFF
$OPTIMIZE SPEED
$COMPILE EXE

defint A-Z

REM =================
REM Global variables
REM =================
dim x#(256)
dim y#(256)
dim x0#(256)
dim y0#(256)
dim vx0#(256)
dim vy0#(256)

active = 1
visible = 0
frame = 1
n = 1
is_exploded = 0
t# = 1.0
dt# = 0.5
g# = 0.00981


sub vsync inline
  REM while (inp(&h3da) and 8) = 1 : wend
  REM while (inp(&h3da) and 8) = 0 : wend
  ! cli
  ! mov dx, &h3da
vsync1:
  ! in al, dx
  ! and al, 8
  ! jnz vsync1
vsync2:
  ! in al, dx
  ! and al, 8
  ! jz vsync2
  ! sti
end sub

sub init_new_rocket( x0#(1), y0#(1), vx0#(1), vy0#(1) )
  x0#(0) = 120.0 + 80.0 * rnd
  y0#(0) = 0
  vx0#(0) = 2.0 * rnd - 1.0
  vy0#(0) = 2.0 * rnd + 1.0
end sub

sub update_particles( x#(1), y#(1), x0#(1), y0#(1), vx0#(1), vy0#(1), t#, n )
  shared g#
  for i = 0 to n - 1
    x#(i) = x0#(i) + vx0#(i) * t#
    y#(i) = y0#(i) + vy0#(i) * t# - 0.5 * g# * t# * t#
  next i
end sub

sub draw_particles(x#(1), y#(1), n, col)
  for i = 0 to n - 1
    pset (x#(i), 199 - y#(i)), col
  next i
end sub

sub init_explosion(x#(1), y#(1), x0#(1), y0#(1), vx0#(1), vy0#(1), n)
  x1# = x#(0)
  y1# = y#(0)
  for i = 0 to n - 1
    v0# = 1.5 * rnd + 0.5
    theta# = 6.283185 * rnd
    x0#(i) = x1#
    y0#(i) = y1#
    vx0#(i) = v0# * cos(theta#)
    vy0#(i) = v0# * sin(theta#)
  next i
end sub

randomize timer
call init_new_rocket(x0#(), y0#(), vx0#(), vy0#())

REM =============
REM Main Program
REM =============
screen 7
do
  call update_particles(x#(), y#(), x0#(), y0#(), vx0#(), vy0#(), t#, n)
  call draw_particles(x#(), y#(), n, (frame mod 15) + 1)
  if frame mod 170 = 0 then
    t# = 0.0
    if is_exploded = 1 then
      is_exploded = 0
      n = 1
      call init_new_rocket(x0#(), y0#(), vx0#(), vy0#())
    else
      is_exploded = 1
      n = 100
      call init_explosion(x#(), y#(), x0#(), y0#(), vx0#(), vy0#(), n)
    end if
  else
    t# = t# + dt#
  end if
  incr frame
  swap active,visible
  screen ,,active,visible
  call vsync
  cls graphics
loop until instat

screen 0