function init()
  sprites = loadimage('sprites.bmp')
  
  star_scroll = 0
  star_screens = 15
  max_star_scroll = (star_screens - 1) * screen.w
  
  stars = newimage(screen.w * star_screens, screen.h)
  fill(stars, nil, black)
  
  for i = 1, 100 * star_screens do -- 100 stars/screen
    local coord = {math.random(0, stars.w), math.random(0, stars.h)}
    stars[coord] = math.random(dgray, lgray)
  end
  
  -- copy the first "screen" to the last so that we can loop easily
  copy(stars, {0,0,screen.w,screen.h}, stars, {screen.w * (star_screens - 1), 0})
  
  player = {
    loc = {3, 14},
    draw = drawsprite,
    sprite = {image = sprites, rect = {0, 0, 23, 10}},
    update =  function(self)
                self.shot_time = self.shot_time + 1
                simplemove(self)
              end,
    vel = {0, 0},
    shot_time = 0,
  }
  
  bullets = {}
  
  play_keys = {
    down = {
      [keys.up] = moveup,
      [keys.down] = movedown,
      [keys.z] = fire,
      [keys.s] = screenshot,
      [keys.p] = pause,
    },
    up = {
      [keys.down] = stopmoving,
      [keys.up] = stopmoving,
    }
  }
  
  pause_keys = {
    down = { [keys.p] = unpause }
  }
  
  unpause()
end

function moveup() player.vel[2] = -1 end
function movedown() player.vel[2] = 1 end
function stopmoving() player.vel[2] = 0 end

function fire()
  if player.shot_time > 2 then
    local b = {}
    b.loc = {player.loc[1] + 19, player.loc[2] + 4, 4, 1}
    b.draw = drawbullet
    b.color = white
    b.update = simplemove
    b.vel = {3, 0}
    
    table.insert(bullets, b)
    player.shot_time = 0
  end
end

function pause()
  draw = draw_paused
  keymap = pause_keys
  paused_frame = 0
  show_pause_text = true
end

function unpause()
  draw = draw_play
  keymap = play_keys
end

function do_stars()
  if star_scroll < max_star_scroll then
    star_scroll = star_scroll + 1
  else
    star_scroll = 1
  end
  
  copy(stars, {star_scroll,0, screen.w,screen.h}, screen, nil)
end

function do_bullets()
  for i,bullet in pairs(bullets) do
    bullet:update()
    if bullet.loc[1] > screen.w then
      bullets[i] = nil
    else
      bullet:draw()
    end
  end
end

function draw_play()
  player:update()
  do_stars()
  player:draw()
  do_bullets()
end

function draw_paused()
  paused_frame = paused_frame + 1
  
  screen[{23, 24, 50, 8}] = white
  if paused_frame % 5 == 0 then
    show_pause_text = not show_pause_text
  end
  
  if show_pause_text then imageprint(screen, {32,26}, "paused!!") end
end

function drawsprite(self)
  copy(self.sprite.image, self.sprite.rect, screen, self.loc)
end

function simplemove(obj)
  obj.loc[1] = obj.loc[1] + obj.vel[1]
  obj.loc[2] = obj.loc[2] + obj.vel[2]
end

function drawbullet(self)
  screen[self.loc] = white
end