Shooter game - Code Golf

-- Game start

tweens.bullet_y = 180
var_s_bullet_x = 0

var_zone = 15

var_s_target_a_x = math.random(-200,200)
var_s_target_a_y = math.random(-200,200)

function ship_pos()
 var_ms_ship_x_pos = wm_tag(-{sax})*19
end

function bullet()
 wm_schedule {
   { action='tween', tween='bullet_y', from=180, to=-250, duration=1, easing=linear },
 }
end

var_ms_score = 0

function on_millisecond(dt)
 ship_pos()
  if (var_s_target_a_x >= (var_ms_ship_x_pos - var_zone) and var_s_target_a_x <= (var_ms_ship_x_pos + var_zone)) then
   var_ms_x_hit = 1
  else
   var_ms_x_hit = 0
  end
 if (var_s_target_a_y >= (tweens.bullet_y - var_zone) and var_s_target_a_y <= (tweens.bullet_y + var_zone)) then
  var_ms_y_hit = 1
 else
  var_ms_y_hit = 0
 end
 if (var_ms_x_hit == 1 and var_ms_y_hit == 1) then
  var_ms_score = var_ms_score + 1
  wm_vibrate(1,30)
  bullet()
 end
 if (var_s_target_a_x >= (var_ms_ship_x_pos - var_zone) and var_s_target_a_x <= (var_ms_ship_x_pos + var_zone) and var_s_target_a_y > 160 ) then
  var_ms_score = var_ms_score - 5
  wm_vibrate(1,50)
 end
end

function on_second(h,m,s)
  if s%3==0 then
   var_s_target_a_x = math.random(-200,200)
   var_s_target_a_y = math.random(-200,200)
  end
 var_s_bullet_x = var_ms_ship_x_pos
 bullet()
end

function on_display_bright()
 var_ms_score = 0
end

var_highscore = 0
function on_display_not_bright()
 if var_ms_score > var_highscore then
   var_highscore = var_ms_score
 end
end