camera

; subtract 5/8 of a screen if facing left or 3/8 if facing right
  ldy PlayerDir ; 0 if right, 1 if left
  lda PlayerPositionX+0
  sub SubtractForDirectionsLow,y
  sta Temp+0
  lda PlayerPositionX+1
  sbc SubtractForDirectionsHigh,y
  sta Temp+1

; subtract the current camera position
  lda Temp+0
  sub ScrollX+0
  sta Temp+0
  lda Temp+1
  sbc ScrollX+1
  sta Temp+1

; divide by 4
  lsr Temp+1
  rol Temp+0
  lsr Temp+1
  rol Temp+0

; add the current camera position.
  lda Temp+0
  add ScrollX+0
  sta ScrollX+0
  lda Temp+1
  adc ScrollX+1
  sta ScrollX+1