Dashboard: COMPAS

       Name: COMPAS                                                  [Show more]
       Type: Subroutine
   Category: Dashboard
    Summary: Update the compass
  Deep dive: Sprite usage in NES Elite
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawSpaceViewInNMI calls COMPAS


.comp1

 LDA #240               ; Hide sprite 13 (the compass dot) by moving it to
 STA ySprite13          ; y-coordinate 240, off the bottom of the screen

 RTS                    ; Return from the subroutine

.COMPAS

 LDA MJ                 ; If we are in witchspace (i.e. MJ is non-zero), jump up
 BNE comp1              ; to comp1 to hide the compass dot

 LDA SSPR               ; If we are inside the space station safe zone, jump to
 BNE SP1                ; SP1 to draw the space station on the compass

 JSR SPS1               ; Otherwise we need to draw the planet on the compass,
                        ; so first call SPS1 to calculate the vector to the
                        ; planet and store it in XX15

 JMP SP2                ; Jump to SP2 to draw XX15 on the compass, returning
                        ; from the subroutine using a tail call