Keyboard: ToggleJoystick

       Name: ToggleJoystick                                          [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Toggle the joystick setting
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawGunSights calls ToggleJoystick


 Note that the game uses row29_char20_4 to check the joystick status, so it
 is not only an on-screen indicator, it's also the joystick status variable.


.ToggleJoystick

 LDX #&9F               \ Scan the keyboard to see if TAB is being pressed
 JSR ScanKeyboard

 BNE tjoy1              \ If TAB is not being pressed, jump to tjoy1

 LDA pressingTab        \ If pressingTab is non-zero, then we are still pressing
 BNE tjoy3              \ TAB from a previous visit to this routine, so jump to
                        \ tjoy3 to return from the subroutine

                        \ This is a new press of TAB, so now we want to toggle
                        \ the joystick setting

 LDA row29_char20_4     \ Toggle the joystick indicator pixel above the middle
 EOR #%10001000         \ of the rudder indicator
 STA row29_char20_4

 LDA #128               \ Set A = 128 to use as the value for pressingTab below,
                        \ to indicate that TAB is being pressed

 BNE tjoy2              \ Jump to tjoy2 to skip the following instruction (this
                        \ BNE is effectively a JMP as A is never zero)

.tjoy1

 LDA #0                 \ If we get here then TAB is not being pressed, so we
                        \ set A = 0 to set as the value for pressingTab

.tjoy2

 STA pressingTab        \ Set pressingTab to the value in A, which will be 0 if
                        \ TAB is not being pressed, or 128 if it is being
                        \ pressed

.tjoy3

 RTS                    \ Return from the subroutine

 EQUB &8D               \ This byte appears to be unused