The CheckForSamePanKey subroutine - The Sentinel on the BBC Micro

       Name: CheckForSamePanKey                                      [Show more]
       Type: Subroutine
   Category: Keyboard
    Summary: Check to see whether the same pan key is being held down compared
             to the last time we checked
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawLandscapeView (Part 2 of 3) calls CheckForSamePanKey
             * ProcessGameplay calls CheckForSamePanKey


 Returns:

   Z flag               Determines whether the same pan key is being held down
                        compared to the last time we checked:

                          * Z flag will be set if the same pan key is being held
                            down (so a BEQ branch will be taken)

                          * Z flag will be clear otherwise (so a BNE branch will
                            be taken)


.CheckForSamePanKey

 SEI                    \ Disable interrupts so the key logger doesn't get
                        \ updated while we check it for pan key presses

 LDY #3                 \ Scan the keyboard for the first four game keys ("S",
 JSR ScanForGameKeys    \ "D", "L" and ",", for pan left, right up and down)

 LDA latestPanKeyPress  \ Set A to the key logger value of the latest pan key
                        \ press, which will either be a current key press or the
                        \ value from the last pan key press to be made

 CMP keyLogger          \ Compare with the key logger entry for "S" and "D"
                        \ (pan left and right)

 BEQ cpan1              \ If the key logger entry is unchanged from the previous
                        \ pan key press in latestPanKeyPress, then the same pan
                        \ key is being held down, so jump to cpan1 with the
                        \ Z flag set accordingly

 CMP keyLogger+2        \ Compare with the key logger entry for "L" and ","
                        \ (pan up and down), so the Z flag will be set if the
                        \ same pan key is being held down

.cpan1

 CLI                    \ Re-enable interrupts

 RTS                    \ Return from the subroutine

[X]

Subroutine ScanForGameKeys (category: Keyboard)

Scan for game key presses and update the key logger

[X]

Label cpan1 is local to this routine

[X]

Variable keyLogger in workspace Main variable workspace

The four-byte key logger for logging game key presses

[X]

Variable latestPanKeyPress in workspace Main variable workspace

The key logger value of the latest pan key press, which will either be a current key press or the value from the last pan key press to be made

Keyboard: CheckForSamePanKey