Screen buffer: ShowScreenBuffer

       Name: ShowScreenBuffer                                        [Show more]
       Type: Subroutine
   Category: Screen buffer
    Summary: Update the player's scrolling landscape view by copying the
             relevant parts of the screen buffer into screen memory
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawUpdatedObject calls ShowScreenBuffer


 Arguments:

   Y                    The direction of scrolling that we just applied:

                          * 0 = pan right

                          * 1 = pan left

                          * 2 = pan up

                          * 3 = pan down

   toAddr(1 0)          The address of the area in screen memory that we need to
                        update with the contents of the screen buffer


.ShowScreenBuffer

                        \ We start by setting both screenBufferAddr(1 0) and
                        \ fromAddr(1 0) to the address in the screen buffer of
                        \ the content that we need to copy into the screen area
                        \ following the hardware scroll
                        \
                        \ We do this by taking the current value of the address
                        \ in screenBufferAddr(1 0) and applying the change in
                        \ scrollScreen(Hi Lo) for the current pan direction in
                        \ Y, just as we did when we updated the screen address
                        \ in viewScreenAddr(1 0) in the ScrollPlayerView routine

 LDA screenBufferAddr   \ Add scrollScreen(Hi Lo) for this pan direction to the
 CLC                    \ address in screenBufferAddr(1 0), starting with the
 ADC scrollScreenLo,Y   \ low bytes
 STA screenBufferAddr

 STA fromAddr           \ Store the low byte of the result in fromAddr(1 0)

 LDA screenBufferAddr+1 \ And then add the high bytes
 ADC scrollScreenHi,Y
 STA screenBufferAddr+1

 STA fromAddr+1         \ Store the high byte of the result in fromAddr(1 0), so
                        \ fromAddr(1 0) = screenBufferAddr(1 0) and we copy the
                        \ new screen content from the correct address in the
                        \ screen buffer

 CPY #2                 \ If Y >= 2 then we are panning up or down, and we are
 BCS ShowBufferRow      \ scrolling down or up, so jump to ShowBufferRow to
                        \ update the player's scrolling landscape view by
                        \ copying an eight-pixel high character row from the
                        \ screen buffer into screen memory

                        \ Otherwise we are panning left or right, and we are
                        \ scrolling right or left, so fall through into
                        \ ShowBufferColumn to update the player's scrolling
                        \ landscape view by copying a two-pixel wide column from
                        \ the screen buffer into screen memory