Screen buffer: SetBufferAddress

       Name: SetBufferAddress                                        [Show more]
       Type: Subroutine
   Category: Screen buffer
    Summary: Set screenBufferAddr(1 0) to the address from which the interrupt
             handler should fetch new content to scroll onto the screen
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawUpdatedObject calls SetBufferAddress


 Arguments:

   Y                    The direction of scrolling that we are applying:

                          * 0 = pan right

                          * 1 = pan left

                          * 2 = pan up

                          * 3 = pan down


.SetBufferAddress

 LDA screenBufferLo,Y   \ Set screenBufferAddr(1 0) to the Y-th entry from the
 STA screenBufferAddr   \ screenBufferHi and screenBufferLo lookup tables
 LDA screenBufferHi,Y   \
 STA screenBufferAddr+1 \ This sets screenBufferAddr(1 0) to the address from
                        \ which the interrupt handler should start pulling
                        \ screen content to scroll onto the screen, so:
                        \
                        \   * When panning right: The left column of the
                        \     column-shaped screen buffer appears first as the
                        \     new content scrolls in from the right
                        \
                        \   * When panning left: The right column of the
                        \     column-shaped screen buffer appears first as the
                        \     new content scrolls in from the right
                        \
                        \   * When panning up: The bottom row of the row-shaped
                        \     screen buffer appears first as the new content
                        \     scrolls in from above
                        \
                        \   * When panning down: The top row of the row-shaped
                        \     screen buffer appears first as the new content
                        \     scrolls in from below
                        \
                        \ So this sets screenBufferAddr(1 0) to the address
                        \ where the interrupt handler should start fetching new
                        \ content to scroll onto the screen
                        \
                        \ See the documentation for screenBufferHi for a
                        \ deeper look into the exact values that are set

 RTS                    \ Return from the subroutine