Extra tracks: HookDataPointers

       Name: HookDataPointers                                        [Show more]
       Type: Subroutine
   Category: Extra tracks
    Summary: If the current section is dynamically generated, update the data
             pointers
  Deep dive: Secrets of the extra tracks
             Dynamic track generation in the extra tracks
             Code hooks in the extra tracks
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * newContentHi calls HookDataPointers
             * newContentLo calls HookDataPointers


 This routine is called from part 1 of GetTrackSegment so we update the
 sub-section and sub-section segment pointers when fetching a new track
 segment.

 If bit 6 of the current section's flags is set, then the track segment vectors
 for this section need to be generated from the curve tables (as opposed to
 being calculated as a straight section). When this is the case, this routine
 calls UpdateDataPointers to update the pointers to the next sub-section and
 segment along the track.


.HookDataPointers

 LDA thisSectionFlags   \ If bit 6 of the current section's flags is clear, jump
 AND #%01000000         \ to flab1 to skip the following call, so we just
 BEQ flab1              \ implement the same code as in the original

 JSR UpdateDataPointers \ Bit 6 of the current section's flags is set, so we are
                        \ generating this section's segment vectors using the
                        \ curve tables, so call UpdateDataPointers to update
                        \ the pointers to the next sub-section and segment along
                        \ the track, before continuing with the same code as in
                        \ the original

.flab1

 LDA frontSegmentIndex  \ Set A to the index * 3 of the front track segment in
                        \ the track segment buffer

 CLC                    \ Set A = frontSegmentIndex + 3
 ADC #3                 \
                        \ to move on to the next track segment ahead of the
                        \ current front segment in the track segment buffer,
                        \ which will become the new front segment

 RTS                    \ Return from the subroutine