Extra tracks: HookUpdateHorizon

       Name: HookUpdateHorizon                                       [Show more]
       Type: Subroutine
   Category: Extra tracks
    Summary: Only update the horizon if we have found fewer than 12 visible
             segments
  Deep dive: Secrets of 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 HookUpdateHorizon
             * newContentLo calls HookUpdateHorizon


 This routine is called from GetVergeAndMarkers so that we only store
 horizonLine and horizonListIndex when segmentCounter < 12.


.HookUpdateHorizon

 PHA                    \ Store A on the stack so we can retrieve it below

 LDA segmentCounter     \ Set the C flag if segmentCounter >= 12
 CMP #12

 PLA                    \ Retrieve the value of A from the stack

 BCS upho1              \ If segmentCounter >= 12, jump to upho1 to skip the
                        \ following two instructions

                        \ Otherwise we set the horizon line and index using the
                        \ same code that we overwrote with the call to the hook
                        \ routine

 STA horizonLine        \ This track segment is higher than the current horizon
                        \ pitch angle, so the track obscures the horizon and we
                        \ need to update horizonLine to this new pitch angle

 STY horizonListIndex   \ Set horizonListIndex to the track segment number in Y

.upho1

 RTS                    \ Return from the subroutine