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⌂ ∞ Revs on the BBC Micro

Extra tracks: Hook80Percent

       Name: Hook80Percent                                           [Show more]
       Type: Subroutine
   Category: Extra tracks
    Summary: Set the horizonTrackWidth to 80% of the width of the track on the
             horizon
  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 Hook80Percent
             * newContentLo calls Hook80Percent




 This routine is called from GetTrackAndMarkers to set the horizonTrackWidth to
 80% of the width of the track on the horizon.



.Hook80Percent

 STA U                  \ Set U = A

 LDA #205               \ Set A = 205

 JMP Multiply8x8        \ Set (A T) = A * U
                        \           = 205 * A
                        \
                        \ returning from the subroutine using a tail call
                        \
                        \ This calculates the following in A:
                        \
                        \   A = (A T) / 256
                        \     = 205 * A / 256
                        \     = 0.80 * A

 EQUB &00               \ This byte appears to be unused