Drawing the track: DrawSegmentEdge (Part 7 of 7)

       Name: DrawSegmentEdge (Part 7 of 7)                           [Show more]
       Type: Subroutine
   Category: Drawing the track
    Summary: Save the angles for the next call to DrawSegmentEdge and return
             from the subroutine
  Deep dive: Drawing the track verges
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


 This part gets things ready for the next call to DrawSegmentEdge, when we draw
 the next segment's verge edge, and returns from the subroutine.


.dver28

 LDA vergeOnScreenEdge  \ If bit 7 of vergeOnScreenEdge is set then the edge we
 BMI dver29             \ are drawing is partially off-screen, so jump to dver29
                        \ to skip the following

                        \ If we get here then the edge we are drawing is wholly
                        \ on-screen, so we can store the edge's angles in M and
                        \ N to be picked up in the next call to DrawSegmentEdge

 LDA W                  \ Set M = W, so we pass on 128 + yaw angle * 4
 STA M

 LDA RR                 \ Set N = RR, so we pass on the pitch angle
 STA N

.dver29

 LDX thisYawIndex       \ Set X to the original yaw angle index that we stored
                        \ above, so X is preserved through calls to the routine

 LDY thisPitchIndex     \ Set Y to the original pitch angle index that we stored
                        \ above, so Y is preserved through calls to the routine

 RTS                    \ Return from the subroutine

 EQUB &A5, &53          \ These bytes appear to be unused
 EQUB &F0, &EB
 EQUB &20, &12
 EQUB &2F, &4C
 EQUB &FC, &2C