Extra tracks: HookFieldOfView

       Name: HookFieldOfView                                         [Show more]
       Type: Subroutine
   Category: Extra tracks
    Summary: When populating the verge buffer in GetSegmentAngles, don't give
             up so easily when we get segments outside the field of view
  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 HookFieldOfView
             * newContentLo calls HookFieldOfView


 This routine is called from GetSegmentAngles to change the logic in at label
 gseg12, which is applied when a segment is outside the field of view. Note
 that in the following, the previous segment is further away than the current
 one.

 In the original code:

   * If previous segment's yaw angle >= 20 then the previous segment was also
     outside the field of view, so return from the subroutine.

   * Otherwise go to gseg4 to try reducing the size of the segment before
     returning.

 In the new code:

   * If previous segment's yaw angle >= 20 and segmentCounter >= 10, then the
     previous segment was also outside the field of view AND we have already
     marked at least 10 segments as being visible, so return from the
     subroutine.

   * Otherwise go to gseg13 to mark this segment as visible and keep checking
     segments.

 So in the modified version, we keep checking segments until we have reached at
 least 10.


 Arguments:

   A                    Yaw angle for the previous segment's right verge

   C flag               Set according to CMP #20


.HookFieldOfView

 BCC fovw1              \ If A < 20, then this segment is within the 20-degree
                        \ field of view, jump to gseg13 via fovw1

 LDA segmentCounter     \ If segmentCounter < 10, jump to gseg13 via fovw1
 CMP #10
 BCC fovw1

 RTS                    \ Return from the subroutine

.fovw1

 JMP gseg13             \ Jump to gseg13