Track geometry: GetSectionCoords

       Name: GetSectionCoords                                        [Show more]
       Type: Subroutine
   Category: Track geometry
    Summary: Copy two three-part 16-bit coordinates from the track section data
  Deep dive: Building a 3D track from sections and segments
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * GetFirstSegment calls GetSectionCoords


 This routine is normally called with X as a multiple of 3 in the range 0 to
 117, representing track segments 0 to 39. The routine copies the following
 track section coordinates from the track section data for section Y * 8:

   * xTrackSectionI
   * yTrackSectionI
   * zTrackSectionI

 and stores them in the X-th coordinate in (xSegmentCoordI, ySegmentCoordI,
 zSegmentCoordI). It also copies the following track section coordinates:

   * xTrackSectionO
   * yTrackSectionI
   * zTrackSectionO

 and stores them in the X-th coordinate in (xSegmentCoordO, ySegmentCoordO,
 zSegmentCoordO). Note that the y-coordinate is set to the same value as the
 y-coordinate from the first copy.

 It also sets thisVectorNumber to trackSectionFrom for the Y-th track section
 data.

 Specifically, this copies data from the Y-th track section entry:

   (xTrackSectionIHi xTrackSectionILo)
   (yTrackSectionIHi yTrackSectionILo)
   (zTrackSectionIHi zTrackSectionILo)
   (xTrackSectionOHi xTrackSectionOLo)
   (yTrackSectionIHi yTrackSectionILo)
   (zTrackSectionOHi zTrackSectionOLo)
   trackSectionFrom

 and stores it in the X-th track segment:

   (xSegmentCoordIHi xSegmentCoordILo)
   (ySegmentCoordIHi ySegmentCoordILo)
   (zSegmentCoordIHi zSegmentCoordILo)
   (xSegmentCoordOHi xSegmentCoordOLo)
   (ySegmentCoordOHi ySegmentCoordOLo)
   (zSegmentCoordOHi zSegmentCoordOLo)
   thisVectorNumber


 Arguments:

   Y                    The number of the track section * 8 whose coordinates we
                        want to fetch

   X                    The index * 3 of the track segment where we store the
                        coordinates


.GetSectionCoords

 JSR GetSectionCoord    \ Copy the following 16-bit coordinate:
                        \
                        \   * The Y-th xTrackSectionI to the X-th xSegmentCoordI
                        \
                        \   * The Y-th yTrackSectionI to the X-th ySegmentCoordI
                        \
                        \   * The Y-th zTrackSectionI to the X-th zSegmentCoordI

 LDA xTrackSectionOLo,Y \ Copy the following 16-bit coordinate:
 STA xSegmentCoordOLo,X \
 LDA zTrackSectionOLo,Y \   * The Y-th xTrackSectionO to the X-th xSegmentCoordO
 STA zSegmentCoordOLo,X \
                        \   * The Y-th zTrackSectionO to the X-th zSegmentCoordO
                        \
                        \ starting with the low bytes

 LDA xTrackSectionOHi,Y \ And then the high bytes
 STA xSegmentCoordOHi,X
 LDA zTrackSectionOHi,Y
 STA zSegmentCoordOHi,X

 LDA trackSectionFrom,Y \ Set thisVectorNumber = the Y-th trackSectionFrom
 STA thisVectorNumber

                        \ Fall through into CopySectionData to copy the
                        \ following 16-bit coordinate:
                        \
                        \   * The Y-th yTrackSectionI to the X-th ySegmentCoordO
                        \
                        \ This works because the call to GetSectionCoord already
                        \ stored the Y-th yTrackSectionI in the X-th
                        \ ySegmentCoordI, and the following now copies that into
                        \ the X-th ySegmentCoordO