Track geometry: GetSectionCoord

       Name: GetSectionCoord                                         [Show more]
       Type: Subroutine
   Category: Track geometry
    Summary: Copy a three-part 16-bit coordinate 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:
             * BuildRoadSign calls GetSectionCoord
             * GetSectionAngles (Part 3 of 3) calls GetSectionCoord
             * GetSectionCoords calls GetSectionCoord


 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
 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).

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

   (xTrackSectionIHi xTrackSectionILo)
   (yTrackSectionIHi yTrackSectionILo)
   (zTrackSectionIHi zTrackSectionILo)

 and stores it in the X-th track segment:

   (xSegmentCoordIHi xSegmentCoordILo)
   (ySegmentCoordIHi ySegmentCoordILo)
   (zSegmentCoordIHi zSegmentCoordILo)

 This routine is also called with X = &FD, in which case it copies the
 following:

   Y-th (xTrackSectionIHi xTrackSectionILo) to (xCoord2Hi xCoord2Lo)
   Y-th (yTrackSectionIHi yTrackSectionILo) to (yCoord2Hi yCoord2Lo)
   Y-th (zTrackSectionIHi zTrackSectionILo) to (zCoord2Hi zCoord2Lo)


 Arguments:

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

   X                    The place to store the data:

                          * 0-117 = The index * 3 of the track segment where we
                                    store the coordinates

                          * &FD = Copy to (xCoord2, yCoord2, zCoord2)


.GetSectionCoord

 LDA xTrackSectionILo,Y \ Copy the following 16-bit coordinates:
 STA xSegmentCoordILo,X \
 LDA yTrackSectionILo,Y \   * The Y-th xTrackSectionI to the X-th xSegmentCoordI
 STA ySegmentCoordILo,X \
 LDA zTrackSectionILo,Y \   * The Y-th yTrackSectionI to the X-th ySegmentCoordI
 STA zSegmentCoordILo,X \
                        \   * The Y-th zTrackSectionI to the X-th zSegmentCoordI
                        \
                        \ starting with the low bytes

 LDA xTrackSectionIHi,Y \ And then the high bytes
 STA xSegmentCoordIHi,X
 LDA yTrackSectionIHi,Y
 STA ySegmentCoordIHi,X
 LDA zTrackSectionIHi,Y
 STA zSegmentCoordIHi,X

 RTS                    \ Return from the subroutine