Maths (Geometry): GetVerticalDelta

       Name: GetVerticalDelta                                        [Show more]
       Type: Subroutine
   Category: Maths (Geometry)
    Summary: Calculate the difference in the y-axis between two objects as a
             signed delta
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * GetObjectAngles calls GetVerticalDelta


 This routine calculates the following:

   yDelta(Hi Lo) = y-coordinate of object #Y - y-coordinate of object #X

 So yDelta(Hi Lo) contains the difference (the "delta") in the y-coordinate
 between the two objects, which is the difference in altitude.


 Arguments:

   X                    The number of the first object

   Y                    The number of the second object


.GetVerticalDelta

 LDA yObjectLo,Y        \ Set yDelta(Hi Lo) =   yObject(Hi Lo) for object #Y
 SEC                    \                     - yObject(Hi Lo) for object #X
 SBC yObjectLo,X        \
 STA yDeltaLo           \ starting with the low bytes

 LDA yObjectHi,Y        \ And then the high bytes
 SBC yObjectHi,X
 STA yDeltaHi

 RTS                    \ Return from the subroutine