Car geometry: ScaleCarInSegment

       Name: ScaleCarInSegment                                       [Show more]
       Type: Subroutine
   Category: Car geometry
    Summary: Work out how far a car is within a segment by scaling the angle
             in which the car is pointing
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * GetCarInSegment calls ScaleCarInSegment


 This routine takes a car's heading within a segment, as follows:

            0
            |   26
            |  /
            | /  _- 46
            |/_-´
            +--------- 64

 and scales it like this:

   When            Calculate               Range of result

   A < 26          A' = 3 * A              0 to 78
   26 <= A < 46    A' = 4 * A + 52         156 to 232
   A >= 46         A' = A + 190            236 to 253


 Arguments:

   A                    A is in the range 0 to 63


 Returns:

   A                    The scaled value of A, shown as A' above


.ScaleCarInSegment

 CMP #26                \ If A < 26, jump to scar2
 BCC scar2

 CMP #46                \ If A < 46, jump to scar1
 BCC scar1

                        \ If we get here then A >= 46

 CLC                    \ Set A = A + 190
 ADC #190

 RTS                    \ Return from the subroutine

.scar1

                        \ If we get here then 26 <= A < 46

 ASL A                  \ Set A = A << 2 + 52
 ASL A                  \       = 4 * A + 52
 CLC
 ADC #52

 RTS                    \ Return from the subroutine

.scar2

                        \ If we get here then A < 26

 STA T                  \ Set T = A

 ASL A                  \ Set A = A << 1 + T
 CLC                    \       = A * 2 + A
 ADC T                  \       = 3 * A
 ASL A

 RTS                    \ Return from the subroutine