Car geometry: CheckForContact

       Name: CheckForContact                                         [Show more]
       Type: Subroutine
   Category: Car geometry
    Summary: Check to see if the object is close enough to the player car to
             make contact
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * BuildRoadSign calls CheckForContact
             * GetObjectAngles calls via CheckForContact-2


 Arguments:

   Y                    Contact is made if objectDistanceLo <= Y

   (J I)                max(|x-delta|, |z-delta|)

   (H G)                min(|x-delta|, |z-delta|)

   M                    The smaller yaw angle of the object, where 0 to 255
                        represents 0 to 45 degrees

   objectNumber         The number of the object being checked for contact


 Other entry points:

   CheckForContact-2    Set Y = 37, so we make contact if (L K) <= 37


 LDY #37                \ Set Y = 37, so we make contact if (L K) <= 37

.CheckForContact

 JSR GetObjectDistance  \ Set (L K) to the distance between the object and the
                        \ player's car

 LDA L                  \ Set objectDistanceHi to the high byte of (L K)
 STA objectDistanceHi

 BNE ccon1              \ If objectDistanceHi is non-zero then the objects are
                        \ too far apart for a collision, so jump to ccon1 to
                        \ return from the subroutine

 CPY K                  \ If K > Y, then the objects are too far apart for a
 BCC ccon1              \ collision, this time in terms of the low byte of the
                        \ distance, so jump to ccon1 to return from the
                        \ subroutine

                        \ If we get here then K <= Y, so the objects are close
                        \ enough for a collision

 DEC processContact     \ Decrement processContact so it is non-zero, so we
                        \ check for contact between this car and the player's
                        \ car in the ProcessContact routine

 LDA K                  \ Set (objectDistanceHi objectDistanceLo) = (L K)
 STA objectDistanceLo

 LDA objectNumber       \ Store the number of the other object in
 STA collisionDriver    \ collisionDriver, so we know who's crashing

.ccon1

 RTS                    \ Return from the subroutine