3D geometry: SetObjectCoords (Part 2 of 11)

       Name: SetObjectCoords (Part 2 of 11)                          [Show more]
       Type: Subroutine
   Category: 3D geometry
    Summary: Pre-process the bullets (objects 12, 13, 14 or 15)
  Deep dive: 3D objects
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


                        \ If we get here then the object ID is 12, 13, 14 or 15,
                        \ so this is a bullet object
                        \
                        \ There are two bullet trails, with objects 13 and 15 at
                        \ the head of the trail (i.e. the bullets), and objects
                        \ 12 and 14 at the back of the bullet trail

 LDA #0                 \ Set K = 0, so the CheckObjDistance routine always
 STA K                  \ returns 0, which means the bullet trails never get
                        \ too far away to be hidden

 LDA yObjectHi,Y        \ If the object's y-coordinate is positive, then the
 BPL objc3              \ bullet is above ground, so jump to objc3 to check the
                        \ next range and then process the bullet

 TYA                    \ If bit 0 of the object ID is set, i.e. the object ID
 AND #1                 \ is 13 or 15, jump to objc3 to check the next range
 BNE objc3              \ and then process the bullet (so objects 13 and 15 can
                        \ be below ground while 12 and 14 are above ground, in
                        \ which case the bullets are still in play)

 JMP objc10             \ The object ID is 12 or 14 (the back end of the bullet
                        \ trail) and the object is below ground level, so jump
                        \ to objc10 to tidy up and return from the subroutine,
                        \ as the bullets have hit the ground