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⌂ ∞ ▽ Aviator on the BBC Micro

3D geometry: SetObjectCoords (Part 4 of 11)

       Name: SetObjectCoords (Part 4 of 11)                          [Show more]
       Type: Subroutine
   Category: 3D geometry
    Summary: Pre-process the object groups (objects 6, 7, 8 or 9)
  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 6, 7, 8 or 9, so
                        \ this is an object group (e.g. a tree)

 LDA #8                 \ Set objCount = 8 to act as a counter in the loop
 STA objCount           \ below, so we work through all 8 objects in this object
                        \ group

.objc2

 LDX objectGroup-6,Y    \ Set X = 0, 8, 16 or 24, for Y = 6, 7, 8 or 9
                        \
                        \ (or 1, 9, 17, 25 etc., depending on the current group)

 LDA xGroupObjectHi,X   \ Set the object's x-coordinate to the X-th entry in
 STA xObjectHi,Y        \ xGroupObjectHi, which contains the high byte of the
                        \ group object's x-coordinate

 LDA zGroupObjectHi,X   \ Set the object's z-coordinate to the X-th entry in
 STA zObjectHi,Y        \ zGroupObjectHi, which contains the high byte of the
                        \ group object's z-coordinate

 JMP objc9              \ Jump to objc9 to process this object