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⌂ ∞ ▽ Elite on the BBC Micro and NES

Universe: Ze

[Elite-A, Parasite]

       Name: Ze                                                      [Show more]
       Type: Subroutine
   Category: Universe
    Summary: Initialise the INWK workspace to a hostile ship
  Deep dive: Fixing ship positions

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DEATH calls Ze
             * GTHG calls Ze
             * Main game loop for flight (Part 3 of 6) calls Ze




 Specifically, this routine does the following:

   * Reset the INWK ship workspace

   * Set the ship to a fair distance away in all axes, in front of us but
     randomly up or down, left or right

   * Give the ship a 4% chance of having E.C.M.

   * Set the ship to hostile, with AI enabled

 This routine also sets A, X, T1 and the C flag to random values.

 Note that because this routine uses the value of X returned by DORND, and X
 contains the value of A returned by the previous call to DORND, this routine
 does not necessarily set the new ship to a totally random location. See the
 deep dive on "Fixing ship positions" for details.



.Ze

 JSR rand_posn          \ Call rand_posn to set up the INWK workspace for a ship
                        \ in a random ship position, and set T1 to a random
                        \ number

 CMP #245               \ Set the C flag if A >= 245 (4% chance)

 ROL A                  \ Set bit 0 of A to the C flag (i.e. there's a 4%
                        \ chance of this ship having E.C.M.)

 ORA #%11000000         \ Set bits 6 and 7 of A, so the ship is hostile (bit 6
                        \ and has AI (bit 7)

 STA INWK+32            \ Store A in the AI flag of this ship

                        \ Fall through into DORND2 to set A, X and the C flag
                        \ randomly