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⌂ ∞ ▽ Elite on the BBC Micro and NES

Combat demo: SetupDemoShip

[NES version, Bank 0]

       Name: SetupDemoShip                                           [Show more]
       Type: Subroutine
   Category: Combat demo
    Summary: Set up the ship workspace for a new ship in the combat demo
  Deep dive: The NES combat demo

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * PlayDemo calls SetupDemoShip




.SetupDemoShip

 JSR ZINF               ; Call ZINF to reset the INWK ship workspace and set up
                        ; the orientation vectors so the ship is pointing
                        ; towards us, out of the screen

 LDA #96                ; Set byte #14 = nosev_z_hi = 96 = 1
 STA INWK+14            ;
                        ; So the ship is pointing into the screen

 ORA #%10000000         ; Flip the sign of A to represent a -1

 STA INWK+22            ; Set byte #22 = sidev_x_hi = -96 = -1
                        ;
                        ; So the ship doesn't get reflected in the x-axis by the
                        ; flipping of the z-coordinate, but is instead rotated
                        ; around the y-axis to point into the screen

 LDA #%11111110         ; Set the ship's byte #32 (AI flag) to %11111110, so it
 STA INWK+32            ; has no E.C.M., is hostile, highly aggressive and has
                        ; AI enabled

 LDA #32                ; Set the ship's byte #27 (speed) to 32
 STA INWK+27

                        ; We now set the ship's coordinates to (-40, 40, 60) so
                        ; it is to our upper left and in front of us

 LDA #%10000000         ; Set (x_sign x_lo) = -40
 STA INWK+2
 LDA #40
 STA INWK

 LDA #40                ; Set y_lo = 40
 STA INWK+3

 LDA #60                ; Set z_lo = 60
 STA INWK+6

 RTS                    ; Return from the subroutine