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⌂ ∞ ▽ Elite on the 6502

Flight: LOOK1

[NES version, Bank 0]

       Name: LOOK1                                                   [Show more]
       Type: Subroutine
   Category: Flight
    Summary: Initialise the space view

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * TT102 calls LOOK1
             * TT110 calls LOOK1
             * WARP calls LOOK1




 Initialise the space view, with the direction of view given in X. This clears
 the upper screen and draws the laser crosshairs, if the view in X has lasers
 fitted. It also wipes all the ships from the scanner, so we can recalculate
 ship positions for the new view (they get put back in the main flight loop).



 Arguments:

   X                    The space view to set:

                          * 0 = front
                          * 1 = rear
                          * 2 = left
                          * 3 = right



 Other entry points:

   LO2                  Contains an RTS



.LO2

 RTS                    ; Return from the subroutine

.LQ

 JSR SendSpaceViewToPPU ; Set a new space view, clear the screen, copy the
                        ; nametable buffers and configure the PPU for the new
                        ; view

 JMP NWSTARS            ; Set up a new stardust field and return from the
                        ; subroutine using a tail call

.LOOK1

 LDA #0                 ; Set A = 0, the type number of a space view

 LDY QQ11               ; If the current view is not a space view, jump up to LQ
 BNE LQ                 ; to set up a new space view

 CPX VIEW               ; If the current view is already of type X, jump to LO2
 BEQ LO2                ; to return from the subroutine (as LO2 contains an RTS)

 JSR SetSpaceViewInNMI  ; Change the current space view to X and configure the
                        ; NMI to send both bitplanes to the PPU during VBlank

 JSR FLIP               ; Swap the x- and y-coordinates of all the stardust
                        ; particles and redraw the stardust field

 JMP WaitForNMI         ; Wait until the next NMI interrupt has passed (i.e. the
                        ; next VBlank) and return from the subroutine using a
                        ; tail call