Flight: WARP

       Name: WARP                                                    [Show more]
       Type: Subroutine
   Category: Flight
    Summary: Process the fast-forward button to end the demo, dock instantly or
             perform an in-system jump
  Deep dive: A sense of scale
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Main flight loop (Part 3 of 16) calls WARP


 This routine does a similar job to the routine of the same name in the BBC
 Master version of Elite, but the code is significantly different.


.WARP

 LDA demoInProgress     ; If the demo is not in progress, jump to warp1 to skip
 BEQ warp1              ; the following

                        ; If we get here then the demo is in progress, in which
                        ; case the fast-forward icon ends the demo and starts
                        ; the game

 JSR ResetShipStatus    ; Reset the ship's speed, hyperspace counter, laser
                        ; temperature, shields and energy banks

 JMP StartGame          ; Jump to StartGame to reset the stack and go to the
                        ; docking bay (i.e. show the Status Mode screen)

.warp1

 LDA auto               ; If the docking computer is engaged (auto is non-zero)
 AND SSPR               ; and we are inside the space station safe zone (SSPR
 BEQ warp2              ; is non-zero), then this sets A to be non-zero, so if
                        ; this is not the case, jump to warp2 to skip the
                        ; following

                        ; If we get here then the docking computer is engaged
                        ; and we are in the space station safe zone, in which
                        ; case the fast-forward button docks us instantly

 JMP GOIN               ; Go to the docking bay (i.e. show the ship hangar
                        ; screen) and return from the subroutine with a tail
                        ; call

.warp2

 JSR FastForwardJump    ; Do an in-system (fast-forward) jump and run the
                        ; distance checks

 BCS warp3              ; If the C flag is set then we are too close to the
                        ; planet or sun for any more jumps, so jump to warp3
                        ; to stop jumping

 JSR FastForwardJump    ; Do a second in-system (fast-forward) jump and run the
                        ; distance checks

 BCS warp3              ; If the C flag is set then we are too close to the
                        ; planet or sun for any more jumps, so jump to warp3
                        ; to stop jumping

 JSR FastForwardJump    ; Do a third in-system (fast-forward) jump and run the
                        ; distance checks

 BCS warp3              ; If the C flag is set then we are too close to the
                        ; planet or sun for any more jumps, so jump to warp3
                        ; to stop jumping

 JSR WaitForNMI         ; Wait until the next NMI interrupt has passed (i.e. the
                        ; next VBlank)

 JSR InSystemJump       ; Do a fourth in-system jump (fast-forward) without
                        ; doing the distance checks

.warp3

 LDA #1                 ; Set the main loop counter to 1, so the next iteration
 STA MCNT               ; through the main loop will potentially spawn ships
                        ; (see part 2 of the main game loop at me3)

 LSR A                  ; Set EV, the extra vessels spawning counter, to 0
 STA EV                 ; (the LSR produces a 0 as A was previously 1)

 JSR CheckAltitude      ; Perform an altitude check with the planet, ending the
                        ; game if we hit the ground

 LDA QQ11               ; If this is not the space view, jump to warp4 to skip
 BNE warp4              ; the updating of the space view and return from the
                        ; subroutine

 LDX VIEW               ; Set X to the current view (front, rear, left or right)

 DEC VIEW               ; Decrement the view in VIEW so the call to LOOK1 thinks
                        ; the view has changed, so it will update the screen

 JMP LOOK1              ; Jump to LOOK1 to initialise the view in X, returning
                        ; from the subroutine using a tail call

.warp4

 RTS                    ; Return from the subroutine