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⌂ ∞ ▽ Elite on the 6502

Missions: BRIEF

[Commodore 64 version]

       Name: BRIEF                                                   [Show more]
       Type: Subroutine
   Category: Missions
    Summary: Start mission 1 and show the mission briefing
  Deep dive: The Constrictor mission

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




 This routine does the following:

   * Clear the screen
   * Display "INCOMING MESSAGE" in the middle of the screen
   * Wait for 2 seconds
   * Clear the screen
   * Show the Constrictor rolling and pitching in the middle of the screen
   * Do this for 64 loop iterations
   * Move the ship away from us and up until it's near the top of the screen
   * Show the mission 1 briefing in extended token 10

 The mission briefing ends with a "{display ship, wait for key press}" token,
 which calls the PAUSE routine. This continues to display the rotating ship,
 waiting until a key is pressed, and then removes the ship from the screen.



.BRIEF

 LSR TP                 ; Set bit 0 of TP to indicate that mission 1 is now in
 SEC                    ; progress
 ROL TP

 JSR BRIS               ; Call BRIS to clear the screen, display "INCOMING
                        ; MESSAGE" and wait for 2 seconds

 JSR ZINF               ; Call ZINF to reset the INWK ship workspace

 LDA #CON               ; Set the ship type in TYPE to the Constrictor
 STA TYPE

 JSR NWSHP              ; Add a new Constrictor to the local bubble (in this
                        ; case, the briefing screen)

 LDA #1                 ; Move the text cursor to column 1
 JSR DOXC

 STA INWK+7             ; Set z_hi = 1, the distance at which we show the
                        ; rotating ship

 JSR TT66               ; Clear the top part of the screen, draw a border box,
                        ; and set the current view type in QQ11 to 1

 LDA #64                ; Set the main loop counter to 64, so the ship rotates
 STA MCNT               ; for 64 iterations through MVEIT

.BRL1

 LDX #%01111111         ; Set the ship's roll counter to a positive roll that
 STX INWK+29            ; doesn't dampen (a clockwise roll)

 STX INWK+30            ; Set the ship's pitch counter to a positive pitch that
                        ; doesn't dampen (a diving pitch)

 JSR LL9                ; Draw the ship on screen

 JSR MVEIT              ; Call MVEIT to rotate the ship in space

 DEC MCNT               ; Decrease the counter in MCNT

 BNE BRL1               ; Loop back to keep moving the ship until we have done
                        ; all 64 iterations

.BRL2

 LSR INWK               ; Halve x_lo so the Constrictor moves towards the centre

 INC INWK+6             ; Increment z_lo so the Constrictor moves away from us

 BEQ BR2                ; If z_lo = 0 (i.e. it just went past 255), jump to BR2
                        ; to show the briefing

 INC INWK+6             ; Increment z_lo so the Constrictor moves a bit further
                        ; away from us

 BEQ BR2                ; If z_lo = 0 (i.e. it just went past 255), jump out of
                        ; the loop to BR2 to stop moving the ship up the screen
                        ; and show the briefing

 LDX INWK+3             ; Set X = y_lo + 1
 INX

 CPX #conhieght         ; If X < conhieght then skip the next instruction
 BCC P%+4

 LDX #conhieght         ; X is bigger than conhieght, so set X = conhieght so
                        ; that X has a maximum value of conhieght

 STX INWK+3             ; Set y_lo = X
                        ;          = y_lo + 1
                        ;
                        ; so the ship moves up the screen (as space coordinates
                        ; have the y-axis going up)

 JSR LL9                ; Draw the ship on screen

 JSR MVEIT              ; Call MVEIT to move and rotate the ship in space

 DEC MCNT               ; Decrease the counter in MCNT

 JMP BRL2               ; Loop back to keep moving the ship up the screen and
                        ; away from us

.BR2

 INC INWK+7             ; Increment z_hi, to keep the ship at the same distance
                        ; as we just incremented z_lo past 255

 LDA #10                ; Set A = 10 so the call to BRP prints extended token 10
                        ; (the briefing for mission 1 where we find out all
                        ; about the stolen Constrictor)

 BNE BRPS               ; Jump to BRP via BRPS to print the extended token in A
                        ; and show the Status Mode screen, returning from the
                        ; subroutine using a tail call (this BNE is effectively
                        ; a JMP as A is never zero)