Flight: TT18

       Name: TT18                                                    [Show more]
       Type: Subroutine
   Category: Flight
    Summary: Try to initiate a jump into hyperspace
    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * TT102 calls TT18


 Try to go through hyperspace. Called from TT102 in the main loop when the
 hyperspace countdown has finished.


.TT18

IF _SNG45 OR _SOURCE_DISC

 LDA QQ14               \ Subtract the distance to the selected system (in QQ8)
 SEC                    \ from the amount of fuel in our tank (in QQ14) into A
 SBC QQ8

ELIF _EXECUTIVE

 LDA QQ14               \ Subtract the distance to the selected system (in QQ8)

 BIT JUMP               \ If infinite jump range is configured, then jump down
 BMI IJUMP              \ to IJUMP so we don't subtract any fuel for this jump

 SEC                    \ from the amount of fuel in our tank (in QQ14) into A
 SBC QQ8

ENDIF

 BCS P%+4               \ If the subtraction didn't overflow, skip the next
                        \ instruction

 LDA #0                 \ The subtraction overflowed, so set A = 0 so we don't
                        \ end up with a negative amount of fuel

 STA QQ14               \ Store the updated fuel amount in QQ14

IF _EXECUTIVE

.IJUMP

ENDIF

 LDA QQ11               \ If the current view is not a space view, jump to ee5
 BNE ee5                \ to skip the following

 JSR TT66               \ Clear the top part of the screen, draw a white border,
                        \ and set the current view type in QQ11 to 0 (space
                        \ view)

 JSR LL164              \ Call LL164 to show the hyperspace tunnel and make the
                        \ hyperspace sound

.ee5

 JSR CTRL               \ Scan the keyboard to see if CTRL is currently pressed,
                        \ returning a negative value in A if it is

 AND PATG               \ If the game is configured to show the author's names
                        \ on the start-up screen, then PATG will contain &FF,
                        \ otherwise it will be 0

 BMI ptg                \ By now, A will be negative if we are holding down CTRL
                        \ and author names are configured, which is what we have
                        \ to do in order to trigger a manual mis-jump, so jump
                        \ to ptg to do a mis-jump (ptg not only mis-jumps, but
                        \ updates the competition flags, so Acornsoft could tell
                        \ from the competition code whether this feature had
                        \ been used)

 JSR DORND              \ Set A and X to random numbers

 CMP #253               \ If A >= 253 (0.78% chance) then jump to MJP to trigger
 BCS MJP                \ a mis-jump into witchspace

\JSR TT111              \ This instruction is commented out in the original
                        \ source. It finds the closest system to coordinates
                        \ (QQ9, QQ10), but we don't need to do this as the
                        \ crosshairs will already be on a system by this point

 JSR hyp1+3             \ Jump straight to the system at (QQ9, QQ10) without
                        \ first calculating which system is closest

 JSR RES2               \ Reset a number of flight variables and workspaces

 JSR SOLAR              \ Halve our legal status, update the missile indicators,
                        \ and set up data blocks and slots for the planet and
                        \ sun

\JSR CATLOD             \ These instructions are commented out in the original
\JSR LOMOD              \ source

 LDA QQ11               \ If the current view in QQ11 is not a space view (0) or
 AND #%00111111         \ one of the charts (64 or 128), return from the
 BNE RTS111             \ subroutine (as RTS111 contains an RTS)

 JSR TTX66              \ Otherwise clear the screen and draw a white border

 LDA QQ11               \ If the current view is one of the charts, jump to
 BNE TT114              \ TT114 (from which we jump to the correct routine to
                        \ display the chart)

 INC QQ11               \ This is a space view, so increment QQ11 to 1

                        \ Fall through into TT110 to show the front space view