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⌂ ∞ Elite on the BBC Micro and NES

Icon bar: TT102

[NES version, Bank 0]

       Name: TT102                                                   [Show more]
       Type: Subroutine
   Category: Icon bar
    Summary: Process icon bar controller choices

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Main game loop (Part 6 of 6) calls TT102
             * HME2 calls via ReturnFromSearch




 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.



 Arguments:

   A                    The button number of the chosen icon from the icon bar

   X                    The amount to move the crosshairs in the x-axis

   Y                    The amount to move the crosshairs in the y-axis



 Other entry points:

   ReturnFromSearch     Re-entry point following a system search in HME2



.TT102

 CMP #0                 ; If no icon was chosen, jump to HME1 to skip all the
 BNE P%+5               ; icon checks below
 JMP HME1

 CMP #3                 ; If the Status Mode icon was chosen, jump to STATUS to
 BNE P%+5               ; show the Status Mode screen, returning from the
 JMP STATUS             ; subroutine using a tail call

 CMP #4                 ; If the Charts icon was chosen from the docked icon
 BEQ barb1              ; bar, jump to barb1 to show the correct chart

 CMP #36                ; If the Switch chart range icon from the Charts icon
 BNE barb2              ; bar was not chosen, jump to barb2 to keep checking

 LDA chartToShow        ; The Switch chart range icon from the Charts icon bar
 EOR #%10000000         ; was chosen, so flip bit 7 of chartToShow to toggle
 STA chartToShow        ; the chart between the Long-range and Short-range
                        ; Chart

.barb1

 LDA chartToShow        ; If chartToShow = 0 then jump to TT23 to show the
 BPL P%+5               ; Short-range Chart, otherwise jump to TT22 to show the
 JMP TT22               ; Long-range Chart, in either case returning from the
 JMP TT23               ; subroutine using a tail call

.barb2

 CMP #35                ; If the Data on System icon was chosen, call the
 BNE TT92               ; SetSelectedSystem routine to set the selected system
 JSR SetSelectedSystem  ; to the nearest system, if we don't already have a
 JMP TT25               ; selected system, and then jump to TT25 to show the
                        ; Data on System screen, returning from the subroutine
                        ; using a tail call

.TT92

 CMP #8                 ; If the Inventory icon was chosen, jump to TT213 to
 BNE P%+5               ; show the Inventory screen, returning from the
 JMP TT213              ; subroutine using a tail call

 CMP #2                 ; If the Market Price icon was chosen, jump to TT167 to
 BNE P%+5               ; show the Market Price screen, returning from the
 JMP TT167              ; subroutine using a tail call

 CMP #1                 ; If the Launch icon was not chosen, jump to fvw to
 BNE fvw                ; skip the following launch code

                        ; The Launch icon was chosen, so we now attempt to
                        ; launch

 LDX QQ12               ; If QQ12 is zero then we are not docked, so jump to fvw
 BEQ fvw                ; as we can't launch from the station if we are already
                        ; in space

 JSR SelectNearbySystem ; Set the current system to the nearest system to
                        ; (QQ9, QQ10), which will be the system we are currently
                        ; docked at, and update the selected system flags
                        ; accordingly

 JMP TT110              ; Jump to TT110 to launch our ship, returning from the
                        ; subroutine using a tail call

.fvw

 CMP #17                ; If the Docking Computer icon was not chosen, jump to
 BNE barb8              ; barb8 to move on to the next icon

                        ; If we get here then the Docking Computer icon was
                        ; chosen

 LDX QQ12               ; If QQ12 is non-zero then we are docked, so jump to
 BNE barb8              ; barb8 to move on to the next icon as we can't engage
                        ; the docking computer if we aren't in space

 LDA auto               ; If the docking computer is already activated, jump
 BNE barb5              ; to barb5 to skip the docking fee calculations and
                        ; disable the docking computer (so the icon bar button
                        ; toggles it on and off)

 LDA SSPR               ; If we are not inside the space station safe zone, jump
 BEQ barb8              ; to barb8 to move on to the next icon as we can't
                        ; engage the docking computer if we aren't in the safe
                        ; zone

                        ; We now deduct a docking fee of 5.0 credits for using
                        ; the docking computer

 LDA DKCMP              ; If we have a docking computer fitted (DKCMP is
 ORA chargeDockingFee   ; non-zero) or we have already been charged a docking
 BNE barb4              ; fee (chargeDockingFee is non-zero), then jump to
                        ; barb4 to engage the docking computer without charging
                        ; a docking fee

                        ; Otherwise we do not have a docking computer fitted
                        ; or we have not yet been charged a docking fee, so
                        ; now we charge the docking fee

 LDY #0                 ; Set (Y X) = 50, so the docking fee is 5.0 credits
 LDX #50

 JSR LCASH              ; Subtract (Y X) cash from the cash pot, but only if
                        ; we have enough cash

 BCS barb3              ; If the C flag is set then we did have enough cash for
                        ; the transaction, so jump to barb3 to skip the
                        ; following instruction

                        ; If we get here then we don't have enough cash for the
                        ; docking fee, so make a beep and return from the
                        ; subroutine without engaging the docking computer

 JMP BOOP               ; Call the BOOP routine to make a long, low beep, and
                        ; return from the subroutine using a tail call

.barb3

 DEC chargeDockingFee   ; Set chargeDockingFee to $FF so we don't charge another
                        ; docking fee

 LDA #0                 ; Print control code 0 (current amount of cash and
 JSR MESS               ; newline) as an in-flight message, to show our balance
                        ; after the docking fee has been paid

.barb4

 LDA #1                 ; Set A = 1 to pass to the ChooseMusic routine to play
                        ; the docking music (The Blue Danube)

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

 JSR ChooseMusic_b6     ; Select and play the docking music (tune 1, "The Blue
                        ; Danube")

 LDA #$FF               ; Set A = $FF to set as the value of auto below, so the
                        ; docking computer is flagged as being enabled

 BNE barb6              ; Jump to barb6 to store A in auto (this BNE is
                        ; effectively a JMP as A is never zero)

.barb5

                        ; If we get here then we need to turn off the docking
                        ; computer

 JSR ResetMusicAfterNMI ; Wait for the next NMI before resetting the current
                        ; tune to 0 (no tune) and stopping the docking music

 LDA #0                 ; Set A = 0 to set as the value of auto below, so the
                        ; docking computer is flagged as being disabled

.barb6

 STA auto               ; Set auto to the value in A, to disable or enable the
                        ; docking computer as required

 LDA QQ11               ; If this is the space view, jump to barb7 to return
 BEQ barb7              ; from the subroutine

 JSR CLYNS              ; Clear the bottom two text rows of the upper screen,
                        ; and move the text cursor to column 1 on row 21, i.e.
                        ; the start of the top row of the two bottom rows

 JSR DrawScreenInNMI    ; Configure the NMI handler to draw the screen, so the
                        ; screen gets updated

.barb7

 RTS                    ; Return from the subroutine

.barb8

 JSR CheckForPause      ; If the Start button has been pressed then process the
                        ; pause menu and set the C flag, otherwise clear it

 CMP #21                ; If the "Front space view" icon was not chosen, jump to
 BNE barb11             ; barb11 to move on to the next icon

                        ; If we get here then the "Front space view" icon was
                        ; chosen

 LDA QQ12               ; If QQ12 is zero then we are not docked and in space,
 BPL barb9              ; so jump to barb9 to process the "Front space view"
                        ; icon

 RTS                    ; Otherwise the icon does nothing, so return from the
                        ; subroutine

.barb9

                        ; If we get here then the "Front space view" icon was
                        ; chosen and we are in space

 LDA #0                 ; Set A = 0 to use as the view number if we jump to
                        ; barb10 to show the front space view (i.e. view 0)

 LDX QQ11               ; If this is not the space view, jump to barb10 to show
 BNE barb10             ; the front space view

 LDA VIEW               ; Otherwise add 1 to the view number in VIEW and wrap it
 CLC                    ; round using mod 4, so VIEW goes from 0 to 3 and back
 ADC #1                 ; to 0 again (i.e. front, rear, left, right and back to
 AND #3                 ; front again)

.barb10

 TAX                    ; Set X to the view number to show

 JMP LOOK1              ; Jump to LOOK1 to switch to view X (front, rear, left
                        ; or right), returning from the subroutine using a tail
                        ; call

.barb11

 BIT QQ12               ; If bit 7 of QQ12 is clear (i.e. we are not docked, but
 BPL LABEL_3            ; in space), jump to LABEL_3 to skip the following
                        ; checks for the save commander file key press

 CMP #5                 ; If the Equip Ship icon was chosen, jump to TT219 to
 BNE P%+5               ; show the Equip Ship screen, returning from the
 JMP EQSHP              ; subroutine using a tail call

 CMP #6                 ; If the Save and Load icon was chosen, jump to SVE to
 BNE LABEL_3            ; show the Save and Load screen, returning from the
 JMP SVE_b6             ; subroutine using a tail call

.LABEL_3

 CMP #22                ; If the Hyperspace icon was chosen, jump to hyp to do
 BNE P%+5               ; a hyperspace jump (if we are in space), returning from
 JMP hyp                ; the subroutine using a tail call

 CMP #41                ; If the Galactic Hyperspace icon was chosen, jump to
 BNE P%+5               ; GalacticHyperdrive to do a galactic hyperspace jump,
 JMP GalacticHyperdrive ; returning from the subroutine using a tail call

 CMP #39                ; If the "Search for system" icon was not chosen, jump
 BNE HME1               ; to HME1 to move on to the next icon

 LDA QQ22+1             ; Fetch QQ22+1, which contains the number that's shown
                        ; on-screen during hyperspace countdown

 BNE t95                ; If it is non-zero, return from the subroutine (as t95
                        ; contains an RTS), as there is a countdown in progress

 LDA QQ11               ; If the view in QQ11 is not %0000110x (i.e. 12 or 13,
 AND #%00001110         ; which are the Short-range Chart and Long-range Chart),
 CMP #%00001100         ; jump to t95 to return from the subroutine (as t95
 BNE t95                ; contains an RTS)

 JMP HME2               ; Jump to HME2 to let us search for a system, returning
                        ; from the subroutine using a tail call

.HME1

 STA T1                 ; Store A (the key that's been pressed) in T1

 LDA QQ11               ; If the view in QQ11 is not %0000110x (i.e. 12 or 13,
 AND #%00001110         ; which are the Short-range Chart and Long-range Chart),
 CMP #%00001100         ; jump to TT107 to skip the following and move on to
 BNE TT107              ; updating the hyperspace

 LDA QQ22+1             ; If the on-screen hyperspace counter is non-zero,
 BNE TT107              ; then we are already counting down, so jump to TT107
                        ; to skip the following

 LDA T1                 ; Restore the original value of A (the key that's been
                        ; pressed) from T1

 CMP #38                ; If the "Return pointer to current system" icon was not
 BNE ee2                ; chosen, jump to ee2 to skip the following

 JSR ping               ; Set the target system to the current system (which
                        ; will move the location in (QQ9, QQ10) to the current
                        ; home system

.ReturnFromSearch

 ASL selectedSystemFlag ; Clear bit 7 of selectedSystemFlag to indicate that
 LSR selectedSystemFlag ; there is no currently selected system, so the call to
                        ; SetSelectedSystem selects the system in (QQ9, QQ10)

 JMP SetSelectedSystem  ; Jump to SetSelectedSystem to update the message on
                        ; the chart that shows the current system, returning
                        ; from the subroutine using a tail call

.ee2

 JSR TT16               ; Call TT16 to move the crosshairs by the amount in X
                        ; and Y, which were passed to this subroutine as
                        ; arguments

.TT107

 LDA QQ22+1             ; If the on-screen hyperspace counter is zero, return
 BEQ t95                ; from the subroutine (as t95 contains an RTS), as we
                        ; are not currently counting down to a hyperspace jump

 DEC QQ22               ; Decrement the internal hyperspace counter

 BNE t95                ; If the internal hyperspace counter is still non-zero,
                        ; then we are still counting down, so return from the
                        ; subroutine (as t95 contains an RTS)

                        ; If we get here then the internal hyperspace counter
                        ; has just reached zero and it wasn't zero before, so
                        ; we need to reduce the on-screen counter and update
                        ; the screen. We do this by first printing the next
                        ; number in the countdown sequence, and then printing
                        ; the old number, which will erase the old number
                        ; and display the new one because printing uses EOR
                        ; logic

 LDA #5                 ; Reset the internal hyperspace counter to 5
 STA QQ22

 DEC QQ22+1             ; Decrement the on-screen hyperspace countdown

 BEQ barb12             ; If the countdown is zero, jump to barb12 to do the
                        ; jump

 LDA #250               ; Print in-flight token 250, which is the hyperspace
 JMP MESS               ; countdown, and return from the subroutine using a
                        ; tail call

.barb12

 JMP TT18               ; The countdown has finished, so jump to TT18 to do a
                        ; hyperspace jump, returning from the subroutine using
                        ; a tail call

.t95

 RTS                    ; Return from the subroutine