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BBC Micro Elite

Main loop: Main flight loop (Part 11 of 16) (Disc version)

Name: Main flight loop (Part 11 of 16) [View in context] Type: Subroutine Category: Main loop Summary: For each nearby ship: Process missile lock and firing our laser Deep dive: Program flow of the main game loop Flipping axes between space views
The main flight loop covers most of the flight-specific aspects of Elite. This section covers the following: * Continue looping through all the ships in the local bubble, and for each one: * If this is not the front space view, flip the axes of the ship's coordinates in INWK * Process missile lock * Process our laser firing
.MA26 LDA NEWB \ If bit 7 of the ship's NEWB flags is clear, skip the BPL P%+5 \ following instruction JSR SCAN \ Bit 7 of the ship's NEWB flags is set, which means the \ ship has docked or been scooped, so we draw the ship \ on the scanner, which has the effect of removing it LDA QQ11 \ If this is not a space view, jump to MA15 to skip BNE MA15 \ missile and laser locking LDX VIEW \ Load the current view into X BEQ P%+5 \ If the current view is the front view, skip the \ following instruction, as the geometry in INWK is \ already correct JSR PU1 \ Call PU1 to update the geometric axes in INWK to \ match the view (front, rear, left, right) JSR HITCH \ Call HITCH to see if this ship is in the crosshairs, BCC MA8 \ in which case the C flag will be set (so if there is \ no missile or laser lock, we jump to MA8 to skip the \ following) LDA MSAR \ We have missile lock, so check whether the leftmost BEQ MA47 \ missile is currently armed, and if not, jump to MA47 \ to process laser fire, as we can't lock an unarmed \ missile JSR BEEP \ We have missile lock and an armed missile, so call \ the BEEP subroutine to make a short, high beep LDX XSAV \ Call ABORT2 to store the details of this missile LDY #&0E \ lock, with the targeted ship's slot number in X JSR ABORT2 \ (which we stored in XSAV at the start of this ship's \ loop at MAL1), and set the colour of the missile \ indicator to the colour in Y (red = &0E) .MA47 \ If we get here then the ship is in our sights, but \ we didn't lock a missile, so let's see if we're \ firing the laser LDA LAS \ If we are firing the laser then LAS will contain the BEQ MA8 \ laser power (which we set in MA68 above), so if this \ is zero, jump down to MA8 to skip the following LDX #15 \ We are firing our laser and the ship in INWK is in JSR EXNO \ the crosshairs, so call EXNO to make the sound of \ us making a laser strike on another ship LDA TYPE \ Did we just hit the space station? If so, jump to CMP #SST \ MA14+2 to make the station hostile, skipping the BEQ MA14+2 \ following as we can't destroy a space station CMP #CON \ If the ship we hit is not a Constrictor, jump tp BURN BNE BURN \ to skip the following LDA LAS \ Set A to the power of the laser we just used to hit \ the ship (i.e. the laser in the current view) CMP #(Armlas AND 127) \ If the laser is not a military laser, jump to MA8 BNE MA8 \ to skip the following, as only military lasers have \ any effect on the Constrictor LSR LAS \ Divide the laser power of the current view by 4, so LSR LAS \ the damage inflicted on the super-ship is a quarter of \ the damage our military lasers would inflict on a \ normal ship .BURN LDA INWK+35 \ Fetch the hit ship's energy from byte #35 and subtract SEC \ our current laser power, and if the result is greater SBC LAS \ than zero, the other ship has survived the hit, so BCS MA14 \ jump down to MA14 ASL INWK+31 \ Set bit 7 of the ship byte #31 to indicate that it has SEC \ now been killed ROR INWK+31 LDA TYPE \ Did we just kill an asteroid? If not, jump to nosp, CMP #AST \ otherwise keep going BNE nosp LDA LAS \ Did we kill the asteroid using mining lasers? If not, CMP #Mlas \ jump to nosp, otherwise keep going BNE nosp JSR DORND \ Set A and X to random numbers LDX #SPL \ Set X to the ship type for a splinter AND #3 \ Reduce the random number in A to the range 0-3 JSR SPIN2 \ Call SPIN2 to spawn A items of type X (i.e. spawn \ 0-3 spliters) .nosp LDY #PLT \ Randomly spawn some alloy plates JSR SPIN LDY #OIL \ Randomly spawn some cargo canisters JSR SPIN JSR EXNO2 \ Call EXNO2 to process the fact that we have killed a \ ship (so increase the kill tally, make an explosion \ sound and so on) .MA14 STA INWK+35 \ Store the hit ship's updated energy in ship byte #35 LDA TYPE \ Call ANGRY to make this ship hostile, now that we JSR ANGRY \ have hit it