Skip to navigation

Elite on the BBC Micro

Version analysis of Main flight loop (Part 12 of 16)

This code appears in the following versions (click to see it in the source code):

Code variations between these versions are shown below.

Name: Main flight loop (Part 12 of 16) Type: Subroutine Category: Main loop Summary: For each nearby ship: Draw the ship, remove if killed, loop back Deep dive: Program flow of the main game loop Drawing ships
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: * Draw the ship * Process removal of killed ships * Loop back up to MAL1 to move onto the next ship in the local bubble
.MA8 JSR LL9 \ Call LL9 to draw the ship we're processing on-screen .MA15 LDY #35 \ Fetch the ship's energy from byte #35 and copy it to LDA INWK+35 \ byte #35 in INF (so the ship's data in K% gets STA (INF),Y \ updated)

Code variation 1 of 6Related to an enhanced feature

Ships that have docked or been scooped in the enhanced versions are not classed as being killed and are not tested for potential bounties.

This variation is blank in the Cassette and Electron versions.

Flight, 6502SP, Master

LDA NEWB \ If bit 7 of the ship's NEWB flags is set, which means BMI KS1S \ the ship has docked or been scooped, jump to KS1S to \ skip the following, as we can't get a bounty for a \ ship that's no longer around
 LDA INWK+31            \ If bit 7 of the ship's byte #31 is clear, then the
 BPL MAC1               \ ship hasn't been killed by energy bomb, collision or
                        \ laser fire, so jump to MAC1 to skip the following

Code variation 2 of 6A variation in the labels only

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Electron

Flight, 6502SP, Master

AND #%00100000 \ If bit 5 of the ship's byte #31 is clear then the BEQ NBOUN \ ship is no longer exploding, so jump to NBOUN to skip \ the following
AND #%00100000 \ If bit 5 of the ship's byte #31 is clear then the BEQ MAC1 \ ship is no longer exploding, so jump to MAC1 to skip \ the following

Code variation 3 of 6Specific to an individual platform

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Electron

Flight, 6502SP, Master

LDA TYPE \ If the ship we just destroyed was a cop, keep going, CMP #COPS \ otherwise jump to q2 to skip the following BNE q2 LDA FIST \ We shot the sheriff, so update our FIST flag ORA #64 \ ("fugitive/innocent status") to at least 64, which STA FIST \ will instantly make us a fugitive .q2
LDA NEWB \ Extract bit 6 of the ship's NEWB flags, so A = 64 if AND #%01000000 \ bit 6 is set, or 0 if it is clear. Bit 6 is set if \ this ship is a cop, so A = 64 if we just killed a \ policeman, otherwise it is 0 ORA FIST \ Update our FIST flag ("fugitive/innocent status") to STA FIST \ at least the value in A, which will instantly make us \ a fugitive if we just shot the sheriff, but won't \ affect our status if the enemy wasn't a copper

Code variation 4 of 6Related to a standard feature

This is a bug in all versions. Making a kill while there's an in-flight message on the screen not only stops the bounty from being displayed (which is intentional), but it also prevents the bounty from being awarded (which presumably isn't). In non-Electron versions, the same code is used to prevent bounties from being awarded in witchspace (which is correct, as witchspace kills can't be reported to the authorities).

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, 6502SP, Master

Electron

LDA DLY \ If we already have an in-flight message on-screen (in ORA MJ \ which case DLY > 0), or we are in witchspace (in BNE KS1S \ which case MJ > 0), jump to KS1S to skip showing an \ on-screen bounty for this kill
LDA DLY \ If we already have an in-flight message on-screen (in BNE KS1S \ which case DLY > 0), jump to KS1S to skip showing an \ on-screen bounty for this kill
 LDY #10                \ Fetch byte #10 of the ship's blueprint, which is the
 LDA (XX0),Y            \ low byte of the bounty awarded when this ship is
 BEQ KS1S               \ killed (in Cr * 10), and if it's zero jump to KS1S as
                        \ there is no on-screen bounty to display

 TAX                    \ Put the low byte of the bounty into X

 INY                    \ Fetch byte #11 of the ship's blueprint, which is the
 LDA (XX0),Y            \ high byte of the bounty awarded (in Cr * 10), and put
 TAY                    \ it into Y

 JSR MCASH              \ Call MCASH to add (Y X) to the cash pot

 LDA #0                 \ Print control code 0 (current cash, right-aligned to
 JSR MESS               \ width 9, then " CR", newline) as an in-flight message

.KS1S

 JMP KS1                \ Process the killing of this ship (which removes this
                        \ ship from its slot and shuffles all the other ships
                        \ down to close up the gap)

Code variation 5 of 6A variation in the labels only

This variation is blank in the Disc (flight), 6502 Second Processor and Master versions.

Cassette, Electron

.NBOUN
.MAC1

Code variation 6 of 6A variation in the comments only

Tap on a version to expand it, and tap it again to show to all variations.

Cassette, Flight, 6502SP, Master

Electron

LDA TYPE \ If the ship we are processing is a planet or sun, BMI MA27 \ jump to MA27 to skip the following two instructions
LDA TYPE \ If the ship we are processing is the planet, jump to BMI MA27 \ MA27 to skip the following two instructions
 JSR FAROF              \ If the ship we are processing is a long way away (its
 BCC KS1S               \ distance in any one direction is > 224, jump to KS1S
                        \ to remove the ship from our local bubble, as it's just
                        \ left the building

.MA27

 LDY #31                \ Fetch the ship's explosion/killed state from byte #31
 LDA INWK+31            \ and copy it to byte #31 in INF (so the ship's data in
 STA (INF),Y            \ K% gets updated)

 LDX XSAV               \ We're done processing this ship, so fetch the ship's
                        \ slot number, which we saved in XSAV back at the start
                        \ of the loop

 INX                    \ Increment the slot number to move on to the next slot

 JMP MAL1               \ And jump back up to the beginning of the loop to get
                        \ the next ship in the local bubble for processing

RSS Feed