Skip to navigation

Elite on the BBC Micro

Version analysis of Main game loop (Part 3 of 6)

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 game loop (Part 3 of 6) Type: Subroutine Category: Main loop Summary: Potentially spawn a cop, particularly if we've been bad Deep dive: Program flow of the main game loop Ship data blocks Fixing ship positions
This section covers the following: * Potentially spawn a cop (in a Viper), very rarely if we have been good, more often if have been naughty, and very often if we have been properly bad

Code variation 1 of 4A variation in the comments only

This variation is blank in the Cassette, Disc (flight) and Electron versions.

6502SP, Master

* Very rarely, consider spawning a Thargoid, or vanishingly rarely, a Cougar
.MTT1

Code variation 2 of 4Minor and very low-impact

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

Cassette, Electron

Flight, 6502SP, Master

LDA SSPR \ If we are inside the space station's safe zone, jump BNE MLOOP \ to MLOOP to skip the following
LDA SSPR \ If we are outside the space station's safe zone, skip BEQ P%+5 \ the following instruction .MLOOPS JMP MLOOP \ Jump to MLOOP to skip the following
 JSR BAD                \ Call BAD to work out how much illegal contraband we
                        \ are carrying in our hold (A is up to 40 for a
                        \ standard hold crammed with contraband, up to 70 for
                        \ an extended cargo hold full of narcotics and slaves)

 ASL A                  \ Double A to a maximum of 80 or 140

 LDX MANY+COPS          \ If there are no cops in the local bubble, skip the
 BEQ P%+5               \ next instruction

 ORA FIST               \ There are cops in the vicinity and we've got a hold
                        \ full of jail time, so OR the value in A with FIST to
                        \ get a new value that is at least as high as both
                        \ values, to reflect the fact that they have almost
                        \ certainly scanned our ship

 STA T                  \ Store our badness level in T

 JSR Ze                 \ Call Ze to initialise INWK to a potentially hostile
                        \ ship, and set A and X to random values
                        \
                        \ Note that because Ze uses the value of X returned by
                        \ DORND, and X contains the value of A returned by the
                        \ previous call to DORND, this does not set the new ship
                        \ to a totally random location. See the deep dive on
                        \ "Fixing ship positions" for details

Code variation 3 of 4Related to an advanced feature

When considering spawning cops, the advanced versions have a 0.4% chance of spawning a Cougar or a Thargoid instead.

This variation is blank in the Cassette, Disc (flight) and Electron versions.

6502SP, Master

CMP #136 \ If the random number in A = 136 (0.4% chance), jump BEQ fothg \ to fothg in part 4 to spawn either a Thargoid or, very \ rarely, a Cougar
 CMP T                  \ If the random value in A >= our badness level, which
 BCS P%+7               \ will be the case unless we have been really, really
                        \ bad, then skip the following two instructions (so
                        \ if we are really bad, there's a higher chance of
                        \ spawning a cop, otherwise we got away with it, for
                        \ now)

 LDA #COPS              \ Add a new police ship to the local bubble
 JSR NWSHP

Code variation 4 of 4A 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

LDA MANY+COPS \ If we now have at least one cop in the local bubble, BNE MLOOP \ jump down to MLOOP, otherwise fall through into the \ next part to look at spawning something else
LDA MANY+COPS \ If we now have at least one cop in the local bubble, BNE MLOOPS \ jump down to MLOOPS to stop spawning, otherwise fall \ through into the next part to look at spawning \ something else
RSS Feed