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Main loop: Main flight loop (Part 16 of 16)

[BBC Micro cassette version]

Name: Main flight loop (Part 16 of 16) [Show more] Type: Subroutine Category: Main loop Summary: Process laser pulsing, E.C.M. energy drain, call stardust routine Deep dive: Program flow of the main game loop
Context: See this subroutine in context in the source code Variations: See code variations for this subroutine in the different versions References: No direct references to this subroutine in this source file

The main flight loop covers most of the flight-specific aspects of Elite. This section covers the following: * Process laser pulsing * Process E.C.M. energy drain * Jump to the stardust routine if we are in a space view * Return from the main flight loop
.MA23 LDA LAS2 \ If the current view has no laser, jump to MA16 to skip BEQ MA16 \ the following LDA LASCT \ If LASCT >= 8, jump to MA16 to skip the following, so CMP #8 \ for a pulse laser with a LASCT between 8 and 10, the BCS MA16 \ laser stays on, but for a LASCT of 7 or less it gets \ turned off and stays off until LASCT reaches zero and \ the next pulse can start (if the fire button is still \ being pressed) \ \ For pulse lasers, LASCT gets set to 10 in ma1 above, \ and it decrements every vertical sync (50 times a \ second), so this means it pulses five times a second, \ with the laser being on for the first 3/10 of each \ pulse and off for the rest of the pulse \ \ If this is a beam laser, LASCT is 0 so we always keep \ going here. This means the laser doesn't pulse, but it \ does get drawn and removed every cycle, in a slightly \ different place each time, so the beams still flicker \ around the screen JSR LASLI2 \ Redraw the existing laser lines, which has the effect \ of removing them from the screen LDA #0 \ Set LAS2 to 0 so if this is a pulse laser, it will STA LAS2 \ skip over the above until the next pulse (this has no \ effect if this is a beam laser) .MA16 LDA ECMP \ If our E.C.M is not on, skip to MA69, otherwise keep BEQ MA69 \ going to drain some energy JSR DENGY \ Call DENGY to deplete our energy banks by 1 BEQ MA70 \ If we have no energy left, jump to MA70 to turn our \ E.C.M. off .MA69 LDA ECMA \ If an E.C.M is going off (ours or an opponent's) then BEQ MA66 \ keep going, otherwise skip to MA66 DEC ECMA \ Decrement the E.C.M. countdown timer, and if it has BNE MA66 \ reached zero, keep going, otherwise skip to MA66 .MA70 JSR ECMOF \ If we get here then either we have either run out of \ energy, or the E.C.M. timer has run down, so switch \ off the E.C.M. .MA66 LDA QQ11 \ If this is not a space view (i.e. QQ11 is non-zero) BNE MA9 \ then jump to MA9 to return from the main flight loop \ (as MA9 is an RTS) JMP STARS \ This is a space view, so jump to the STARS routine to \ process the stardust, and return from the main flight \ loop using a tail call