.MA8 JSR LL9_FLIGHT \ 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) 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 collision or laser fire, \ so jump to MAC1 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 \ We now update our FIST flag ("fugitive/innocent \ status") by 1 if we didn't kill a cop, or by a large \ amount if we did - specifically, if we killed a cop, \ then the most significant bit in FIST that is \ currently clear will be set, which means we increase \ FIST by the highest multiple of 2 that we can add and \ still fit the result in a byte \ \ Also, at this point, we know that A = %00100000 (as we \ didn't take the BEQ branch) BIT NEWB \ If bit 6 of the ship's NEWB flags is set, then this BVS n_badboy \ ship is a cop, so jump to n_badboy as we just killed a \ policeman BEQ n_goodboy \ The BIT NEWB instruction sets the Z flag according to \ the result of: \ \ A AND NEWB = %00100000 AND NEWB \ \ so this jumps to n_goodboy if bit 5 of NEWB is clear, \ so in other words, if the ship is no longer exploding, \ we don't update FIST LDA #%10000000 \ Set A so that the shift and rotate instructions we're \ about to do set A = %00000001, so we increase our FIST \ status by just 1 .n_badboy \ We get here with two possible values of A: \ \ * A = %00100000 if we just killed a cop \ * A = %10000000 otherwise ASL A \ Shift and rotate A so that we get: ROL A \ \ * A = %10000000 if we just killed a cop \ * A = %00000001 otherwise .n_bitlegal LSR A \ We now shift A to the right and AND it with FIST, BIT FIST \ repeating the process until the single set bit in A BNE n_bitlegal \ matches a clear bit in FIST, so this shifts A right \ so that the set bit matches the highest clear bit in \ FIST (if we just killed a cop), or it sets A to 0 and \ sets the C flag (if we didn't) ADC FIST \ Set A = A + C + FIST, so: \ \ * A = A + 0 + FIST if we just killed a cop \ * A = 0 + 1 + FIST otherwise \ \ so if we just killed a cop, this will effectively set \ the highest clear bit in FIST, otherwise we just add 1 \ to FIST BCS KS1S \ If the addition overflowed, jump to KS1S to skip \ showing an on-screen bounty for this kill, and without \ updating FIST first (as we are too bad to get any \ worse) STA FIST \ Otherwise update the value of FIST to the new value BCC KS1S \ Jump to KS1S to skip showing an on-screen bounty for \ this kill (the BCC is effectively a JMP as we just \ passed through a BCS) .n_goodboy 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 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 \ killed (in Cr * 10) 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) .n_hit \ If we get here then we need to apply a hit of strength \ A to the enemy ship STA T \ Store the strength of the hit in T SEC \ Set the C flag so we can do some subtraction LDY #14 \ Fetch byte #14 of the enemy ship's blueprint into A, LDA (XX0),Y \ which gives the ship's maximum energy/shields AND #7 \ Reduce the maximum energy/shields figure to the range \ 0-7 SBC T \ Subtract the hit strength from the maximum shields, so \ A = ship energy - hit strength BCS n_kill \ If the subtraction didn't underflow, then the hit was \ weaker than the ship's shields, so jump to n_kill \ with the C flag set to indicate that the ship has \ survived the attack \BCC n_defense \ These instructions are commented out in the original \LDA #&FF \ source \.n_defense CLC \ Otherwise the hit was stronger than the enemy shields, ADC INWK+35 \ so the ship's energy level needs to register some STA INWK+35 \ damage. A contains a negative number whose magnitude \ is the amount by which the attack is greater than the \ shield defence, so we can simply add this figure to \ the ship's energy levels in the ship's byte #35 to \ reduce the energy by the amount that the attack was \ stronger than the defence (i.e. the shields absorb the \ amount of energy that is defined in the blueprint, and \ the rest of the hit makes it through to damage the \ energy levels) BCS n_kill \ Adding this negative number is the same as subtracting \ a positive number, so having the C flag set indicates \ that the subtraction didn't underflow - in other words \ the damage isn't greater than the energy levels, and \ the ship has survived the hit. In this case we jump to \ n_kill with the C flag set to indicate that the ship \ has survived the attack JSR TA87+3 \ If we get here then the ship has not survived the \ attack, so call TA87+3 to set bit 7 of the ship's byte \ #31, which marks the ship as being killed .n_kill RTS \ Return from the subroutine with the C flag set if the \ ship has survived the onslaught, or clear if it has \ been destroyed .MAC1 LDA TYPE \ If the ship we are processing is a planet or sun, BMI MA27 \ jump to 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 processingName: Main flight loop (Part 12 of 16) [Show more] 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 shipsContext: See this subroutine in context in the source code 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: * 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
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Subroutine FAROF (category: Maths (Geometry))
Compare x_hi, y_hi and z_hi with 224
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Subroutine KS1 (category: Universe)
Remove the current ship from our local bubble of universe
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Label KS1S is local to this routine
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Subroutine LL9_FLIGHT (category: Drawing ships)
Draw a ship (flight version)
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Label MA27 is local to this routine
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Label MAC1 is local to this routine
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Entry point MAL1 in subroutine Main flight loop (Part 4 of 16) (category: Main loop)
Marks the beginning of the ship analysis loop, so we can jump back here from part 12 of the main flight loop to work our way through each ship in the local bubble. We also jump back here when a ship is removed from the bubble, so we can continue processing from the next ship
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Subroutine MCASH (category: Maths (Arithmetic))
Add an amount of cash to the cash pot
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Subroutine MESS (category: Flight)
Display an in-flight message
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Entry point TA87+3 in subroutine TACTICS (Part 1 of 7) (category: Tactics)
Set bit 7 of the ship's byte #31, which marks the ship as being killed, and return from the subroutine
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Temporary storage, used to store the address of a ship blueprint. For example, it is used when we add a new ship to the local bubble in routine NWSHP, and it contains the address of the current ship's blueprint as we loop through all the nearby ships in the main flight loop
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Label n_badboy is local to this routine
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Label n_bitlegal is local to this routine
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Label n_goodboy is local to this routine
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Label n_kill is local to this routine