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BBC Micro Elite

Tactics: FRS1

Name: FRS1 [View in context] Type: Subroutine Category: Tactics Summary: Launch a ship straight ahead of us, below the laser sights
This is used in two places: * When we launch a missile, in which case the missile is the ship that is launched ahead of us * When we launch our escape pod, in which case it's our abandoned Cobra Mk III that is launched ahead of us * The fq1 entry point is used to launch a bunch of cargo canisters ahead of us as part of the death screen Arguments: X The type of ship to launch ahead of us Returns: C flag Set if the ship was successfully launched, clear if it wasn't (as there wasn't enough free memory) Other entry points: fq1 Used to add a cargo canister to the universe
.FRS1 { JSR ZINF \ Call ZINF to reset the INWK ship workspace LDA #28 \ Set y_lo = 28 STA INWK+3 LSR A \ Set z_lo = 14, so the launched ship starts out STA INWK+6 \ ahead of us LDA #%10000000 \ Set y_sign to be negative, so the launched ship is STA INWK+5 \ launched just below our line of sight LDA MSTG \ Set A to the missile lock target, shifted left so the ASL A \ slot number is in bits 1-4 ORA #%10000000 \ Set bit 7 and store the result in byte #32, the AI STA INWK+32 \ flag launched ship for the launched ship. For missiles \ this enables AI (bit 7), makes it friendly towards us \ (bit 6), sets the target to the value of MSTG (bits \ 1-4), and sets its lock status as launched (bit 0). \ It doesn't matter what it does for our abandoned \ Cobra, as the AI flag gets overwritten once we return \ from the subroutine back to the ESCAPE routine that \ called FRS1 in the first place .^fq1 LDA #&60 \ Set byte #14 (nosev_z_hi) to 1 (&60), so the launched STA INWK+14 \ ship is pointing away from us ORA #128 \ Set byte #22 (sidev_x_hi) to -1 (&D0), so the launched STA INWK+22 \ ship has the same orientation as spawned ships, just \ pointing away from us (if we set sidev to +1 instead, \ this ship would be a mirror image of all the other \ ships, which are spawned with -1 in nosev and +1 in \ sidev) LDA DELTA \ Set byte #27 (speed) to 2 * DELTA, so the launched ROL A \ ship flies off at twice our speed STA INWK+27 TXA \ Add a new ship of type X to our local bubble of JMP NWSHP \ universe and return from the subroutine using a tail \ call }