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Elite on the BBC Micro and NES

Main loop: Main game loop (Part 6 of 6)

[BBC Micro cassette version]

Name: Main game loop (Part 6 of 6) [Show more] Type: Subroutine Category: Main loop Summary: Process non-flight key presses (red function keys, docked keys) 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: This subroutine is called as follows: * BAY calls via FRCE * TT219 calls via FRCE * Main game loop (Part 4 of 6) calls via tha

This is the second half of the minimal game loop, which we iterate when we are docked. This section covers the following: * Process more key presses (red function keys, docked keys etc.) It also supports joining the main loop with a key already "pressed", so we can jump into the main game loop to perform a specific action. In practice, this is used when we enter the docking bay in BAY to display Status Mode (red key f8), and when we finish buying or selling cargo in BAY2 to jump to the Inventory (red key f9).
Other entry points: FRCE The entry point for the main game loop if we want to jump straight to a specific screen, by pretending to "press" a key, in which case A contains the internal key number of the key we want to "press" tha Consider spawning a Thargoid (22% chance)
.FRCE JSR TT102 \ Call TT102 to process the key pressed in A LDA QQ12 \ Fetch the docked flag from QQ12 into A BNE MLOOP \ If we are docked, loop back up to MLOOP just above \ to restart the main loop, but skipping all the flight \ and spawning code in the top part of the main loop JMP TT100 \ Otherwise jump to TT100 to restart the main loop from \ the start .tha JSR DORND \ Set A and X to random numbers CMP #200 \ If A < 200 (78% chance), skip the next instruction BCC P%+5 JSR GTHG \ Call GTHG to spawn a Thargoid ship and a Thargon \ companion JMP MLOOP \ Jump back into the main loop at MLOOP, which is just \ after the ship-spawning section