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

This code appears in the following versions (click to see it in the source code):

Cassette, Disc (flight), Disc (docked), 6502 Second Processor, Master and Electron

Code variations between these versions are shown below.

       Name: Main game loop (Part 6 of 6)
       Type: Subroutine
   Category: Main loop

Code variation 1 of 6A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Master
Electron
    Summary: Process non-flight key presses (red function keys, docked keys)
    Summary: Process non-flight key presses (FUNC keys, docked keys)

  Deep dive: Program flow of the main game loop


 This is the second half of the minimal game loop, which we iterate when we are
 docked. This section covers the following:

Code variation 2 of 6A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Master
Electron
   * Process more key presses (red function keys, docked keys etc.)
   * Process more key presses (FUNC 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

Code variation 3 of 6A variation in the comments only

Tap on a block to expand it, and tap it again to revert.

Cassette, Flight, Docked, 6502SP, Master
Electron
 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).
 is used when we enter the docking bay in BAY to display Status Mode (FUNC-9),
 and when we finish buying or selling cargo in BAY2 to jump to the Inventory
 (FUNC-0).



 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"

Code variation 4 of 6A variation in the comments only

This variation is blank in the Disc (flight), Disc (docked), 6502 Second Processor, Master and Electron versions.

Cassette
   tha                  Consider spawning a Thargoid (22% chance)


.FRCE

 JSR TT102              \ Call TT102 to process the key pressed in A

Code variation 5 of 6Minor and very low-impact

This variation is blank in the Disc (flight) version.

Tap on a block to expand it, and tap it again to revert.

Cassette, Docked, 6502SP, Electron
Master
 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
 LDA QQ12               \ Fetch the docked flag from QQ12 into A

 BEQ P%+5               \ If we are docked, loop back up to MLOOP just above
 JMP MLOOP              \ 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

Code variation 6 of 6Specific to an individual platform

This variation is blank in the Disc (flight), Disc (docked), 6502 Second Processor, Master and Electron versions.

Cassette
.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