Main loop: Main game loop (Part 1 of 6)

       Name: Main game loop (Part 1 of 6)                            [Show more]
       Type: Subroutine
   Category: Main loop
    Summary: Spawn a trader (a Cobra Mk III, Python, Boa or Anaconda)
  Deep dive: Program flow of the main game loop
             Ship data blocks
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


 This is part of the main game loop. This is where the core loop of the game
 lives, and it's in two parts. The shorter loop (just parts 5 and 6) is
 iterated when we are docked, while the entire loop from part 1 to 6 iterates
 if we are in space.

 This section covers the following:

   * Spawn a trader, i.e. a Cobra Mk III, Python, Boa or Anaconda, with a 50%
     chance of it having a missile, a 50% chance of it having an E.C.M., a 50%
     chance of it docking and being aggressive if attacked, a speed between 16
     and 31, and a gentle clockwise roll

 We call this from within the main loop.


.MTT4

 JSR DORND              ; Set A and X to random numbers

 LSR A                  ; Clear bit 7 of our random number in A and set the C
                        ; flag to bit 0 of A, which is random

 STA INWK+32            ; Store this in the ship's AI flag, so this ship does
                        ; not have AI

 STA INWK+29            ; Store A in the ship's roll counter, giving it a
                        ; clockwise roll (as bit 7 is clear), and a 1 in 127
                        ; chance of it having no damping

 ROL INWK+31            ; Set bit 0 of the ship's missile count randomly (as the
                        ; C flag was set), giving the ship either no missiles or
                        ; one missile

 AND #15                ; Set the ship speed to our random number, set to a
 ADC #10                ; minimum of 10 and a maximum of 26 (as the C flag is
 STA INWK+27            ; also randomly set)

 JSR DORND              ; Set A and X to random numbers, plus the C flag

 BMI nodo               ; If A is negative (50% chance), jump to nodo to skip
                        ; the following

                        ; If we get here then we are going to spawn a ship that
                        ; is minding its own business and trying to dock

 LDA INWK+32            ; Set bits 6 and 7 of the ship's AI flag, to make it
 ORA #%11000000         ; aggressive if attacked, and enable its AI
 STA INWK+32

 LDX #%00010000         ; Set bit 4 of the ship's NEWB flags, to indicate that
 STX NEWB               ; this ship is docking

.nodo

 AND #2                 ; If we jumped here with a random value of A from the
                        ; BMI above, then this reduces A to a random value of
                        ; either 0 or 2; if we didn't take the BMI and made the
                        ; ship hostile, then A will be 0

 ADC #CYL               ; Set A = A + C + #CYL
                        ;
                        ; where A is 0 or 2 and C is 0 or 1, so this gives us a
                        ; ship type from the following: Cobra Mk III, Python,
                        ; Boa or Anaconda

 CMP #HER               ; If A is not the ship type of a rock hermit, jump to
 BNE game1              ; game1 to skip the following instruction

 LDA #CYL               ; This is a rock hermit, so set A = #CYL so we spawn a
                        ; Cobra Mk III

.game1

 JSR NWSHP              ; Add a new ship of type A to the local bubble and fall
                        ; through into the main game loop again

 JMP MLOOP              ; Jump down to MLOOP to do some end-of-loop tidying and
                        ; restart the main loop