Main loop: Main flight loop (Part 13 of 16)

       Name: Main flight loop (Part 13 of 16)                        [Show more]
       Type: Subroutine
   Category: Main loop
    Summary: Show energy bomb effect, charge shields and energy banks
  Deep dive: Program flow of the main game loop
             Scheduling tasks with the main loop counter
    Context: 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:

   * Show energy bomb effect (if applicable)

   * Charge shields and energy banks (every 7 iterations of the main loop)


.MA18

 LDA BOMB               ; If we set off our energy bomb (see MA24 above), then
 BPL MA77               ; BOMB is now negative, so this skips to MA21 if our
                        ; energy bomb is not going off

 ASL BOMB               ; We set off our energy bomb, so rotate BOMB to the
                        ; left by one place. BOMB was rotated left once already
                        ; during this iteration of the main loop, back at MA24,
                        ; so if this is the first pass it will already be
                        ; %11111110, and this will shift it to %11111100 - so
                        ; if we set off an energy bomb, it stays activated
                        ; (BOMB > 0) for four iterations of the main loop

 BMI MA77               ; If the result has bit 7 set, skip the following
                        ; instruction as the bomb is still going off

 JSR BOMBOFF            ; Our energy bomb has finished going off, so call
                        ; BOMBOFF to turn off the bomb effect

.MA77

 LDA MCNT               ; Fetch the main loop counter and calculate MCNT mod 8,
 AND #7                 ; jumping to MA22 if it is non-zero (so the following
 BNE MA22               ; code only runs every 8 iterations of the main loop)

 LDX ENERGY             ; Fetch our ship's energy levels and skip to b if bit 7
 BPL b                  ; is not set, i.e. only charge the shields from the
                        ; energy banks if they are at more than 50% charge

 LDX ASH                ; Call SHD to recharge our aft shield and update the
 JSR SHD                ; shield status in ASH
 STX ASH

 LDX FSH                ; Call SHD to recharge our forward shield and update
 JSR SHD                ; the shield status in FSH
 STX FSH

.b

 SEC                    ; Set A = ENERGY + ENGY + 1, so our ship's energy
 LDA ENGY               ; level goes up by 2 if we have an energy unit fitted,
 ADC ENERGY             ; otherwise it goes up by 1

 BCS P%+5               ; If the value of A did not overflow (the maximum
 STA ENERGY             ; energy level is $FF), then store A in ENERGY