Combat demo: SetupDemoUniverse

       Name: SetupDemoUniverse                                       [Show more]
       Type: Subroutine
   Category: Combat demo
    Summary: Initialise the local bubble of universe for the demo
  Deep dive: The NES combat demo
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DEATH2 calls SetupDemoUniverse
             * SetDemoAutoPlay calls SetupDemoUniverse


.SetupDemoUniverse

 LDY #12                ; Wait until 12 NMI interrupts have passed (i.e. the
 JSR DELAY              ; next 12 VBlanks)

 LDA #0                 ; Set A = 0
 CLC                    ;
 ADC #0                 ; The ADC has no effect, so presumably it was left over
                        ; from a previous version of the code

 STA nmiCounter         ; Reset the NMI counter to zero

 STA nmiTimer           ; Set the NMI timer to zero
 STA nmiTimerLo
 STA nmiTimerHi

 STA hiddenBitplane     ; Set the hidden, NMI and drawing bitplanes to 0
 STA nmiBitplane
 STA drawingBitplane

 LDA #$FF               ; Set soundVibrato = $FF $80 $1B $34 to set the seeds
 STA soundVibrato       ; for the randomised vibrato that's applied to sound
 LDA #$80               ; effects
 STA soundVibrato+1
 LDA #$1B
 STA soundVibrato+2
 LDA #$34
 STA soundVibrato+3

 JSR ResetOptions       ; Reset the game options to their default values

 LDA #0                 ; Set K%+6 to 0 so the random number seeding at the
 STA K%+6               ; start of the main game loop at TT100 proceeds in a
                        ; predictable manner

 STA K%                 ; Set K% to 0 so the random number seeding at the start
                        ; of the main flight loop at M% proceeds in a
                        ; predictable manner

                        ; Fall through into FixRandomNumbers to set the random
                        ; number seeds to a known state