Programming the Commodore 64 again: Create a game step by step by Jens Christian Ingvartsen Thomsen

Author:Jens Christian Ingvartsen Thomsen [Thomsen, Jens Christian Ingvartsen]
Language: eng
Format: azw3
Published: 2021-01-16T00:00:00+00:00

#region Increment score

;**************************************************************************

;** Increment score

;**************************************************************************

IncrementScore

sed ​ ​ ;** Set decimal mode

clc ​ ​ ;** Clear carry flag

lda Score ​ ;** Load from score variable

adc #1 ​ ;** Add with carry value 1

sta Score ​ ;** Store in score variable

lda Score+1 ​ ;** Load from score variable + 1

adc #0 ​ ;** Add with carry value 0

sta Score+1 ​ ;** Store in score variable + 1

lda Score+2 ​ ;** Load from score variable + 2

adc #0 ​ ;** Add with carry value 0

sta Score+2 ​ ;** Store in score variable + 2

cld ​ ​ ;** Clear decimal mode

rts ​ ​ ;** Return

#endregion

#region Display lives

;**************************************************************************

;** Display lives

;**************************************************************************

DisplayLives

lda Lives ​ ;** Load from lives variable

sta Lives_Score ​ ;** Store in lives score variable

rts ​ ​ ;** Return

#endregion

#region Decrement lives

;**************************************************************************

;** Decrement lives

;************************************************************ **************

DecrementLives

ldx Lives ​ ;** Load from lives variable

dex ​ ​ ;** Decrement x register value with 1

stx Lives ​ ;** Store in lives variable

rts ​ ​ ;** Return

#endregion

#region Play explosion animation

;***************************************

;** Play explosion animation

;***************************************

PlayExplosionAnimation

ldx ExplosionIndex ​ ;** Load from explosion index variable

inx ​ ​ ;** Increment x register with 1

stx ExplosionIndex ​ ;** Store in explosion index variable

cpx #$8F ​ ;** Compare with value $8F

bne @continueExplosion ​ ;** Branch if not equal to @continueExplosion label

ldx #0 ​ ​ ;** Load value 0

stx ExplosionPlaying ​ ;** Store in explosion playing variable

stx SP2X ​ ;** Store in sprite 2 x position address

stx SP2Y ​ ;** Store in sprite 2 y position address

ldx #$8A ​ ;** Load value $8A

stx ExplosionIndex ​ ;** Store in explosion index variable

@continueExplosion

jsr SetCurrentExplosionSprite ​ ;** Gosub to set current explosion sprite

rts ​ ​ ;** Return

#endregion

#region Set current explosion sprite

;***************************************

;** Set current explosion sprite

;***************************************

SetCurrentExplosionSprite

PointToSpriteData ExplosionIndex, SSDP2 ;** Set current explosion sprite

rts ​ ​ ;** Return

#endregion

#region Set current portal sprite

;***************************************

;** Set current portal sprite

;***************************************

SetCurrentPortalSprite

PointToSpriteData PortalIndex, SSDP3 ;** Set current portal sprite

rts ​ ​ ;** Return

#endregion

#region Wait for explosion

;***************************************

;** Wait for explosion

;***************************************

WaitForExplosion

ldx #25 ​ ;** Load value 25

@waitExplosion1

ldy #255 ​ ;** Load value 255

@waitExplosion2

dey ​ ​ ;** Decrement y register with value 1

cpy #0 ​ ;** Compare with value 0

bne @waitExplosion2 ​ ;** Branch if not equal to @waitExplosion2 label

dex ​ ​ ;** Decrement x register with value 1

cpx #0 ​ ;** Compare with value 0

bne @waitExplosion1 ​ ;** Branch if not equal to @waitExplosion1 label

rts ​ ​ ;** Return

#endregion

#region Play explosion sound

;***************************************

;** Play explosion sound

;***************************************

PlayExplosionSound

lda #15 ​ ;** Load value 15

sta SIGVOL ​ ;** Store in volume register

lda #0 ​ ​ ;** Load value 0

sta FRELO1 ​ ;** Store in frequency low byte register

lda #30 ​ ;** Load value 30

sta FREHI1 ​ ;** Store in frequency hi byte register

lda #12 ​ ;** Load value 12

sta ATDCY1 ​ ;** Store in attack/decay register

lda #5 ​ ​ ;** Load value 5

sta SURELI ​ ;** Store in sustain/release register

lda #0 ​ ​ ;** Load value 0

sta VCREG1 ​ ;** Store in pulse waveform register

lda #129 ​ ;** Load value 129

sta VCREG1 ​ ;** Store in pulse waveform register

rts ​ ​ ;** Return

#endregion

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