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A C64 Game - Step 68

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Endurion

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Added a first version of Sams dark force, making it visible. It's not looking quite what I wanted it, but it is getting there.

step68.png

To make things faster for removal of the beam we calc the required length and direction of the beam:


;redraw black beam
ldx PARAM6

ldy SPRITE_CHAR_POS_Y,x
dey
sty SAM_FORCE_START_Y
lda SCREEN_LINE_OFFSET_TABLE_LO,y
sta ZEROPAGE_POINTER_1
sta ZEROPAGE_POINTER_2
lda SCREEN_LINE_OFFSET_TABLE_HI,y
sta ZEROPAGE_POINTER_1 + 1
clc
adc #( ( SCREEN_COLOR - SCREEN_CHAR ) >> 8 )
sta ZEROPAGE_POINTER_2 + 1

ldy SPRITE_CHAR_POS_X,x
lda SPRITE_DIRECTION,x
sta PARAM1

lda #0
sta SAM_FORCE_LENGTH

ldx SPRITE_HELD
dex

-
lda #253
sta (ZEROPAGE_POINTER_1),y
lda #6
sta (ZEROPAGE_POINTER_2),y

inc SAM_FORCE_LENGTH

lda PARAM1
bne ++

iny
jmp +

++
dey

+
tya
cmp SPRITE_CHAR_POS_X,x
bne -

;store for later removal
ldx PARAM6
lda PARAM1
bne +

;going right
lda SPRITE_CHAR_POS_X,x
sta SAM_FORCE_START_X
jmp ++


+
;going left
sty SAM_FORCE_START_X
inc SAM_FORCE_START_X

++
ldy SPRITE_HELD
dey


The beam needs to be removed once Sam stops pressing the fire button or he or his enemy dies. Aren't we glad that we already have a back buffer we can use to restore the background properly?


;restore play field from force beam
!zone RemoveForceBeam
RemoveForceBeam
ldy SAM_FORCE_START_Y

lda SCREEN_LINE_OFFSET_TABLE_LO,y
sta ZEROPAGE_POINTER_1
sta ZEROPAGE_POINTER_2
sta ZEROPAGE_POINTER_3
sta ZEROPAGE_POINTER_4
lda SCREEN_LINE_OFFSET_TABLE_HI,y
sta ZEROPAGE_POINTER_1 + 1
clc
adc #( ( SCREEN_COLOR - SCREEN_CHAR ) & 0xff00 ) >> 8
sta ZEROPAGE_POINTER_2 + 1
sec
sbc #( ( SCREEN_COLOR - SCREEN_BACK_CHAR ) & 0xff00 ) >> 8
sta ZEROPAGE_POINTER_3 + 1
sec
sbc #( ( SCREEN_BACK_CHAR - SCREEN_BACK_COLOR ) & 0xff00 ) >> 8
sta ZEROPAGE_POINTER_4 + 1

ldy SAM_FORCE_START_X

-
lda (ZEROPAGE_POINTER_3),y
sta (ZEROPAGE_POINTER_1),y
lda (ZEROPAGE_POINTER_4),y
sta (ZEROPAGE_POINTER_2),y

iny
dec SAM_FORCE_LENGTH
bne -

rts



So when Sam dies we modify existing code to:


lda SPRITE_HELD
beq +

jsr RemoveForceBeam
lda #0
sta SPRITE_HELD
+



Voila! Carnage made more visible ;)


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5 Comments


I'm already doing so, see Joe Gunn or Soulless :)

Also, on a lemon64 thread Smila (the graphician) put a few screenshots of soon to be worked on projects like Catnipped and Hyperion.
All those however are not done with code and tutorial steps like Supernatural.
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You made Soulless: http://www.psytronik.net/main/index.php?option=com_content&view=article&id=97:soulless&catid=34:commodore-64&Itemid=57 ???

AMAZING!!!!! :D
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Yeah :) The graphic and music are pure gold.

The game itself is quite simple technically and pretty similar to the code here ;)
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