81 lines
2.5 KiB
NASM
81 lines
2.5 KiB
NASM
; Currently statusIntro0 is the same as statusIntro1
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; statusIntro1 has just been reserved for future use
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statusIntro0:
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statusIntro1:
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; Decrement interrupt divider for the intro
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ldx introCounter
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dex
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stx introCounter
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cpx #0
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beq status1do ; if divider is 0, then do status1do ...
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rts ; ... else just do nothing and return
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status1do:
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; Reset introCounter
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ldx #5
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stx introCounter
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; I want to print strings at different columns to make them
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; bounce across the screen, so take last introX and add introXinc,
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; then print string at that point. If introX is too far right, then
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; set introXinc as #$ff (equals -1) so next time introX will be
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; decremented by 1. And then, if introX is too far left, then
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; set introXinc as #$01 so next time will be moved to right again.
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lda introX
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clc
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adc introXinc ; this is #$01 or #$0ff, so actually it is +1 or -1
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sta introX
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cmp #19 ; am I too far right?
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beq status1setSX ; if yes, set SX (left)
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cmp #0 ; am I too far left?
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beq status1setDX ; if yes, set DX (right)
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jmp status1okset ; else do nothing (aka, next time re-use current
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; increment value)
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status1setDX:
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lda #$01 ; set introXinc as +1
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sta introXinc
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jmp status1okset
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status1setSX:
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lda #$ff ; set introXinc as -1
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sta introXinc
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jmp status1okset
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status1okset:
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; Print "SNAKE BY GIOMBA" (see above for pointer details)
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lda #<intro0string
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sta srcStringPointer
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lda #>intro0string
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sta srcStringPointer + 1
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; $0428 is 2nd line (previously filled with color shades by reset routine)
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lda #$28
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clc
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adc introX ; just add X, to make it look like it has moved
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sta dstScreenPointer
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lda #$04
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sta dstScreenPointer + 1
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jsr printString
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; Print "PRESS SPACE TO PLAY"
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lda #<intro1string
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sta srcStringPointer
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lda #>intro1string
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sta srcStringPointer + 1
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; $0478 is 4th line (previously filled with color shades by reset routine)
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; add #19, then sub introX will make it move to other way of 2nd line
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lda #$78
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clc
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adc #19 ; add #19
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sec
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sbc introX ; sub introX
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sta dstScreenPointer
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lda #$04
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sta dstScreenPointer + 1
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jsr printString
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; Some considerations on speed:
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; yes, maybe I should have put the string chars once in screen text memory
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; and then move it left and right. Should re-think about this.
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; For now, just return.
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rts
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