82 lines
1.5 KiB
NASM
82 lines
1.5 KiB
NASM
; load new level on the screen
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statusLevelSelect:
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; initialize video pointer with first video memory address
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; (skip first line, used for the status bar)
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ldy #39
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sty levelVideoPointer
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ldy #$04
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sty levelVideoPointer + 1
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ldy #39
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sty levelColorPointer
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ldy #$d8
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sty levelColorPointer + 1
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; Level data is compressed with RLE. Array example:
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; +---+---+---+---+--..--+---+---+
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; | T | N | T | N | .. | 0 | 0 |
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; +---+---+---+---+--..--+---+---+
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; T tile char
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; N count (how many repeated tile chars)
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; 0 end of level
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writeLevelLoop:
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; read `T`
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ldy #0
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lda (levelPointer),y
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sta levelT
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; read `N`
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iny
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lda (levelPointer),y
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sta levelN
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; increment array pointer
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iny
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tya
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tax
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lda #levelPointer
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sta nextPointerPointer
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jsr nextPointer
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; check for array end
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lda levelN
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cmp #0
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beq writeLevelEnd
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; retrieve `N` and put in Y
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ldy levelN
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; unpack char from RLE to the screen
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writeLevelElement:
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lda levelT
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sta (levelVideoPointer),y
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; tiles colors can be found in an array
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; position in array = tile value - $60
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sec
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sbc #$60
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tax
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lda tilesColors,x
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sta (levelColorPointer),y
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dey
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bne writeLevelElement
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; increment dest video memory pointer
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lda #levelVideoPointer
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sta nextPointerPointer
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ldx levelN
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jsr nextPointer
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lda #levelColorPointer
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sta nextPointerPointer
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ldx levelN
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jsr nextPointer
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jmp writeLevelLoop
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writeLevelEnd:
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lda #ST_PLAY
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sta status
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rts
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