mirror of
https://github.com/deater/dos33fsprogs.git
synced 2025-03-06 18:30:12 +00:00
77 lines
920 B
ArmAsm
77 lines
920 B
ArmAsm
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;================================
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; HGR vscroll
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;================================
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; image to scroll in is in $A000
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hgr_vscroll:
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ldx #191
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stx SCROLL ; SCROLL = 0
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vscroll_loop:
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; for x=0 to 192-SCROLL
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; write 40 bytes of 00
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ldx #0
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vscroll_inner:
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lda hposn_high,X
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sta OUTH
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lda hposn_low,X
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sta OUTL
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ldy #39
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lda #0
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vscroll_line:
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sta (OUTL),Y
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dey
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bpl vscroll_line
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inx
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cpx SCROLL
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bne vscroll_inner
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;====================
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; draw bottom part
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lda #0
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sta SCROLL_OFFSET
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vscroll_bottom:
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stx XSAVE
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ldx SCROLL_OFFSET
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lda hposn_high,X
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clc
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adc #$80 ; ora instead?
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sta INH
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lda hposn_low,X
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sta INL
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inc SCROLL_OFFSET
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ldx XSAVE
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lda hposn_high,X
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sta OUTH
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lda hposn_low,X
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sta OUTL
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ldy #39
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vscroll_bottom_line:
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lda (INL),Y
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sta (OUTL),Y
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dey
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bpl vscroll_bottom_line
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inx
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cpx #192
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bne vscroll_bottom
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;=====================
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; scroll whole screen
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dec SCROLL
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bne vscroll_loop
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rts
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