73 lines
1.2 KiB
ArmAsm
73 lines
1.2 KiB
ArmAsm
;=======================================
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; hgr_vertical scroll_down
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;=======================================
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; scrolls from $6000 to page1
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; jumps increments of 8 for speed
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;=======================================
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hgr_vertical_scroll_down_left:
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; lda #0
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; beq hgr_vertical_scroll_down_common
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hgr_vertical_scroll_down_right:
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; lda #20
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hgr_vertical_scroll_down_common:
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; sta vscroll_down_offset_smc+1
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hgr_vertical_scroll_down:
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ldx #183 ; start at bottom
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outer_vscroll_down_loop:
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lda hposn_low,X ; get page1 address
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sta INL ; set as output
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lda hposn_high,X
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sta INH
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txa ; get address of X+8
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clc ; and set as output
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adc #8
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tay
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lda hposn_low,y
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sta OUTL
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lda hposn_high,Y
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sta OUTH
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ldy #29 ; only scroll from 9..29
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inner_vscroll_down_loop:
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lda (INL),Y
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sta (OUTL),Y
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dey
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cpy #9
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bpl inner_vscroll_down_loop
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dex
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cpx #$FF
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bne outer_vscroll_down_loop
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;================================
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; copy in off screen
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; for now assume all white
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ldx #7 ; start at top
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outer_vscroll_down_loop2:
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lda hposn_low,X
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sta OUTL
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lda hposn_high,X
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sta OUTH
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ldy #39
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lda #$7f
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inner_vscroll_down_loop2:
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sta (OUTL),Y
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dey
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bpl inner_vscroll_down_loop2
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dex
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bpl outer_vscroll_down_loop2
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rts
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