205 lines
2.8 KiB
ArmAsm
205 lines
2.8 KiB
ArmAsm
; horizontal star wipe
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; initial code = 164 bytes
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GBASL = $26
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GBASH = $27
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BASL = $28
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BASH = $29
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OFFSET_POINTER = $FE
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LINE = $FF
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SET_GR = $C050
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SET_TEXT = $C051
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FULLGR = $C052
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TEXTGR = $C053
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PAGE0 = $C054
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PAGE1 = $C055
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LORES = $C056 ; Enable LORES graphics
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HIRES = $C057 ; Enable HIRES graphics
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PLOT = $F800 ;; PLOT AT Y,A
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PLOT1 = $F80E ;; PLOT at (GBASL),Y (need MASK to be $0f or $f0)
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HLINE = $F819 ;; HLINE Y,$2C at A
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VLINE = $F828 ;; VLINE A,$2D at Y
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CLRSCR = $F832 ;; Clear low-res screen
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CLRTOP = $F836 ;; clear only top of low-res screen
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GBASCALC= $F847 ;; take Y-coord/2 in A, put address in GBASL/H ( a trashed, C clear)
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SETCOL = $F864 ;; COLOR=A
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SETTXT = $FB36
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SETGR = $FB40
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BASCALC = $FBC1 ; Y-Coord in A, address in BASL/H, X,Y preserved
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WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
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;================================
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; Clear screen and setup graphics
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;================================
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horiz:
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jsr SETGR ; set lo-res 40x40 mode
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bit SET_GR
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bit FULLGR ; make it 40x48
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lda #3
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sta LINE
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lda #0
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sta OFFSET_POINTER
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forever_loop:
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lda #$0
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sta OFFSET_POINTER
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ldx #0
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big_loop:
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txa
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pha
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jsr BASCALC
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ldy #39
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ldx OFFSET_POINTER
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hlin:
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tya
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; if signed (y>offset) && (y<endoffset) draw
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; if signed (y<=offset) || (y>endoffset) don't draw
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clc
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sbc offsets,X
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bvs gurg
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eor #$80
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gurg:
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bpl skip_pixel ; neg if A<=offset
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tya
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clc
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sbc endoffsets,X
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bvs gurg2
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eor #$80
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gurg2:
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bmi skip_pixel ; neg if A<=endoffset
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color_smc:
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lda #$3b
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jmp blah ; TODO: USE BIT TRICK
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skip_pixel:
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lda #$0 ;
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blah:
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sta (BASL),Y
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dey
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bpl hlin
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lda #$bb
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sta color_smc+1
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;==========================================
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; draw star at beginning of line
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lda offsets,X
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bmi skip_star
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clc
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lda BASL
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adc offsets,X
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sta BASL
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ldx LINE
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ldy #7 ; 8-bits wide
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lda star_bitmap-1,X ; get low bit of bitmap into carry
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draw_line_loop:
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lsr
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pha
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bcc its_transparent
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lda #$ff ; white
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sta (BASL),Y ; draw on screen
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its_transparent:
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pla
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dey
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bpl draw_line_loop
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skip_star:
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; see if new line
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ldx OFFSET_POINTER
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dec LINE
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bne not3
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lda #$b3
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sta color_smc+1
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dec offsets,X
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dec endoffsets,X
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inc OFFSET_POINTER
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lda #3
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sta LINE
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not3:
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;==========================
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pla
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tax
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inx
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cpx #24
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bne big_loop
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; set/flip pages
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; we want to flip pages and then draw to the offscreen one
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;flip_pages:
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; ldx #0 ; x already 0
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; lda draw_page_smc+1 ; DRAW_PAGE
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;; beq done_page
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; inx
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;done_page:
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; ldy PAGE0,X ; set display page to PAGE1 or PAGE2
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; eor #$4 ; flip draw page between $400/$800
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; sta draw_page_smc+1 ; DRAW_PAGE
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lda #80
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jsr WAIT
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jmp forever_loop
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offsets:
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.byte 5,4,3,2,1,2,3,4,5
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endoffsets:
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.byte 30,20,10,20,30,40,50,12
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; 76543210
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; @
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; @@@@@
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; @ @
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star_bitmap:
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.byte $50
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.byte $f8
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.byte $20
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; for bot
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jmp horiz
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