304 lines
3.0 KiB
ArmAsm
304 lines
3.0 KiB
ArmAsm
; VGI_Circles
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XX = TEMP0
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MINUSXX = TEMP1
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YY = TEMP2
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MINUSYY = TEMP3
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D = TEMP4
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COUNT = TEMP5
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;========================
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; VGI circle
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;========================
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VGI_CCOLOR = P0
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VGI_CX = P1
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VGI_CY = P2
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VGI_CR = P3
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vgi_circle:
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ldx VGI_CCOLOR
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lda COLORTBL,X
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sta HGR_COLOR
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;===============================
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; draw circle
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;===============================
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; draw circle at (CX,CY) of radius R
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; signed 8-bit math so problems if R > 64?
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; XX=0 YY=R
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; D=3-2*R
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; GOTO6
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lda #0
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sta XX
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lda VGI_CR
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sta YY
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lda #3
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sec
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sbc VGI_CR
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sbc VGI_CR
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sta D
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jmp do_plots
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circle_loop:
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; X=X+1
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inc XX
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; IF D>0 THEN Y=Y-1:D=D+4*(X-Y)+10
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lda D
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bmi else
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dec YY
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lda XX
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sec
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sbc YY
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asl
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asl
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clc
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adc D
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adc #10
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jmp store_D
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else:
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; ELSE D=D+4*X+6
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lda XX
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asl
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asl
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clc
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adc D
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adc #6
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store_D:
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sta D
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do_plots:
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; setup constants
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lda XX
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eor #$FF
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sta MINUSXX
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inc MINUSXX
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lda YY
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eor #$FF
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sta MINUSYY
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inc MINUSYY
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; HPLOT CX+X,CY+Y
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; HPLOT CX-X,CY+Y
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; HPLOT CX+X,CY-Y
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; HPLOT CX-X,CY-Y
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; HPLOT CX+Y,CY+X
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; HPLOT CX-Y,CY+X
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; HPLOT CX+Y,CY-X
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; HPLOT CX-Y,CY-X
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; calc X co-ord
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lda #7
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sta COUNT
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pos_loop:
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lda COUNT
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and #$4
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lsr
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tay
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lda COUNT
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lsr
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bcc xnoc
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iny
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xnoc:
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lda VGI_CX
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clc
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adc XX,Y
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tax
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; calc y co-ord
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lda COUNT
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lsr
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eor #$2
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tay
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lda VGI_CY
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clc
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adc XX,Y
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ldy #0
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jsr HPLOT0 ; plot at (Y,X), (A)
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dec COUNT
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bpl pos_loop
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; IFY>=XTHEN4
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lda YY
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cmp XX
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bcs circle_loop
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jmp vgi_loop
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;========================
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; VGI circle
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;========================
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; VGI_CCOLOR = P0
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; VGI_CX = P1
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; VGI_CY = P2
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; VGI_CR = P3
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vgi_filled_circle:
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ldx VGI_CCOLOR
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lda COLORTBL,X
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sta HGR_COLOR
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;===============================
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; draw filled circle
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;===============================
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; draw filled circle at (CX,CY) of radius R
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; signed 8-bit math so problems if R > 64?
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; XX=0 YY=R
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; D=3-2*R
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; GOTO6
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lda #0
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sta XX
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lda VGI_CR
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sta YY
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lda #3
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sec
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sbc VGI_CR
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sbc VGI_CR
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sta D
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jmp do_filled_plots
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filled_circle_loop:
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; X=X+1
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inc XX
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; IF D>0 THEN Y=Y-1:D=D+4*(X-Y)+10
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lda D
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bmi filled_else
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dec YY
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lda XX
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sec
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sbc YY
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asl
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asl
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clc
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adc D
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adc #10
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jmp store_filled_D
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filled_else:
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; ELSE D=D+4*X+6
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lda XX
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asl
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asl
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clc
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adc D
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adc #6
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store_filled_D:
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sta D
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do_filled_plots:
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; setup constants
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lda XX
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eor #$FF
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sta MINUSXX
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inc MINUSXX
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lda YY
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eor #$FF
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sta MINUSYY
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inc MINUSYY
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; HPLOT CX+X,CY+Y
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; HPLOT CX-X,CY+Y
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; HPLOT CX+X,CY-Y
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; HPLOT CX-X,CY-Y
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; HPLOT CX+Y,CY+X
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; HPLOT CX-Y,CY+X
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; HPLOT CX+Y,CY-X
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; HPLOT CX-Y,CY-X
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lda #3
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sta COUNT
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filled_pos_loop:
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; calc left side
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; calc X co-ord
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lda COUNT
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ora #$1
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eor #$2
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tay
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lda VGI_CX
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clc
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adc XX,Y
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tax
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; calc y co-ord
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ldy COUNT
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lda VGI_CY
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clc
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adc XX,Y
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ldy #0
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; pha ; save Y value for later
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jsr HPLOT0 ; plot at (Y,X), (A)
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; calc right side
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lda COUNT
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and #$2
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eor #$2
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tay
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lda XX,Y
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asl
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ldy #0
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ldx #0
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jsr HLINRL ; plot relative (X,A), (Y)
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; so in our case (0,XX*2),0
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dec COUNT
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bpl filled_pos_loop
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; IFY>=XTHEN4
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lda YY
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cmp XX
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bcs filled_circle_loop
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jmp vgi_loop
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