mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-07-04 08:29:30 +00:00
167 lines
2.4 KiB
ArmAsm
167 lines
2.4 KiB
ArmAsm
; orb
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; this was found accidentally when trying to draw circles
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; it's doing Bresenham circle algo I think, which does weird
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; things when radius=0
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orb:
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; a=0, y=0 here (it's after HGR2)
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tax ; x=0 (set R=0)
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dey ; set init color to white
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sty HGR_COLOR ; set init color to white
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draw_next:
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; X is always R here
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stx R
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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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lda #0
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sta XX ; XX = 0
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stx YY ; YY =R (X is R here)
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lda #3 ; D=3-2*R
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sec
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sbc R
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sbc R
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; D is now in A
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; always odd, never zero
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bne do_plots ; bra skip ahead first time through
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circle_loop:
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inc XX ; XX=XX+1
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lda XX ; XX is common both paths
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ldy #6 ; default path add 6
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; IF D>0 THEN Y=Y-1:D=D+4*(X-Y)+10
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bit D ; check if negative w/o changing A
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bmi d_negative
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dec YY ; YY=YY-1
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d_positive:
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; D=D+4*(XX-YY)+10
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; XX is already in A
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; sec ; saves a byte, seems to be OK?
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sbc YY
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ldy #10
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d_negative:
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; ELSE D=D+4*(XX)+6
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common_D:
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sty DADD
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asl
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asl
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clc
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adc DADD
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adc D
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do_plots:
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; D is always in A here
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sta D
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; setup plus/minus XX/YY
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ldx #2
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plus_minus_loop:
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lda XX,X
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eor #$FF
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sta MINUSXX,X
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inc MINUSXX,X
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dex
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dex
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bpl plus_minus_loop
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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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ldx #3
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pos_loop:
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; calc left side
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; COUNT already in X here
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stx COUNT
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; calc y co-ord
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lda #96 ; center around y=96
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clc
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adc XX,X ; index with COUNT
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tay ; save for later
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; calc x co-ord
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txa ; get count
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ora #$1 ; generate pattern
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eor #$2 ; ???
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tax ; offset in array
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lda #128 ; center around x=128
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clc
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adc XX,X
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tax
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tya ; restore Y co-ordinate
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ldy #0 ; always 0
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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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tax
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lda XX,X
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asl
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jsr combo_hlinrl ; plot relative (X,A), (Y)
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; so in our case (0,XX*2),0
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; X/A/Y saved to zero page
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; X/Y were zero
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ldx COUNT
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dex ; decrement count
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bpl pos_loop
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; IF YY>=XX THEN 4
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; should be equivelant to IF XX<YY
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; but sadly appears we need IF XX<=YY for our initial effect
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lda YY
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cmp XX
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bcs circle_loop
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done:
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ldx R
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inx ; increment radius
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jsr HCOLOR1 ; use as color
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cpx #48 ; run until R=48
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bne draw_next ; loop (GOTO 1)
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rdone:
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