mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-07-15 19:29:07 +00:00
155 lines
1.9 KiB
ArmAsm
155 lines
1.9 KiB
ArmAsm
; orb
|
|
|
|
; this was found accidentally when trying to draw circles
|
|
; it's doing Bresenham circle algo I think, which does weird
|
|
; things when radius=0
|
|
|
|
orb:
|
|
; a=0, y=0 here
|
|
|
|
tax ; x=0
|
|
|
|
dey ; set init color to white
|
|
sty HGR_COLOR ; set init color to white
|
|
|
|
draw_next:
|
|
stx R
|
|
|
|
;===============================
|
|
; draw circle
|
|
;===============================
|
|
; draw circle at (CX,CY) of radius R
|
|
; signed 8-bit math so problems if R > 64?
|
|
|
|
lda #0
|
|
sta XX ; XX = 0
|
|
|
|
stx YY ; YY =R (X is R here)
|
|
|
|
lda #3 ; D=3-2*R
|
|
sec
|
|
sbc R
|
|
sbc R
|
|
sta D
|
|
|
|
; always odd, never zero
|
|
|
|
bne do_plots ; bra skip ahead first time through
|
|
|
|
circle_loop:
|
|
inc XX ; XX=XX+1
|
|
|
|
lda XX ; XX is common both paths
|
|
ldy #6 ; default path add 6
|
|
|
|
; IF D>0 THEN Y=Y-1:D=D+4*(X-Y)+10
|
|
bit D ; check if negative w/o changing A
|
|
bmi d_negative
|
|
|
|
dec YY ; YY=YY-1
|
|
|
|
d_positive:
|
|
; D=D+4*(XX-YY)+10
|
|
|
|
; XX is already in A
|
|
sec
|
|
sbc YY
|
|
ldy #10
|
|
d_negative:
|
|
; ELSE D=D+4*(XX)+6
|
|
common_D:
|
|
sty DADD
|
|
asl
|
|
asl
|
|
clc
|
|
adc DADD
|
|
adc D
|
|
sta D
|
|
|
|
do_plots:
|
|
; setup constants
|
|
|
|
lda XX
|
|
eor #$FF
|
|
sta MINUSXX
|
|
inc MINUSXX
|
|
|
|
lda YY
|
|
eor #$FF
|
|
sta MINUSYY
|
|
inc MINUSYY
|
|
|
|
; HPLOT CX+X,CY+Y
|
|
; HPLOT CX-X,CY+Y
|
|
; HPLOT CX+X,CY-Y
|
|
; HPLOT CX-X,CY-Y
|
|
; HPLOT CX+Y,CY+X
|
|
; HPLOT CX-Y,CY+X
|
|
; HPLOT CX+Y,CY-X
|
|
; HPLOT CX-Y,CY-X
|
|
|
|
lda #3
|
|
sta COUNT
|
|
pos_loop:
|
|
|
|
; calc left side
|
|
|
|
; calc X co-ord
|
|
|
|
lda COUNT
|
|
ora #$1
|
|
eor #$2
|
|
tax
|
|
; lda CX
|
|
|
|
|
|
lda #128
|
|
clc
|
|
adc XX,X
|
|
tax
|
|
|
|
; calc y co-ord
|
|
|
|
ldx COUNT
|
|
; lda CY
|
|
lda #96
|
|
clc
|
|
adc XX,X
|
|
|
|
ldy #0
|
|
|
|
jsr HPLOT0 ; plot at (Y,X), (A)
|
|
|
|
|
|
; calc right side
|
|
lda COUNT
|
|
and #$2
|
|
eor #$2
|
|
tax
|
|
lda XX,X
|
|
asl
|
|
|
|
jsr combo_hlinrl ; plot relative (X,A), (Y)
|
|
; so in our case (0,XX*2),0
|
|
|
|
|
|
dec COUNT
|
|
bpl pos_loop
|
|
|
|
; IF YY>=XX THEN 4
|
|
; equivelant to IF XX<YY
|
|
; but sadly appears we need IF XX<=YY for same effect
|
|
lda YY
|
|
cmp XX
|
|
bcs circle_loop
|
|
|
|
done:
|
|
ldx R
|
|
inx ; increment radius
|
|
jsr HCOLOR1 ; use as color
|
|
|
|
cpx #48 ; run until R=48
|
|
bne draw_next ; loop (GOTO 1)
|
|
|
|
rdone:
|