circle.mos

% STD RAS:0

; Read input radius
!ICO ? NIP <- #HLT
; Read a word from the input and write it to
; the printer
radius <- IDA
MUX <- radius
MUY <- radius
radius <- UPL

; Start at 0,0
RAP <- #0

; Distance check
loop:
point_x <- RAX
point_y <- RAY

; Quick check if we are at the border of the image,
; as these pixels are always outside the circle
checkx:
ALX <- point_x
ALY <- #255
EQU ? NIP <- #outside
ALX <- point_x
ALY <- #0
EQU ? NIP <- #outside
NIP <- #checky

checky:
ALX <- point_y
ALY <- #255
EQU ? NIP <- #outside
ALX <- point_y
ALY <- #0
EQU ? NIP <- #outside
NIP <- #cont

; Had some issues with different calculations results when
; pixel locations were < center and > center, so divided this in two parts
; so that I didn't have to debug the issue
cont:
ALX <- point_x
ALY <- center
UGT ? NIP <- #sub_x_large
NIP <- #sub_x_small

sub_x_small: ; x <= 128
ALX <- center
ALY <- point_x
dist_x <- DIF    ; 128 - x
NIP <- #sub_x

sub_x_large: ; x > 128
ALX <- point_x
ALY <- center
dist_x <- DIF ; x - 128
NIP <- #sub_x

sub_x: ; sub x is done
FPX <- FIF <- dist_x
FPY <- FIF <- #2
dist_x <- FFI <- FEX

ALX <- point_y
ALY <- center
UGT ? NIP <- #sub_y_large
NIP <- #sub_y_small

sub_y_small: ; y <= 128
ALX <- center
ALY <- point_y
dist_y <- DIF    ; 128 - y
NIP <- #sub_y

sub_y_large: ; y > 128
ALX <- point_y
ALY <- center
dist_y <- DIF
NIP <- #sub_y

sub_y: ; sub y is done
FPX <- FIF <- dist_y
FPY <- FIF <- #2
dist_y <- FFI <- FEX
NIP <- #square

square:
ALX <- dist_x
ALY <- dist_y
dist <- SUM

ALX <- dist
ALY <- #0
EQU ? NIP <- #outside

ALX <- dist
ALY <- radius
ULT ? NIP <- #inside
NIP <- #outside


inside:
RAI <- #12
NIP <- #check

outside:
RAI <- #0
NIP <- #check

check:
RAP ? NIP <- #loop
RAX <- center
RAY <- center
RAW <- #12
RAD <- #0
NIP <- #HLT


center: 128
dist: 0
dist_x: 0
dist_y: 0
radius: 0
point_x: 0
point_y: 0