Draw a semicircle in Netlogo - netlogo

Question

I want to create a semicircle, the center of my semicircle is at the end of the world, for example I want that the center of my semicircle is in the 50,20 position, and goes from 20 to -20.
I try with this, but I got an exception:
The point [ 60 , 20 ] is outside of the boundaries of the world and
wrapping is not permitted in one or both directions.
to mysemicircle
let cx 50 ;; x coordinate of patch you want to circle
let cy 20 ;; y coordinate of patch you want to circle
let r 10 ;; radius of the circle you want
let p2r ( 2 * pi * r ) ;; get circumference of the circle
let step p2r / 360 ;; make step lengths 1/360th of the circumference
crt 1 [ ;; create a single drawing turtle
setxy cx + r cy ;; move it to the highlight patch + the radius
pd ;; put the pen down
set heading 0 ;; make it face along the tangent
while [ p2r > 0 ] [ ;; make the turtle continue to move until the circle is drawn
lt 1
fd step
set p2r p2r - step
set color white
]
]
end
And If i use cx 40 and cy 20 the circle is not from y -20 to y 20, but is only from y 0 to y 20.
How Can I do that?

Answer 1

Maybe a procedure with arguments would be better for this, something like:
to setup
ca
resize-world -20 20 -20 20
draw-semi-circle 0 0 15 45 blue
draw-semi-circle 5 5 5 270 red
draw-semi-circle -10 -10 8 135 green
reset-ticks
end
to draw-semi-circle [ x y r a col ]
; Give arguments for x, y, radius, and angle of the semicircle
let half-p ( pi * r )
let step half-p / 180
ask patch x y [
set pcolor col
]
crt 1 [
setxy x y
set heading a
lt 90
set color col
back r
pd
fd 2 * r
rt 90
while [ half-p > step ] [
rt 1
fd step
set half-p half-p - step
]
]
end
To get an output like: