sub arc(optional float r,a,b,s)
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float ar,br,c
if not r then r=1.0
if a=0. and b=0. then b=360
if not s then s=5.0
if s<0. then s=-s
if b<a then c=a : a=b : b=c 'swap
glBegin GL_LINE_STRIP
do
ar=rad(a)
br=rad(b)
glVertex2f r*cos(ar),r*sin(ar)
a+=s
if a>=b
glVertex2f r*cos(br),r*sin(br)
exit do
end if
end do
glEnd
end sub