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graphics ! graphics clear .8,.8,.8 ! draw color 0,0,0
get screen size sw,sh ! xc=sw/2 ! yc=sh/2
option angle degrees
draw size 2 ! R=300 ! da=15
for alfa=0 to 360-da step da
R=50+.6*alfa
xo=xc+8*cos(alfa) ! yo=yc-8*sin(alfa)
xe=xc+R*cos(alfa) ! ye=yc-R*sin(alfa)
draw_arrow(xo,yo,xe,ye)
next alfa
end
'*** draw an arrow from xo,yo to xe,ye ***
' current draw color and draw size are used
'
def draw_arrow(xo,yo,xe,ye)
dim x(6),y(6)
dx=xe-xo ! dy=ye-yo ! L=sqrt(dx^2+dy^2)
a=min(30,0.15*L) ! b=0.2*a ! sina=dy/L ! cosa=dx/L
x(1)=0 ! x(2)=L ! x(3)=L-a ! x(4)=L-a ! x(5)=L-a
y(1)=0 ! y(2)=0 ! y(3)=-b ! y(4)=0 ! y(5)=b
for i=1 to 5
xx=x(i) ! yy=y(i)
x(i)=xo+cosa*xx-sina*yy
y(i)=yo+(sina*xx+cosa*yy)
next i
draw line x(1),y(1) to x(4),y(4)
draw tri x(2),y(2),x(3),y(3),x(5),y(5)
end def