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Created March 18, 2014 15:48
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 // points = number of points (minimum 3) // outer = radius to outer points // inner = radius to inner points module Star(points, outer, inner) { // polar to cartesian: radius/angle to x/y function x(r, a) = r * cos(a); function y(r, a) = r * sin(a); // angular width of each pie slice of the star increment = 360/points; union() { for (p = [0 : points-1]) { // outer is outer point p // inner is inner point following p // next is next outer point following p assign( x_outer = x(outer, increment * p), y_outer = y(outer, increment * p), x_inner = x(inner, (increment * p) + (increment/2)), y_inner = y(inner, (increment * p) + (increment/2)), x_next = x(outer, increment * (p+1)), y_next = y(outer, increment * (p+1))) { polygon(points = [[x_outer, y_outer], [x_inner, y_inner], [x_next, y_next], [0, 0]], paths = [[0, 1, 2, 3]]); } } } }

### sbliven commented Jun 14, 2020

Thanks! For regular pentagrams I defined:

``````module pentagram(outer) {
inner = outer*sqrt(3.5-1.5*sqrt(5));
Star(5,outer, inner);
}
``````

### louigi600 commented Aug 17, 2022

Assign is going to be deprecated so while I was at it I rewrote the module a little simpler : (it can now take either radii or diameters)

``````module star(p, d1=0, d2=0, r1=0, r2=0)
{ R1= r1!=0 ? r1: d1/2;
D1= d1!=0 ? d1: 2*r1;
R2= r2!=0 ? r2: d2/2;
D2= d2!=0 ? d2: 2*r2;

union()
{ for(i=[0:p-1])
{ i1=[cos(i*360/p - 180/p)*R1,sin(i*360/p - 180/p )*R1]; //first inner point
i2=[cos(i*360/p + 180/p)*R1,sin(i*360/p + 180/p)*R1]; //second inner point
i3=[cos(i*360/p + 180)*R1,sin(i*360/p + 180)*R1];      //third inner point
o=[cos(i*360/p)*R2,sin(i*360/p)*R2];                           //outer point
polygon([i1,o,i2,i3],[[0,1,2,3]]);
}
}
}
``````

### zorgoz commented Nov 28, 2022

Have you tried it with 3? Won't work - you get a triangle. It won't behave correctly when increasing the number of tips.
This is way simpler:

``````module Star(p=5, r1=4, r2=10) {
s = [for(i=[0:p*2])
[
(i % 2 == 0 ? r1 : r2)*cos(180*i/p),
(i % 2 == 0 ? r1 : r2)*sin(180*i/p)
]
];

polygon(s);
}
``````