added circle_path

README.md

@@ -24,4 +24,5 @@ I've been using OpenSCAD for years and created some funny things. Some of them i
 	- [bend](https://openhome.cc/eGossip/OpenSCAD/lib-bend.html)
 
 - Path
+    - [circle_path](https://openhome.cc/eGossip/OpenSCAD/lib-circle_path.html)
     - [bezier](https://openhome.cc/eGossip/OpenSCAD/lib-bezier.html)

docs/lib-circle_path.md

@@ -0,0 +1,27 @@
+# circle_path
+
+Sometimes you need all points on the path of a circle. Here's the function. Its `$fa`, `$fs` and `$fn` parameters are consistent with the `circle` module.
+
+## Parameters
+
+- `radius` : The radius of the circle.
+- `$fa`, `$fs`, `$fn` : Check [the circle module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#circle) for more details.
+
+## Examples
+
+	$fn = 24;
+	
+	points = circle_path(radius = 50);
+	polygon(points);
+	
+	leng = len(points);
+	step_angle = 360 / leng;
+	for(i = [0:leng - 1]) {
+	    translate(points[i]) 
+	        rotate([90, 0, 90 + i * step_angle]) 
+	            linear_extrude(1, center = true) 
+	                text("A", valign = "center", halign = "center");
+	}
+
+![circle_path](images/lib-circle_path-1.JPG)
+

src/circle_path.scad

@@ -0,0 +1,23 @@
+/**
+* circle_path.scad
+*
+* Sometimes you need all points on the path of a circle. Here's 
+* the function. Its $fa, $fs and $fn parameters are consistent 
+* with the circle module.
+* 
+* @copyright Justin Lin, 2017
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib-circle_path.html
+*
+**/
+
+function _frags(radius) = $fn > 0 ? 
+        ($fn >= 3 ? $fn : 3) : 
+        max(min(360 / $fa, radius * 2 * 3.14159 / $fs), 5);
+    
+function circle_path(radius) =
+    [
+        for(a = [0 : 360 / _frags(radius) : 360 - 360 / _frags(radius)]) 
+            [radius * cos(a), radius * sin(a)]
+    ];