add arc_path

src/arc_path.scad

@@ -0,0 +1,39 @@
+/**
+* arc_shape.scad
+*
+* Creates an arc. You can pass a 2 element vector to define the central angle. 
+* Its $fa, $fs and $fn parameters are consistent with the circle module.
+* It depends on the circular_sector module so you have to include circular_sector.scad.
+* 
+* @copyright Justin Lin, 2017
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib-arc_shape.html
+*
+**/ 
+
+include <__private__/__frags.scad>;
+include <__private__/__is_vector.scad>;
+include <__private__/__ra_to_xy.scad>;
+
+function __edge_r_begin(orig_r, a, a_step, m) =
+    let(leng = orig_r * cos(a_step / 2))
+    leng / cos((m - 0.5) * a_step - a);
+
+function __edge_r_end(orig_r, a, a_step, n) =      
+    let(leng = orig_r * cos(a_step / 2))    
+    leng / cos((n + 0.5) * a_step - a);
+
+function arc_path(radius, angle) =
+    let(
+        frags = __frags(radius),
+        a_step = 360 / frags,
+        angles = __is_vector(angle) ? angle : [0, angle],
+        m = floor(angles[0] / a_step) + 1,
+        n = floor(angles[1] / a_step),
+        points = concat([__ra_to_xy(__edge_r_begin(radius, angles[0], a_step, m), angles[0])],
+            m > n ? [] : [
+                for(i = [m:n]) 
+                    __ra_to_xy(radius, a_step * i)
+            ])
+    ) points;