added shape_pie

README.md

@@ -28,8 +28,8 @@ Too many dependencies? Because OpenSCAD doesn't provide namespace management, I
 ## Documentation
 
 - 2D
-    - [pie](https://openhome.cc/eGossip/OpenSCAD/lib-pie.html)
-	- [arc](https://openhome.cc/eGossip/OpenSCAD/lib-arc.html)
+    - [arc](https://openhome.cc/eGossip/OpenSCAD/lib-arc.html)
+	- [pie](https://openhome.cc/eGossip/OpenSCAD/lib-pie.html)
 	- [ellipse](https://openhome.cc/eGossip/OpenSCAD/lib-ellipse.html)
 	- [rounded_square](https://openhome.cc/eGossip/OpenSCAD/lib-rounded_square.html)
 	- [line2d](https://openhome.cc/eGossip/OpenSCAD/lib-line2d.html)
@@ -80,7 +80,8 @@ Too many dependencies? Because OpenSCAD doesn't provide namespace management, I
 	- [sphere_spiral_extrude](https://openhome.cc/eGossip/OpenSCAD/lib-sphere_spiral_extrude.html)
 
 - Shape
-    - [shape_ellipse](https://openhome.cc/eGossip/OpenSCAD/lib-shape_ellipse.html)
+    - [shape_pie](https://openhome.cc/eGossip/OpenSCAD/lib-shape_pie.html)
+	- [shape_ellipse](https://openhome.cc/eGossip/OpenSCAD/lib-shape_ellipse.html)
     - [shape_square](https://openhome.cc/eGossip/OpenSCAD/lib-shape_square.html)
     - [shape_pentagram](https://openhome.cc/eGossip/OpenSCAD/lib-shape_pentagram.html)		
 	

docs/lib-shape_pie.md

@@ -0,0 +1,35 @@
+# shape_pie
+
+Returns shape points and triangle indexes of a pie (circular sector) shape. They can be used with xxx_extrude modules of dotSCAD. The shape points can be also used with the built-in polygon module. 
+
+## Parameters
+
+- `radius` : The radius of the circle.
+- `angles` : A 2 element vector which defines the central angle. The first element of the vector is the beginning angle in degrees, and the second element is the ending angle.
+- `$fa`, `$fs`, `$fn` : Check [the circle module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#circle) for more details.
+
+## Examples
+
+	include <shape_pie.scad>;
+	
+	shape_pts_tris = shape_pie(10, [45, 315], $fn = 24);
+
+![shape_pie](images/lib-shape_pie-1.JPG)
+
+include <shape_pie.scad>;
+include <helix.scad>;
+include <rotate_p.scad>;
+include <cross_sections.scad>;
+include <polysections.scad>;
+include <helix_extrude.scad>;
+
+shape_pts_tris = shape_pie(10, [45, 315], $fn = 8);
+
+helix_extrude(shape_pts_tris[0], 
+    radius = 40, 
+    levels = 5, 
+    level_dist = 20,
+    triangles = shape_pts_tris[1]
+);
+
+![shape_pie](images/lib-shape_pie-2.JPG)

src/shape_pie.scad

@@ -0,0 +1,40 @@
+/**
+* shape_pie.scad
+*
+* Returns shape points and triangle indexes of a pie (circular sector) shape.
+* They can be used with xxx_extrude modules of dotSCAD.
+* The shape points can be also used with the built-in polygon module. 
+*
+* @copyright Justin Lin, 2017
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib-shape_pie.html
+*
+**/
+
+include <__private__/__frags.scad>;
+
+function shape_pie(radius, angles) =
+    let(
+        frags = __frags(radius),
+        a_step = 360 / frags,
+        leng = radius * cos(a_step / 2),
+        m = floor(angles[0] / a_step) + 1,
+        n = floor(angles[1] / a_step),
+        edge_r_begin = leng / cos((m - 0.5) * a_step - angles[0]),
+        edge_r_end = leng / cos((n + 0.5) * a_step - angles[1]),
+        shape_pts = concat(
+            [[0, 0], edge_r_begin * [cos(angles[0]), sin(angles[0])]],
+            [
+                for(i = [m:n]) 
+                    let(a = a_step * i)
+                    radius * [cos(a), sin(a)]
+            ],
+            [edge_r_end * [cos(angles[1]), sin(angles[1])]]
+        ),
+        triangles = [for(i = [1:len(shape_pts) - 2]) [0, i, i + 1]]
+    )
+    [
+        shape_pts,
+        triangles
+    ];