add doc

README.md

@@ -151,7 +151,7 @@ See [examples](examples).
 	- [ptf/ptf_circle](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_circle.html)
 	- [ptf/ptf_bend](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_bend.html)
 	- [ptf/ptf_ring](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_ring.html)
-	- ptf/ptf_sphere
+	- [ptf/ptf_sphere]https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_sphere.html)
 	- ptf/ptf_torus
 
 ----

docs/lib2x-ptf_sphere.md

@@ -0,0 +1,45 @@
+# ptf_sphere
+
+Transforms a point inside a rectangle to a point of a sphere. It can create things such as [sphere maze](https://github.com/JustinSDK/dotSCAD/blob/master/examples/maze/sphere_maze.scad).
+
+![ptf_sphere](images/lib2x-ptf_sphere-1.JPG)
+
+**Since:** 2.3
+
+## Parameters
+
+- `size` : 2 value array `[x, y]`, rectangle with dimensions `x` and `y`.
+- `point` : The point to be transformed.
+- `radius` : The radius of the sphere.
+- `angle` : [za, xa] mapping angles.
+
+## Examples
+
+    use <hull_polyline3d.scad>;
+    use <ptf/ptf_sphere.scad>;
+
+    size = [20, 10];
+    radius = 5;
+    angle = [180, 270];
+
+    rows = [
+        for(y = [0:size[1]])
+            [for(x = [0:size[0]]) [x, y]]
+    ];
+
+    columns = [
+        for(x = [0:size[0]])
+            [for(y = [0:size[1]]) [x, y]]
+    ];
+
+    for(line = rows) {
+        twisted = [for(p = line) ptf_sphere(size, p, radius, angle)];
+        hull_polyline3d(twisted, thickness = .5);
+    }
+
+    for(line = columns) {
+        twisted = [for(p = line) ptf_sphere(size, p, radius, angle)];
+        hull_polyline3d(twisted, thickness = .5);
+    }
+
+![ptf_sphere](images/lib2x-ptf_sphere-2.JPG)

src/ptf/ptf_sphere.scad

@@ -1,11 +1,15 @@
+/**
+* ptf_sphere.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_sphere.html
+*
+**/ 
+
 use <ptf/ptf_rotate.scad>;
 
-/*
-    size: The size of the rectangle mapping to a sphere.
-    point: A point in the rectangle.
-    radius: sphere radius.
-    angle: [za, xa] mapping angles.
-*/
 function ptf_sphere(size, point, radius, angle = [180, 360]) =
     let(
         x = point[0],