add doc

README.md

@@ -148,7 +148,7 @@ See [examples](examples).
     - [ptf/ptf_rotate](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_rotate.html)
     - [ptf/ptf_x_twist](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_x_twist.html)
 	- [ptf/ptf_y_twist](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_y_twist.html)
-	- ptf/ptf_circle
+	- [ptf/ptf_circle](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_circle.html)
 	- ptf/ptf_bend
 	- ptf/ptf_ring
 	- ptf/ptf_sphere

docs/lib2x-ptf_circle.md

@@ -0,0 +1,41 @@
+# ptf_circle
+
+Transform a point inside a rectangle to a point inside a circle. You can use it to create something such as a [noisy circle maze](https://github.com/JustinSDK/dotSCAD/blob/master/examples/maze/noisy_circle_maze.scad).
+
+![ptf_circle](images/lib2x-ptf_circle-1.JPG)
+
+**Since:** 2.3.
+
+## Parameters
+
+- `size` : 2 value array `[x, y]`, rectangle with dimensions `x` and `y`.
+- `point` : The point to be transformed.
+
+## Examples
+
+    use <hull_polyline3d.scad>;
+    use <ptf/ptf_circle.scad>;
+
+    size = [10, 10];
+
+    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_circle(size, p)];
+        hull_polyline3d(twisted, thickness = .1);
+    }
+
+    for(line = columns) {
+        twisted = [for(p = line) ptf_circle(size, p)];
+        hull_polyline3d(twisted, thickness = .1);
+    }
+
+![ptf_circle](images/lib2x-ptf_circle-2.JPG)

src/ptf/ptf_circle.scad

@@ -1,3 +1,13 @@
+/**
+* ptf_circle.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_circle.html
+*
+**/ 
+
 function ptf_circle(size, point) =
     let(
         p_offset = -size / 2,