add doc

README.md

@@ -152,8 +152,8 @@ See [examples](examples).
 	- [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](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_sphere.html)
-	- ptf/ptf_torus
-
+	- [ptf/ptf_torus](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_torus.html)
+	
 ----
 
 - Turtle

docs/lib2x-ptf_torus.md

@@ -0,0 +1,47 @@
+# ptf_torus
+
+Transforms a point inside a rectangle to a point of a torus. It can create things such as [torus maze](https://github.com/JustinSDK/dotSCAD/blob/master/examples/maze/torus_maze.scad).
+
+![ptf_torus](images/lib2x-ptf_torus-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` : Torus `[R, r]`.
+- `angle` : Torus `[A, a]`.
+- `twist` : The number of degrees of through which the rectangle is twisted.
+
+## Examples
+
+    use <hull_polyline3d.scad>;
+    use <ptf/ptf_torus.scad>;
+
+    size = [20, 10];
+    radius = [10, 5];
+    angle = [180, 180];
+    twist = 90;
+
+    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_torus(size, p, radius, angle, twist)];
+        hull_polyline3d(twisted, thickness = .5);
+    }
+
+    for(line = columns) {
+        twisted = [for(p = line) ptf_torus(size, p, radius, angle, twist)];
+        hull_polyline3d(twisted, thickness = .5);
+    }
+
+![ptf_torus](images/lib2x-ptf_torus-2.JPG)