add doc

README.md

@@ -149,7 +149,7 @@ See [examples](examples).
     - [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](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_circle.html)
-	- ptf/ptf_bend
+	- [ptf/ptf_bend](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_bend.html)
 	- ptf/ptf_ring
 	- ptf/ptf_sphere
 	- ptf/ptf_torus

docs/lib2x-ptf_bend.md

@@ -0,0 +1,32 @@
+# ptf_bend
+
+Transforms a point inside a rectangle to a point of an arc.
+
+**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 arc.
+- `angle` : The central angle of the arc.
+
+## Examples
+
+    use <pixel/px_ascii.scad>;
+    use <ptf/ptf_bend.scad>;
+
+    t = "dotSCAD";
+    size = [len(t) * 8, 8];
+    radius = 20;
+    angle = 180;
+
+    for(i = [0:len(t) - 1]) {
+        for(pt = px_ascii(t[i], invert = true)) {
+            bended = ptf_bend(size, pt + [i * 8, 0], radius, angle);
+            translate(bended)
+                sphere(0.5, $fn = 24);
+        }
+    }
+
+![ptf_bend](images/lib2x-ptf_bend-1.JPG)

src/ptf/ptf_bend.scad

@@ -1,9 +1,12 @@
-/*
-    size: The size of the rectangle which can contain the point.
-    point: A point in the rectangle.
-    radius: The radius of the arc after being bent
-    angle: The central angle of the arc.
-*/
+/**
+* ptf_bend.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_bend.html
+*
+**/ 
 
 function ptf_bend(size, point, radius, angle) = 
     let(