add doc

README.md

@@ -243,7 +243,7 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 
 - [vx_bezier](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_bezier.html)
 - [vx_curve](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_curve.html)
-- vx_contour
+- [vx_contour](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_contour.html)
 
 ### Maze
 

docs/lib2x-vx_contour.md

@@ -0,0 +1,35 @@
+# vx_contour
+
+Given a list of points that form a closed area, `vx_contour` returns the contour which encircles the area.
+
+## Parameters
+
+- `points` : A list of `[x, y]` points.
+- `sorted` : Default to `false`. If your points is sorted by x y, setting it to `true` will accelerate the calculation speed.
+
+## Examples
+
+    use <voxel/vx_ascii.scad>;
+    use <voxel/vx_contour.scad>;
+
+    t = "dotSCAD";
+
+    color("white")
+    linear_extrude(2)
+    for(i = [0:len(t) - 1]) {
+        translate([i * 8, 0]) 
+            for(pt = vx_ascii(t[i])) {
+                translate(pt)
+                    square(1, center = true);
+            }
+    }
+
+    color("black")
+    linear_extrude(1)
+    for(i = [0:len(t) - 1]) {
+        pts = vx_ascii(t[i]);
+        translate([i * 8, 0]) 
+        polygon(vx_contour(pts));
+    }
+
+![vx_curve](images/lib2x-vx_contour-1.JPG)

src/voxel/vx_contour.scad

@@ -1,3 +1,13 @@
+/**
+* vx_contour.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_contour.html
+*
+**/ 
+
 use <_impl/_vx_contour_impl.scad>;
 use <util/sort.scad>;