add doc

README.md

@@ -242,7 +242,7 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 ### Voxel
 
 - [vx_bezier](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_bezier.html)
-- vx_curve
+- [vx_curve](https://openhome.cc/eGossip/OpenSCAD/lib2x-vx_curve.html)
 - vx_contour
 
 ### Maze

docs/lib2x-vx_curve.md

@@ -0,0 +1,35 @@
+# vx_curve
+
+Draws a voxel-by-voxel curve from control points. The curve is drawn only from the 2nd control point to the second-last control point. It's a voxel version of [curve](https://openhome.cc/eGossip/OpenSCAD/lib2x-curve.html). 
+
+## Parameters
+
+- `points` : A list of `[x, y]` or `[x, y, z]` control points.
+- `tightness` : You can view it as the curve tigntness if you provide a value between 0.0 and 1.0. The default value is 0.0. See [curve](https://openhome.cc/eGossip/OpenSCAD/lib2x-curve.html) for details.
+
+## Examples
+
+    use <voxel/vx_curve.scad>;
+    use <hull_polyline3d.scad>;
+
+    pts = [
+        [28, 2, 1],
+        [15, 8, -10],
+        [2, 14, 5],
+        [28, 14, 2],
+        [15, 21, 9],
+        [2, 28, 0]
+    ];
+
+    for(pt = vx_curve(pts)) {
+    translate(pt)
+            cube(1);
+    }
+
+    #for(pt = pts) {
+        translate(pt)
+            sphere(1);
+    }
+    #hull_polyline3d(pts, .1);  
+
+![vx_curve](images/lib2x-vx_curve-1.JPG)