added cylinder_spiral

README.md

@@ -26,3 +26,4 @@ I've been using OpenSCAD for years and created some funny things. Some of them i
 - Path
     - [circle_path](https://openhome.cc/eGossip/OpenSCAD/lib-circle_path.html)
     - [bezier](https://openhome.cc/eGossip/OpenSCAD/lib-bezier.html)
+    - [cylinder_spiral](https://openhome.cc/eGossip/OpenSCAD/lib-cylinder_spiral.html)

docs/lib-cylinder_spiral.md

@@ -0,0 +1,39 @@
+# cylinder_spiral
+
+Get all points on the path of a spiral around a cylinder. Its `$fa`, `$fs` and `$fn` parameters are consistent with the `cylinder` module. It depends on the `circle_path` module so you have to include circle_path.scad.
+
+## Parameters
+
+- `radius` : The radius of the cylinder.
+- `levels` : The level count is performed every 360 degrees. 
+- `level_dist` : The distance between two vertial points.
+- `vt_dir` : `"CT_CLK"` for counterclockwise. `"CLK"` for clockwise. The default value is `"CT_CLK"`.
+- `rt_dir` : `"SPI_DOWN"` for spiraling down. `"SPI_UP"` for spiraling up. The default value is `"SPI_DOWN"`.
+- `$fa`, `$fs`, `$fn` : Check [the cylinder module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#cylinder) for more details.
+
+
+## Examples
+    
+	include <circle_path.scad>;
+	include <cylinder_spiral.scad>;
+	include <hull_polyline3d.scad>;
+	
+	$fn = 12;
+	
+	points = cylinder_spiral(
+	    radius = 40, 
+	    levels = 10, 
+	    level_dist = 10, 
+	    vt_dir = "SPI_UP", 
+	    rt_dir = "CLK"
+	);
+	
+	for(p = points) {
+	    translate(p) sphere(5);
+	}
+	
+	hull_polyline3d(points, 2);
+
+
+![cylinder_spiral](images/lib-cylinder_spiral-1.JPG)
+