added helix_extrude.scad

src/helix_extrude.scad

@@ -0,0 +1,38 @@
+/**
+* helix_extrude.scad
+*
+* Extrudes a 2D shape along a helix path.
+*
+* @copyright Justin Lin, 2017
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib-helix_extrude.html
+*
+**/
+
+module helix_extrude(shape_pts, radius, levels, level_dist, vt_dir = "SPI_UP", rt_dir = "CT_CLK", twist = 0, scale = 1.0, triangles = "RADIAL") {
+    frags = $fn > 0 ? 
+            ($fn >= 3 ? $fn : 3) : 
+            max(min(360 / $fa, radius * 6.28318 / $fs), 5);
+
+    v_dir = vt_dir == "SPI_UP" ? 1 : -1;
+    r_dir = rt_dir == "CT_CLK" ? 1 : -1;
+            
+    angle_step = 360 / frags * r_dir;
+    initial_angle = atan2(level_dist / frags, 6.28318 * radius / frags) * v_dir * r_dir;
+
+    path_points = helix(
+        radius = radius, 
+        levels = levels, 
+        level_dist = level_dist, 
+        vt_dir = vt_dir, 
+        rt_dir = rt_dir
+    );
+
+    angles = [for(i = [0:len(path_points) - 1]) [90 + initial_angle, 0, angle_step * i]];
+
+    polysections(
+        cross_sections(shape_pts, path_points, angles, twist, scale),
+        triangles = triangles
+    );
+}