added cross_sections.scad

src/cross_sections.scad

@@ -0,0 +1,36 @@
+/**
+* cross_sections.scad
+*
+* Given a starting cross-section, points and angles along the path, this function
+* will return all cross-sections.
+*
+* @copyright Justin Lin, 2017
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib-cross_sections.html
+*
+**/
+
+function cross_sections(shape_pts, path_pts, angles, twist = 0, scale = 1.0) =
+    let(
+        len_path_pts_minus_one = len(path_pts) - 1,
+        sh_pts = len(shape_pts[0]) == 3 ? shape_pts : [for(p = shape_pts) [p[0], p[1], 0]],
+        pth_pts = len(path_pts[0]) == 3 ? path_pts : [for(p = path_pts) [p[0], p[1], 0]],
+        scale_step_vt = len(scale) == 2 ? 
+            [(scale[0] - 1) / len_path_pts_minus_one, (scale[1] - 1) / len_path_pts_minus_one] :
+            [(scale - 1) / len_path_pts_minus_one, (scale - 1) / len_path_pts_minus_one],
+        scale_step_x = scale_step_vt[0],
+        scale_step_y = scale_step_vt[1],
+        twist_step = twist / len_path_pts_minus_one
+    )
+    [
+        for(i = [0:len_path_pts_minus_one])
+            [
+                for(p = sh_pts) 
+                let(scaled_p = [p[0] * (1 + scale_step_x * i), p[1] * (1 + scale_step_y * i), p[2]])
+                    rotate_p(
+                        rotate_p(scaled_p, twist_step * i)
+                        , angles[i]
+                    ) + pth_pts[i]
+            ]
+    ];