add vx_curve

src/voxel/vx_curve.scad

@@ -0,0 +1,30 @@
+use <../util/sort.scad>;
+use <../util/dedup.scad>;
+use <vx_bezier.scad>;
+
+function _vx_catmull_rom_spline_4pts(points, tightness) = 
+    let(
+        p1x_0tightness = (points[2] - points[0]) / 4 + points[1],
+        v_p1x = points[1] - p1x_0tightness,
+        p1x = p1x_0tightness + v_p1x * tightness,
+        p2x_0tightness = (points[1] - points[3]) / 4 + points[2],
+        v_p2x = points[2] - p2x_0tightness,
+        p2x = p2x_0tightness + v_p2x * tightness
+    )
+    vx_bezier(points[1], p1x, p2x, points[2]);
+
+function vx_curve(points, tightness = 0) = 
+    let(
+        leng = len(points),
+        pts = concat(
+            [
+                for(i = [0:leng - 4])
+                    let(
+                        pts = _vx_catmull_rom_spline_4pts([for(j = [i:i + 3]) points[j]], tightness)
+                    )
+                    for(i = [0:len(pts) - 2]) pts[i]    
+            ],
+            [points[leng - 2]]
+        )
+    )
+    dedup(sort(pts, by = "vt"), sorted = true);