add hilbert_curve_drawing

examples/turtle/hilbert_curve_drawing.scad

@@ -0,0 +1,29 @@
+use <bezier_smooth.scad>;
+use <hull_polyline3d.scad>;
+use <util/dedup.scad>;
+use <turtle/lsystem3.scad>;
+
+thickness = 0.3;
+corner_r = 0.5;
+
+lines = hilbert_curve();
+hilbert_path = dedup(
+    concat(
+        [for(line = lines) line[0]], 
+        [lines[len(lines) - 1][1]])
+    );
+smoothed_hilbert_path = bezier_smooth(hilbert_path, corner_r);
+
+hull_polyline3d(smoothed_hilbert_path,  thickness = thickness);
+
+function hilbert_curve() = 
+    let(
+        axiom = "A",
+        rules = [
+            ["A", "B-F+CFC+F-D&F^D-F+&&CFC+F+B//"],
+            ["B", "A&F^CFB^F^D^^-F-D^|F^B|FC^F^A//"],
+            ["C", "|D^|F^B-F+C^F^A&&FA&F^C+F+B^F^D//"],
+            ["D", "|CFB-F+B|FA&F^A&&FB-F+B|FC//"]
+        ]
+    )
+    lsystem3(axiom, rules, 2, 90, 1, 0,  [0, 0, 0]);