add footprints3.scad

src/turtle/_impl/_footprints3.scad

@@ -0,0 +1,9 @@
+use <../turtle3d.scad>;
+
+function _footprints3(cmds, t, leng, i = 0) =
+    i == leng ? [] :
+        let(
+            nxt = turtle3d(cmds[i][0], t, cmds[i][1]),
+            pts = _footprints3(cmds, nxt, leng, i + 1)
+        )
+        cmds[i][0] != "forward" && cmds[i][0] != "yu_move" && cmds[i][0] != "zu_move" ? pts : concat([turtle3d("pt", nxt)], pts);

src/turtle/footprints3.scad

@@ -0,0 +1,56 @@
+use <_impl/_footprints3.scad>;
+use <turtle3d.scad>;
+
+/* 
+ cmds: "forward" ("xu_move"), "turn" ("zu_turn"), "roll" ("xu_turn"), "pitch" ("yu_turn"), 
+       "xu_move", "yu_move", "zu_move", "xu_turn", "yu_turn", "turn"
+
+```
+use <hull_polyline3d.scad>;
+use <turtle/footprints3.scad>;
+ 
+function xy_arc_cmds(radius, angle, steps) = 
+    let(
+        fa = angle / steps,
+        ta = fa / 2,
+        leng = sin(ta) * radius * 2
+    )
+    concat(
+        [["turn", ta]],
+        [
+            for(i = [0:steps - 2])
+            each [["forward", leng], ["turn", fa]]
+        ],
+        [["forward", leng], ["turn", ta]]
+    );
+    
+poly = footprints3(
+    concat(
+        [
+            ["forward", 10],
+            ["turn", 90],
+            ["forward", 10] 
+        ], 
+        xy_arc_cmds(5, 180, 12),
+        [
+            ["pitch", -90],
+            ["forward", 10],
+            ["roll", -90]
+        ],
+        xy_arc_cmds(5, 180, 12),
+        [
+            ["forward", 10],
+            ["roll", -90]
+        ]
+    )
+);
+
+hull_polyline3d(poly, thickness = 1);
+```
+*/
+function footprints3(cmds, start = [0, 0, 0]) = 
+    let(
+        t = turtle3d("create", start, [[1, 0, 0], [0, 1, 0], [0, 0, 1]]),
+        leng = len(cmds)
+    )
+    concat([turtle3d("pt", t)], _footprints3(cmds, t, leng));