improve keyhole and round_path

box.scad

@@ -196,7 +196,7 @@ module box_part(half_sides, anchor=CENTER, spin, inside=true, auto_anchor=true,
     }
 }
 
-function round_path(path, r) = offset(offset(path,r),-r);
+function round_path(path, r, closed=true) = r==0 ? path : offset(offset(path,r,closed=closed),-r,closed=closed);
 
 function vector_name(v) =
     assert(is_vector(v))

examples/boxsides.scad

@@ -1,8 +1,11 @@
 include <jl_scad/box.scad>
 include <jl_scad/parts.scad>
 
+// $fa = 1;
+// $fn = 48;
+
+$fs=$preview?0.5:0.125;
 $fa = 1;
-$fn = 48;
 
 module my_box(size) {
     // a test box with one piece per side
@@ -46,3 +49,9 @@ my_box(sz)
     //         position(LEFT+FRONT)
     //             cube([15,15,sz.z*0.75],anchor=CENTER,spin=45);
 }
+
+// p = keyhole(r=0);
+// !union() {
+//     region(p);
+//     move_copies(p) color("red",0.5) circle(d=0.2,$fn=8);
+// }

examples/example.scad

@@ -55,5 +55,5 @@ box_shell_base_lid([50,40,20],wall_sides=2,wall_top=1,rim_gap=0,rbot=1,rbot_insi
     // inspect by cutting away corner, we don't use box_part() or box_pos(), but manually position the cube.
     box_half(BOX_ALL) position(CENTER) box_cut("#58c") cube(30,anchor=LEFT+BACK);
 
-    Y(-2) box_part(BOT,BACK) box_cutout(keyhole(),anchor=BACK);
-}
+    Y(-3) box_part(BOT,BACK) box_cutout(keyhole(),anchor=BACK);
+}

parts.scad

@@ -114,14 +114,14 @@ function keyhole_old(d1=3,d2=7,l=5,joint=1) = zrot(180, path_join([
     [[0,l],[0,0]],
 ],joint=joint));
 
-function keyhole(d1=3,d2=6,l,r) =
-    let(r=default(r,d1/2),l=d2)
+function keyhole(d1=3,d2=6,l,r,n=24) =
+    let(r=default(r,d1/2),l=d2,$fn=n) // fn must be even for this to work!
     assert(r<d1)
-    round_path(union([
+    force_path(round_path(union([
         circle(d=d1),
         rect([d1,l],anchor=TOP),
         move([0,-l],circle(d=d2)),
-    ]),r);
+    ]),r));
 
 // p: path of cutout
 // rounding: roundover outer edge