add hollow_out_torus_knot

examples/hollow_out/hollow_torus_knot.scad

@@ -0,0 +1,76 @@
+use <torus_knot.scad>;
+use <cross_sections.scad>;
+use <util/rand.scad>;
+use <circle_path.scad>;
+use <shape_pentagram.scad>;
+use <hull_polyline3d.scad>;
+use <experimental/tri_bisectors.scad>;
+
+p = 2;
+q = 3;
+phi_step = 0.075;
+thickness = .1;
+shape = shape_pentagram(.5); // circle_path(radius = .5, $fn = 12);
+
+hollow_out_torus_knot(shape, p, q, phi_step, thickness, $fn = 4);
+
+module hollow_out_torus_knot(shape, p, q, phi_step, thickness) {
+    function angy_angz(p1, p2) = 
+        let(
+            dx = p2[0] - p1[0],
+            dy = p2[1] - p1[1],
+            dz = p2[2] - p1[2],
+            ya = atan2(dz, sqrt(dx * dx + dy * dy)),
+            za = atan2(dy, dx)
+        ) [ya, za];
+
+    function sects_by_path(shape, path) =
+        let(
+            lines = [
+                for(i = [0:len(path) - 2])
+                [path[i], path[i + 1]]
+            ],
+            angles = [
+                for(line = lines)
+                let(a = angy_angz(line[0], line[1]))
+                [0, 90 - a[0], a[1]]
+            ]
+        )
+       cross_sections(shape, path, concat([angles[0]], angles));
+
+    function rects(sects) = 
+        let(
+            sects_leng = len(sects),
+            shape_pt_leng = len(sects[0])
+        )
+        [
+            for(i = [0:sects_leng - 1])
+                let(
+                    sect1 = sects[i],
+                    sect2 = sects[(i + 1) % sects_leng]
+                )
+                for(j = [0:shape_pt_leng - 1])
+                    let(k = (j + 1) % shape_pt_leng)
+                    [sect1[j], sect1[k], sect2[k], sect2[j]]
+        ];
+        
+    function rand_tris(rect) =
+        let(
+            i = ceil(rand() * 10) % 2
+        )
+        i == 0 ?
+            [[rect[0], rect[1], rect[2]], [rect[0], rect[2], rect[3]]] :
+            [[rect[1], rect[2], rect[3]], [rect[1], rect[3], rect[0]]];        
+    
+    
+    pts = torus_knot(p, q, phi_step);
+    sects = sects_by_path(shape, pts);
+
+    for(rect = rects(sects)) {
+        for(tri = rand_tris(rect)) {
+            for(line = tri_bisectors(tri)) {
+                hull_polyline3d(line, thickness = thickness);
+            }
+        }
+    }
+}