add _vertex_normals

src/__comm__/_vertex_normals.scad

@@ -0,0 +1,44 @@
+
+use <../util/slice.scad>;
+use <../util/sort.scad>;
+use <../util/find_index.scad>;
+use <../util/sum.scad>;
+
+ascending = function(e1, e2) e1 - e2;
+
+function connected_faces(leng_pts, faces) =
+	let(
+		leng = len(faces),
+		cnt_faces = [for(i = [0:leng_pts - 1]) []]
+	)
+	_connected_faces(faces, leng, leng_pts, cnt_faces);
+	
+function _connected_faces(faces, leng, leng_pts, cnt_faces, i = 0) = 
+	i == leng ? cnt_faces :
+	let(
+		facei = sort(faces[i], by = ascending),
+		n_cnt_faces = [
+		    for(k = [0:leng_pts - 1])
+			find_index(facei, function(e) e == k) != -1 ? concat(cnt_faces[k], [faces[i]]) : cnt_faces[k]
+		]
+	)
+	_connected_faces(faces, leng, leng_pts, n_cnt_faces, i + 1);
+
+function face_normal(points) =
+	let(v = cross(points[2] - points[0], points[1] - points[0])) v / norm(v); 
+	
+function _vertex_normals(points, faces) = 
+    let(
+	    leng_pts = len(points),
+	    cnn_faces = connected_faces(leng_pts, faces)
+	)
+	[
+		for(i = [0:leng_pts - 1])
+		let(
+			face_normals = [
+				for(face = cnn_faces[i])
+					face_normal([for(i = face) points[i]])
+			]
+		)
+		sum(face_normals) / len(face_normals)
+	];