OpenSCAD prefers clockwise

docs/lib-polysections.md

@@ -12,28 +12,30 @@ Looks like extruding along the path? Yes, it can perform the task; however, it's
 
 You can also view it as a better polyline3d module if you want. If you have only the points of a path, using `polyline3d` or `hull_polyline3d` is a simple solution. If you know the cross-sections along a path, you can use `polysections` to do more. 
 
-When using this module, you should use points to represent each cross-section. 
+When using this module, you should use points to represent each cross-section. The points of your 2D shape should have count-clockwise indexes. For example:
 
-If your 2D shape is not solid, indexes of triangles are required. This module has a built-in index vector suitable for one type of hollow shapes. For example, if you have a cross-section such as:
+![polysections](images/lib-polysections-10.JPG)
+
+If your 2D shape is hollow, set the `triangles` parameter to `"HOLLOW"` and index the points as the following:
 
 ![polysections](images/lib-polysections-5.JPG)
 
-When `triangles` is `"HOLLOW"`, the above shape will be cut into triangles such as:
+You can cut triangles by yourself. For example, the above shape can be cut into triangles such as:
 
 ![polysections](images/lib-polysections-6.JPG)
 
-You can cut triangles by yourself, for example, the indexes of the above triangles is:
+The indexes of the above triangles is:
 
     [
-        [0, 3, 4],
-        [0, 4, 1],
-        [1, 4, 5],
-        [1, 5, 2],
-        [2, 5, 3],
-        [2, 3, 0]
+        [0, 4, 3],
+        [0, 1, 4],
+        [1, 5, 4],
+        [1, 2, 5],
+        [2, 3, 5],
+        [2, 0, 3]
     ]
 
-Triangles may be defined in any order.
+In this module, triangles may be defined in any order. Of course, [following the preference of OpenSCAD](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#polyhedron) is ok.
 
 ## Parameters
 
@@ -44,24 +46,24 @@ Triangles may be defined in any order.
 
 	include <rotate_p.scad>;
 	include <polysections.scad>;
-	
+
 	section1 = [
-	    [10, 0, 0],
-	    [15, 10, 0],
-	    [18, 9, 0],
-	    [20, 0, 0]
+		[20, 0, 0],
+		[18, 9, 0],
+		[15, 10, 0],
+		[10, 0, 0]
 	];
-	
+
 	// spin section1
 	sections = [
-	    for(i = [0:55]) 
-	        [
-	            for(p = section1)
-	                let(pt = rotate_p(p, [90, 0, -10 * i]))
-	                [pt[0], pt[1] , pt[2] + i]
-	        ]
+		for(i = [0:55]) 
+			[
+				for(p = section1)
+					let(pt = rotate_p(p, [90, 0, 10 * i]))
+					[pt[0], pt[1] , pt[2] + i]
+			]
 	];
-	    
+
 	polysections(sections);
 
 ![polysections](images/lib-polysections-7.JPG)
@@ -71,15 +73,15 @@ Triangles may be defined in any order.
 	
 	section1 = [
 	    // outer
-	    [10, 0, 0],
-	    [15, 10, 0],
-	    [18, 9, 0],
-	    [20, 0, 0],
+		[20, 0, 0],
+		[18, 9, 0],
+		[15, 10, 0],
+		[10, 0, 0],
 	    // inner
-	    [12, 2, 0],
-	    [15, 7, 0],
-	    [17, 7, 0],
-	    [18, 2, 0]
+        [18, 2, 0],
+        [17, 7, 0],
+        [15, 7, 0],
+	    [12, 2, 0]
 	];
 	
 	// spin section1
@@ -87,7 +89,7 @@ Triangles may be defined in any order.
 	    for(i = [0:55]) 
 	        [
 	            for(p = section1)
-	                let(pt = rotate_p(p, [90, 0, -10 * i]))
+	                let(pt = rotate_p(p, [90, 0, 10 * i]))
 	                [pt[0], pt[1] , pt[2] + i]
 	        ]
 	];
@@ -101,13 +103,13 @@ Triangles may be defined in any order.
 	
 	section1 = [
 	    // outer
-	    [10, 0, 0],
+        [30, 0, 0],
 	    [15, 10, 0],
-	    [30, 0, 0],
+	    [10, 0, 0],
 	    // inner
-	    [12, 1, 0],
+	    [26, 1, 0],
 	    [15, 8, 0],
-	    [26, 1, 0],        
+	    [12, 1, 0],        
 	];
 	
 	// spin section1
@@ -115,7 +117,7 @@ Triangles may be defined in any order.
 	    for(i = [0:55]) 
 	        [
 	            for(p = section1)
-	                let(pt = rotate_p(p, [90, 0, -10 * i]))
+	                let(pt = rotate_p(p, [90, 0, 10 * i]))
 	                [pt[0], pt[1] , pt[2] + i]
 	        ]
 	];
@@ -123,13 +125,13 @@ Triangles may be defined in any order.
 	polysections(
 	   sections = sections, 
 	   triangles = [
-	        [0, 3, 4],
-	        [0, 4, 1],
-	        [1, 4, 5],
-	        [1, 5, 2],
-	        [2, 5, 3],
-	        [2, 3, 0]
-	    ]
+            [0, 3, 1],
+            [1, 3, 4],
+            [1, 4, 2],
+            [2, 4, 5],
+            [2, 5, 0],
+            [0, 5, 3]
+        ]
 	);
 
 ![polysections](images/lib-polysections-9.JPG)

src/polysections.scad

@@ -12,6 +12,13 @@
 **/
 
 module polysections(sections, triangles = "SOLID") {
+    function reverse(vt) = 
+        let(leng = len(vt))
+        [
+            for(i = [0:leng - 1])
+                vt[leng - 1 - i]
+        ];
+
     function side_indexes(sects, begin_idx = 0) = 
         let(       
             leng_sects = len(sects),
@@ -39,13 +46,14 @@ module polysections(sections, triangles = "SOLID") {
         );
 
     module solid_sections(sects) {
+        leng_sects = len(sects);
         leng_pts_sect = len(sects[0]);
   
         first_idxes = [for(i = [0:leng_pts_sect - 1]) leng_pts_sect - 1 - i];  
 
         last_idxes = [
             for(i = [0:leng_pts_sect - 1]) 
-                i + leng_pts_sect * (len(sects) - 1)
+                i + leng_pts_sect * (leng_sects - 1)
         ];    
 
         v_pts = [
@@ -75,17 +83,28 @@ module polysections(sections, triangles = "SOLID") {
                     ]
             ]; 
 
-        function end_idxes(begin_idx) = 
+        function first_idxes() = 
             [
                 for(i =  [0:half_leng_sect - 1]) 
                     [
-                        begin_idx + i, 
-                        begin_idx + (i + 1) % half_leng_sect, 
-                        begin_idx + (i + 1) % half_leng_sect + half_leng_v_pts, 
-                        begin_idx + i + half_leng_v_pts
-                    ]
+                       i,
+                       i + half_leng_v_pts,
+                       (i + 1) % half_leng_sect + half_leng_v_pts, 
+                       (i + 1) % half_leng_sect
+                    ] 
             ];
 
+        function last_idxes(begin_idx) = 
+            [
+                for(i =  [0:half_leng_sect - 1]) 
+                    [
+                       begin_idx + i,
+                       begin_idx + (i + 1) % half_leng_sect,
+                       begin_idx + (i + 1) % half_leng_sect + half_leng_v_pts,
+                       begin_idx + i + half_leng_v_pts
+                    ]     
+            ];            
+
         outer_sects = strip_sects(0, half_leng_sect - 1);
         inner_sects = strip_sects(half_leng_sect, leng_sect - 1);
 
@@ -100,10 +119,14 @@ module polysections(sections, triangles = "SOLID") {
         inner_v_pts = to_v_pts(inner_sects);
 
         outer_idxes = side_indexes(outer_sects);
-        inner_idxes = side_indexes(inner_sects, half_leng_v_pts);
-        first_idxes = end_idxes(0);
-        last_idxes = end_idxes(half_leng_v_pts - half_leng_sect);
+        inner_idxes = [ 
+            for(idxes = side_indexes(inner_sects, half_leng_v_pts))
+                reverse(idxes)
+        ];
 
+        first_idxes = first_idxes();
+        last_idxes = last_idxes(half_leng_v_pts - half_leng_sect);
+        
         polyhedron(
               concat(outer_v_pts, inner_v_pts),
               concat(first_idxes, outer_idxes, inner_idxes, last_idxes)
@@ -116,8 +139,8 @@ module polysections(sections, triangles = "SOLID") {
                 points = concat(tri1, tri2),
                 faces = [
                     [0, 1, 2], 
-                    [3, 4, 5], 
-                    [0, 1, 4], [1, 2, 5], [2, 0, 3], 
+                    [3, 5, 4], 
+                    [0, 4, 1], [1, 5, 2], [2, 3, 0], 
                     [0, 3, 4], [1, 4, 5], [2, 5, 3]
                 ]
             );