From 5141099b964acfcadece8466828c763aaee369f0 Mon Sep 17 00:00:00 2001
From: Justin Lin <caterpillar@openhome.cc>
Date: Wed, 10 May 2017 22:10:58 +0800
Subject: [PATCH] improved hollow performance

---
 src/polysections.scad | 116 +++++++++++++++++++++++++++---------------
 1 file changed, 75 insertions(+), 41 deletions(-)

diff --git a/src/polysections.scad b/src/polysections.scad
index 34ace6e2..c3d9834e 100644
--- a/src/polysections.scad
+++ b/src/polysections.scad
@@ -12,39 +12,92 @@
 **/
 
 module polysections(sections, triangles = "SOLID") {
+    function side_indexes(sects, begin_idx = 0) = 
+        let(       
+            leng_sects = len(sects),
+            leng_pts_sect = len(sects[0])
+        ) 
+        [
+            for(j = [begin_idx:leng_pts_sect:begin_idx + (leng_sects - 2) * leng_pts_sect])
+                for(i = [0:leng_pts_sect - 1]) 
+                    [
+                        j + i, 
+                        j + (i + 1) % leng_pts_sect, 
+                        j + (i + 1) % leng_pts_sect + leng_pts_sect , 
+                        j + i + leng_pts_sect
+                    ]
+        ];
+
     module solid_sections(sects) {
-        leng_sects = len(sects);
         leng_pts_sect = len(sects[0]);
-        
-        side_idxes = [
-                for(j = [0:leng_pts_sect:(leng_sects - 2) * leng_pts_sect])
-                    for(i = [0:leng_pts_sect - 1]) 
-                        [
-                            j + i, 
-                            j + (i + 1) % leng_pts_sect, 
-                            j + (i + 1) % leng_pts_sect + leng_pts_sect , 
-                            j + i + leng_pts_sect
-                        ]
-             ];
 
         first_idxes = [for(i = [0:leng_pts_sect - 1]) i];   
-        
         last_idxes = [
             for(i = [0:leng_pts_sect - 1]) 
-                i + leng_pts_sect * (leng_sects - 1)
+                i + leng_pts_sect * (len(sects) - 1)
         ];    
         
         v_pts = [
-            for(section = sections) 
-                for(pt = section) 
+            for(sect = sects) 
+                for(pt = sect) 
                     pt
         ];
         
        polyhedron(
            v_pts, 
-           concat([first_idxes], side_idxes, [last_idxes])
+           concat([first_idxes], side_indexes(sects), [last_idxes])
        );    
     }
+
+    module hollow_sections(sects) {
+        leng_sects = len(sects);
+        leng_sect = len(sects[0]);
+        half_leng_sect = leng_sect / 2;
+        half_leng_v_pts = leng_sects * half_leng_sect;
+
+        function strip_sects(begin_idx, end_idx) = 
+            [
+                for(i = [0:leng_sects - 1]) 
+                    [
+                        for(j = [begin_idx:end_idx])
+                            sects[i][j]
+                    ]
+            ]; 
+
+        function end_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);
+
+        function to_v_pts(sects) = 
+             [
+                for(sect = sects) 
+                    for(pt = sect) 
+                        pt
+             ];
+
+        outer_v_pts =  to_v_pts(outer_sects);
+        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);
+
+        polyhedron(
+              concat(outer_v_pts, inner_v_pts),
+              concat(first_idxes, outer_idxes, inner_idxes, last_idxes)
+        ); 
+    }
     
     module triangles_defined_sections() {
         module tri_sections(tri1, tri2) {
@@ -58,30 +111,9 @@ module polysections(sections, triangles = "SOLID") {
                 ]
             );  
         }
-        
-        function hollow_tris() = 
-            let(
-                leng_section = len(sections[0]),
-                inner_i_begin = leng_section / 2,
-                idxes = concat(
-                    [
-                        for(i = [0:inner_i_begin - 1]) 
-                            let(n = inner_i_begin + i + 1)
-                            [i, inner_i_begin + i, n % inner_i_begin + inner_i_begin]
-                    ],
-                    [
-                        for(i = [0:inner_i_begin - 1]) 
-                            let(n = inner_i_begin + i + 1)
-                            [i, i + 1, n % leng_section]
-                    ]
-                )
-            ) idxes; 
-
-        function tris() =
-            triangles == "HOLLOW" ? hollow_tris() : triangles;
 
         module two_sections(section1, section2) {
-            for(idx = tris()) {
+            for(idx = triangles) {
                 // hull is for preventing from WARNING: Object may not be a valid 2-manifold
                 hull() tri_sections(
                     [
@@ -106,10 +138,12 @@ module polysections(sections, triangles = "SOLID") {
         }
     }
     
-    //
     if(triangles == "SOLID") {
         solid_sections(sections);
-    } else {
+    } else if(triangles == "HOLLOW") {
+        hollow_sections(sections);
+    }
+    else {
         triangles_defined_sections();
     }
 }
\ No newline at end of file