From daaff1322f0ec75bd322302cd95ee8747083216d Mon Sep 17 00:00:00 2001
From: Justin Lin <justin.sdk@gmail.com>
Date: Tue, 13 Sep 2022 14:56:36 +0800
Subject: [PATCH] add tri_concave_hull

---
 src/experimental/tri_concave_hull.scad | 92 ++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 src/experimental/tri_concave_hull.scad

diff --git a/src/experimental/tri_concave_hull.scad b/src/experimental/tri_concave_hull.scad
new file mode 100644
index 00000000..0e961871
--- /dev/null
+++ b/src/experimental/tri_concave_hull.scad
@@ -0,0 +1,92 @@
+use <triangle/tri_delaunay.scad>
+use <triangle/tri_delaunay_indices.scad>
+use <triangle/tri_circumcenter.scad>
+use <util/map/hashmap.scad>
+use <util/map/hashmap_get.scad>
+use <util/map/hashmap_put.scad>
+use <util/map/hashmap_entries.scad>
+use <util/has.scad>
+
+function circumcircle_rr(shape_pts) =
+   let(
+	  center = tri_circumcenter(shape_pts),
+	  v = shape_pts[0] - center
+   )
+   v * v;
+   
+function edge(a, b) = a < b ? [a, b] : [b, a];   
+
+function dist_gt(p1, p2, leng) = let(v = p2 - p1) v * v > leng ^ 2;
+
+function edge_tri(indices_tris, m, i = 0) = 
+    len(indices_tris) == i ? m :
+    let(
+        t_indices = indices_tris[i],
+        
+        edge1 = edge(t_indices[0], t_indices[1]),
+        t_lt1 = hashmap_get(m, edge1),
+        m1 = hashmap_put(m, edge1, is_undef(t_lt1) ? [t_indices] : [each t_lt1, t_indices]),
+        
+        edge2 = edge(t_indices[1], t_indices[2]),
+        t_lt2 = hashmap_get(m1, edge2),
+        m2 = hashmap_put(m1, edge2, is_undef(t_lt2) ? [t_indices] : [each t_lt2, t_indices]),
+        
+        edge3 = edge(t_indices[2], t_indices[0]),
+        t_lt3 = hashmap_get(m2, edge3)
+    )
+    edge_tri(indices_tris, hashmap_put(m2, edge3, is_undef(t_lt3) ? [t_indices] : [each t_lt3, t_indices]), i + 1);
+
+function reduce_tris(indices_tris, dist) = 
+    let(
+        m = edge_tri(indices_tris, hashmap(number_of_buckets = len(indices_tris) / 4)),  
+        entries = hashmap_entries(m), 
+        edges = [
+            for(entry = entries)  
+            if(len(entry[1]) == 1 && dist_gt(points[entry[0][0]], points[entry[0][1]], dist))
+            entry[0]
+        ],
+        reduce_tris = [
+            for(t_indices = indices_tris) 
+            let(
+                edge1 = edge(t_indices[0], t_indices[1]),
+                edge2 = edge(t_indices[1], t_indices[2]),
+                edge3 = edge(t_indices[2], t_indices[0])
+            )
+            if(
+                !has(edges, edge1) && !has(edges, edge2) && !has(edges, edge3)
+            )
+            t_indices
+        ]
+    )
+    len(indices_tris) > len(reduce_tris) ? reduce_tris(reduce_tris, dist) : reduce_tris;
+
+    
+function tri_concave_hull(points, dist, d) = 
+    let(
+        indices_tris = is_undef(d) ? tri_delaunay(points) : tri_delaunay_indices(d)
+    )
+    reduce_tris(indices_tris, dist);
+   
+dist = 30;
+seed = 101;
+points = [for(i = [0:150]) rands(-100, 100, 2, seed_value = seed + i)]; 
+
+d = tri_delaunay(points, ret = "DELAUNAY");
+convex_hull_tris = tri_delaunay_indices(d);
+concave_hull_tris = tri_concave_hull(points, dist, d); 
+
+for(t = concave_hull_tris) {
+    offset(-.2)
+    polygon([for(i = t) points[i]]);
+}
+
+%for(t = convex_hull_tris) {
+    offset(-.2)
+    polygon([for(i = t) points[i]]);
+}
+
+color("red")
+for(p = points) {
+    translate(p)
+    circle(2);
+}