add convex_hull

src/experimental/_impl/_convex_hull_impl.scad

@@ -0,0 +1,46 @@
+use <util/slice.scad>;
+
+// oa->ob ct_clk : greater than 0
+function _dir(o, a, b) =
+    let(
+        ox = o[0],
+        oy = o[1],
+        ax = a[0],
+        ay = a[1],
+        bx = b[0],
+        by = b[1]
+    )
+    (ax - ox) * (by - oy) - (ay - oy) * (bx - ox);
+
+function _lower_m(chain, p, m) = 
+    (m >= 2 && _dir(chain[m - 2], chain[m - 1], p) <= 0) ? _lower_m(chain, p, m - 1) : m;
+
+function lower_chain(points, leng, chain, m, i) =
+    i == leng ? chain : 
+        let(
+            current_m = _lower_m(chain, points[i], m)
+        )
+        lower_chain(
+            points,
+            leng,
+            concat(slice(chain, 0, current_m), [points[i]]),
+            current_m + 1,
+            i + 1
+        );
+            
+function _upper_m(chain, p, m, t) =
+    (m >= t && _dir(chain[m - 2], chain[m - 1], p) <= 0) ?
+        _upper_m(chain, p, m - 1, t) : m;
+        
+function _upper_chain(points, chain, m, t, i) =
+    i < 0 ? chain :
+        let(
+            current_m = _upper_m(chain, points[i], m, t)
+        )
+        _upper_chain(
+            points,
+            concat(slice(chain, 0, current_m), [points[i]]),
+            current_m + 1,
+            t,
+            i - 1
+        );

src/experimental/convex_hull.scad

@@ -0,0 +1,12 @@
+use <experimental/_impl/_convex_hull_impl.scad>;
+use <util/sort.scad>;
+
+function convex_hull(points) = 
+    let(
+        sorted = sort(points, by = "x"),
+        leng = len(sorted),
+        lwr_ch = lower_chain(sorted, leng, [], 0, 0),
+        leng_lwr_ch = len(lwr_ch),
+        chain = _upper_chain(sorted, lwr_ch, leng_lwr_ch, leng_lwr_ch + 1, leng - 2)
+    )
+    [for(i = [0:len(chain) - 2]) chain[i]];