More files for convex_hull

xs/src/Geometry.cpp

@@ -0,0 +1,46 @@
+#include "Geometry.hpp"
+#include <algorithm>
+
+namespace Slic3r {
+
+static bool
+sort_points (Point a, Point b)
+{
+    return (a.x < b.x) || (a.x == b.x && a.y < b.y);
+}
+
+void
+convex_hull(Points points, Polygon &hull)
+{
+    assert(points.size() >= 2);
+    // sort input points
+    std::sort(points.begin(), points.end(), sort_points);
+    
+    typedef const Point* PointPtr;
+    PointPtr* out_hull = (PointPtr*)malloc(points.size()*2*sizeof(PointPtr));
+    
+    /* lower hull */
+    size_t k = 0;
+    for (Points::const_iterator it = points.begin(); it != points.end(); ++it) {
+        while (k >= 2 && it->ccw(out_hull[k-2], out_hull[k-1]) <= 0) --k;
+        Point pz = *&*it;
+        out_hull[k++] = &*it;
+    }
+    
+    /* upper hull */
+    size_t t = k+1;
+    for (Points::const_iterator it = points.end() - 2; it != points.begin(); --it) {
+        while (k >= t && it->ccw(out_hull[k-2], out_hull[k-1]) <= 0) --k;
+        out_hull[k++] = &*it;
+    }
+    
+    // we assume hull is empty
+    hull.points.reserve(k);
+    for (size_t i = 0; i < k; ++i) {
+        hull.points.push_back(*(out_hull[i]));
+    }
+    
+    free(out_hull);
+}
+
+}