WIP: Optimization of the object's 2D convex silhouette for arrangement,

not working yet.

src/libslic3r/Model.cpp

@@ -912,6 +912,60 @@ BoundingBoxf3 ModelObject::instance_bounding_box(size_t instance_idx, bool dont_
     return bb;
 }
 
+// Calculate 2D convex hull of of a projection of the transformed printable volumes into the XY plane.
+// This method is cheap in that it does not make any unnecessary copy of the volume meshes.
+// This method is used by the auto arrange function.
+Polygon ModelObject::convex_hull_2d(const Transform3d &trafo_instance)
+{
+    Points pts;
+    for (const ModelVolume *v : this->volumes)
+        if (v->is_model_part()) {
+            const stl_file &stl = v->mesh.stl;
+            Transform3d trafo = trafo_instance * v->get_matrix();
+            if (stl.v_shared == nullptr) {
+                // Using the STL faces.
+                for (unsigned int i = 0; i < stl.stats.number_of_facets; ++ i) {
+                    const stl_facet &facet = stl.facet_start[i];
+                    for (size_t j = 0; j < 3; ++ j) {
+                        Vec3d p = trafo * facet.vertex[j].cast<double>();
+                        pts.emplace_back(coord_t(scale_(p.x())), coord_t(scale_(p.y())));
+                    }
+                }
+            } else {
+                // Using the shared vertices should be a bit quicker than using the STL faces.
+                for (int i = 0; i < stl.stats.shared_vertices; ++ i) {           
+                    Vec3d p = trafo * stl.v_shared[i].cast<double>();
+                    pts.emplace_back(coord_t(scale_(p.x())), coord_t(scale_(p.y())));
+                }
+            }
+        }
+	std::sort(pts.begin(), pts.end(), [](const Point& a, const Point& b) { return a(0) < b(0) || (a(0) == b(0) && a(1) < b(1)); });
+	pts.erase(std::unique(pts.begin(), pts.end(), [](const Point& a, const Point& b) { return a(0) == b(0) && a(1) == b(1); }), pts.end());
+
+    Polygon hull;
+    int n = (int)pts.size();
+    if (n >= 3) {
+        int k = 0;
+        hull.points.resize(2 * n);
+        // Build lower hull
+        for (int i = 0; i < n; ++ i) {
+            while (k >= 2 && pts[i].ccw(hull[k-2], hull[k-1]) <= 0)
+                -- k;
+            hull[k ++] = pts[i];
+        }
+        // Build upper hull
+        for (int i = n-2, t = k+1; i >= 0; i--) {
+            while (k >= t && pts[i].ccw(hull[k-2], hull[k-1]) <= 0)
+                -- k;
+            hull[k ++] = pts[i];
+        }
+        hull.points.resize(k);
+        assert(hull.points.front() == hull.points.back());
+        hull.points.pop_back();
+    }
+    return hull;
+}
+
 void ModelObject::center_around_origin()
 {
     // calculate the displacements needed to 
@@ -1099,7 +1153,7 @@ ModelObjectPtrs ModelObject::cut(size_t instance, coordf_t z, bool keep_upper, b
 
             // Perform cut
             TriangleMeshSlicer tms(&volume->mesh);
-            tms.cut(z, &upper_mesh, &lower_mesh);
+            tms.cut(float(z), &upper_mesh, &lower_mesh);
 
             // Reset volume transformation except for offset
             const Vec3d offset = volume->get_offset();