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

not working yet.

src/libslic3r/Geometry.cpp

@@ -207,8 +207,7 @@ static bool sort_pointfs(const Vec3d& a, const Vec3d& b)
 }
 
 // This implementation is based on Andrew's monotone chain 2D convex hull algorithm
-Polygon
-convex_hull(Points points)
+Polygon convex_hull(Points points)
 {
     assert(points.size() >= 3);
     // sort input points

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();

src/libslic3r/Model.hpp

@@ -223,6 +223,12 @@ public:
 	BoundingBoxf3 raw_mesh_bounding_box() const;
 	// A snug bounding box of non-transformed (non-rotated, non-scaled, non-translated) sum of all object volumes.
     BoundingBoxf3 full_raw_mesh_bounding_box() const;
+
+    // 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       convex_hull_2d(const Transform3d &trafo_instance);
+
     void center_around_origin();
     void ensure_on_bed();
     void translate_instances(const Vec3d& vector);

src/libslic3r/ModelArrange.cpp

@@ -553,6 +553,12 @@ ShapeData2D projectModelFromTop(const Slic3r::Model &model) {
     for(ModelObject* objptr : model.objects) {
         if(objptr) {
 
+            // TODO export the exact 2D projection. Cannot do it as libnest2d
+            // does not support concave shapes (yet).
+            ClipperLib::Path clpath;
+//WIP Vojtech's optimization of the calculation of the convex hull is not working correctly yet.
+#if 1
+            {
                 TriangleMesh rmesh = objptr->raw_mesh();
 
                 ModelInstance * finst = objptr->instances.front();
@@ -570,7 +576,24 @@ ShapeData2D projectModelFromTop(const Slic3r::Model &model) {
 
                 p.make_clockwise();
                 p.append(p.first_point());
-            auto clpath = Slic3rMultiPoint_to_ClipperPath(p);
+                clpath = Slic3rMultiPoint_to_ClipperPath(p);
+            }
+#else
+            // Object instances should carry the same scaling and
+            // x, y rotation that is why we use the first instance.
+            {
+                ModelInstance *finst = objptr->instances.front();
+                Vec3d rotation = finst->get_rotation();
+                rotation.z() = 0.;
+                Transform3d trafo_instance = Geometry::assemble_transform(Vec3d::Zero(), rotation, finst->get_scaling_factor(), finst->get_mirror());
+                Polygon p = objptr->convex_hull_2d(trafo_instance);
+				assert(! p.points.empty());
+				p.reverse();
+				assert(! p.is_counter_clockwise());
+                p.append(p.first_point());
+                clpath = Slic3rMultiPoint_to_ClipperPath(p);
+            }
+#endif
 
             for(ModelInstance* objinst : objptr->instances) {
                 if(objinst) {