Initial implementation of MeshClipper class

So far the work is shared between the old code in GLGizmoSlaSupports.cpp and the new class

src/slic3r/GUI/MeshClipper.cpp

@@ -0,0 +1,83 @@
+#include "MeshClipper.hpp"
+#include "GLCanvas3D.hpp"
+#include "libslic3r/Tesselate.hpp"
+
+namespace Slic3r {
+namespace GUI {
+
+void MeshClipper::set_plane(const ClippingPlane& plane)
+{
+    if (m_plane != plane) {
+        m_plane = plane;
+        m_triangles_valid = false;
+    }
+}
+
+void MeshClipper::set_mesh(const TriangleMesh& mesh)
+{
+    if (m_mesh != &mesh) {
+        m_mesh = &mesh;
+        m_triangles_valid = false;
+        m_triangles.resize(0);
+        m_tms.reset(nullptr);
+    }
+}
+
+void MeshClipper::set_transformation(const Geometry::Transformation& trafo)
+{
+    if (! m_trafo.get_matrix().isApprox(trafo.get_matrix())) {
+        m_trafo = trafo;
+        m_triangles_valid = false;
+        m_triangles.resize(0);
+    }
+}
+
+
+const std::vector<Vec2f>& MeshClipper::get_triangles()
+{
+    if (! m_triangles_valid)
+        recalculate_triangles();
+
+    return m_triangles;
+}
+
+void MeshClipper::recalculate_triangles()
+{
+    if (! m_tms) {
+        m_tms.reset(new TriangleMeshSlicer);
+        m_tms->init(m_mesh, [](){});
+    }
+
+
+    auto up_and_height = get_mesh_cut_normal();
+    Vec3f up = up_and_height.first;
+    float height_mesh = up_and_height.second;
+
+    std::vector<ExPolygons> list_of_expolys;
+    m_tms->set_up_direction(up);
+    m_tms->slice(std::vector<float>{height_mesh}, 0.f, &list_of_expolys, [](){});
+    m_triangles = triangulate_expolygons_2f(list_of_expolys[0]);
+
+    m_triangles_valid = true;
+}
+
+std::pair<Vec3f, float> MeshClipper::get_mesh_cut_normal() const
+{
+    Transform3f instance_matrix_no_translation_no_scaling = m_trafo.get_matrix(true,false,true).cast<float>();
+    Vec3f scaling = m_trafo.get_scaling_factor().cast<float>();
+
+    // Calculate distance from mesh origin to the clipping plane (in mesh coordinates).
+    Vec3f up_noscale = instance_matrix_no_translation_no_scaling.inverse() * m_plane.get_normal().cast<float>();
+    Vec3f up (up_noscale(0)*scaling(0), up_noscale(1)*scaling(1), up_noscale(2)*scaling(2));
+
+    float height_mesh = m_plane.distance(m_trafo.get_offset()) * (up_noscale.norm()/up.norm());
+
+
+    return std::make_pair(up, height_mesh);
+}
+
+
+
+
+} // namespace GUI
+} // namespace Slic3r