basic purpose: 1. refresh knowledge how to interact qml - c++; 2. make bindings c++ to qml; 3. make custom elements via c++ and qml; used resources: 0. https://doc.qt.io/qt-5/qtqml-tutorials-extending-qml-example.html; 1. https://www.youtube.com/watch?v=8wj9relIrcs&list=PLvItDmb0sZw_l5qKMLTjePXX485CWKVNe&index=7; 2. https://github.com/cneben/QuickQanava;