def generate_layout(bpmn_graph):
    """
    :param bpmn_graph: an instance of BPMNDiagramGraph class.
    """
    classification = generate_elements_clasification(bpmn_graph)
    (sorted_nodes_with_classification, backward_flows) = topological_sort(bpmn_graph, classification[0])
    grid = grid_layout(bpmn_graph, sorted_nodes_with_classification)
    set_coordinates_for_nodes(bpmn_graph, grid)
    set_flows_waypoints(bpmn_graph)
:param bpmn_graph: an instance of BPMNDiagramGraph class.