The edit-and-run paradigm for demos of graph algorithms requires an explicit user action, namely clicking the done-button, to start the graph algorithm to be demonstrated. Call-back or handler functions allow us to write online demos which show the result of a graph algorithm while the graph is edited.

If the edges of your graph have capacities or costs, have a look at A Recipe for Online Demos of Network Algorithms with GraphWin

We use a function run_and_display() that runs the graph algorithm on the graph associated with GraphWin gw and updates the display. We define post-handlers for the new_node, new_edge, del_node, del_edge, and init_graph operations; each handler simply calls run_and_display(gw). In the main() function we tell GraphWin which handlers to use by calling the corresponding set_handler() functions, display the GraphWin, and call gw.edit().

We derive a specific demo from this framework by instantiating the run_and_display() function with a call to STRONG_COMPONENTS() and coloring the nodes according to their component.

The picture above shows a screenshot of the program after some edit operations. Clicking on the pictures shows the Graphwin in original size.

#include <LEDA/graphics/graphwin.h>
#include <LEDA/graph/graph_alg.h>

using namespace leda;

void run_and_display(GraphWin& gw);

void new_node_handler(GraphWin& gw, node) {run_and_display(gw);}
void new_edge_handler(GraphWin& gw, edge) {run_and_display(gw);}
void del_edge_handler(GraphWin& gw) {run_and_display(gw);}
void del_node_handler(GraphWin& gw) {run_and_display(gw);}
void init_graph_handler(GraphWin& gw) {run_and_display(gw);}

int main()
{
  GraphWin gw;

  gw.set_init_graph_handler(init_graph_handler);
  gw.set_new_edge_handler(new_edge_handler);
  gw.set_del_edge_handler(del_edge_handler);
  gw.set_new_node_handler(new_node_handler);
  gw.set_del_node_handler(del_node_handler);

  gw.display();gw.edit();

  return 0;
}

void run_and_display(GraphWin& gw)
{
  graph& G=gw.get_graph();
  node_array<int> comp_num(G);
  STRONG_COMPONENTS(G,comp_num);

  node v;forall_nodes(v,G) 
    gw.set_color(v,color(comp_num[v]));
}