[mapguide-internals] Possible optimization in ajax viewer: do not call the server if the resulting image does not change

[Gabriele Monfardini]

I'm using Mapguide 2.2 and AJAX Viewer

If I change the visibility of a layer in a non visible group or change
the visibility of a group that has no visible layer inside it would be
better to avoid calling the server.

Regards,

Gabriele