The callback of a state change binding is evaluated when certain states change, as specified at binding creation.
l_bind_state(target, event, callback)
either an object of class loon or a vector that specifies the
widget, layer, glyph, navigator or context completely. The widget is
specified by the widget path name (e.g.
vector with state names
callback function is an R function which is called by the Tcl interpreter if the event of interest happens. Note that in loon the callback functions support different optional arguments depending on the binding type, read the details for more information
state change binding id
Bindings, callbacks, and binding substitutions are described in detail in
loon's documentation webpage, i.e. run