gtk-tree-view-set-column-drag-function (view func)

view -- a gtk-tree-view widget
func -- a callback function to determine which columns are reorderable, or nil

Sets a user callback function of type gtk-tree-view-column-drop-func for determining where a column may be dropped when dragged. This function is called on every column pair in turn at the beginning of a column drag to determine where a drop can take place. The arguments passed to func are: the gtk-tree-view widget, the gtk-tree-view-column object being dragged, and the two gtk-tree-view-column objects determining the drop spot. If either of the gtk-tree-view-column arguments for the drop spot are nil, then they indicate an edge. If func is set to be nil, then view reverts to the default behavior of allowing all columns to be dropped everywhere.