Description The GtkSourceGutter object represents the left and right gutters of the text view. It is used by GtkSourceView to draw the line numbers and category marks that might be present on a line. By packing additional GtkCellRenderer objects in the gutter, you can extend the gutter with your own custom drawings. The gutter works very much the same way as cells rendered in a GtkTreeView. The concept is similar, with the exception that the gutter does not have an underlying GtkTreeModel. Instead, you should use gtk_source_gutter_set_cell_data_func to set a callback to fill in any of the cell renderers properties, given the line for which the cell is to be rendered. Renderers are inserted into the gutter at a certain position. The builtin line number renderer is at position GTK_SOURCE_VIEW_GUTTER_POSITION_LINES (-30) and the marks renderer is at GTK_SOURCE_VIEW_GUTTER_POSITION_MARKS (-20). You can use these values to position custom renderers accordingly. The width of a cell renderer can be specified as either fixed (using gtk_cell_renderer_set_fixed_size) or dynamic, in which case you must set gtk_source_gutter_set_cell_size_func. This callback is used to set the properties of the renderer such that gtk_cell_renderer_get_size yields the maximum width of the cell.