auto adj = ui::Adjustment( 30, -90, 90, 1, 10, 0 );
adj.connect( "value_changed", G_CALLBACK( preview_spin ), &elevation );
spin = ui::SpinButton( adj, 1, 0 );
gtk_widget_show( spin );
auto adj = ui::Adjustment( 30, -90, 90, 1, 10, 0 );
adj.connect( "value_changed", G_CALLBACK( preview_spin ), &elevation );
spin = ui::SpinButton( adj, 1, 0 );
gtk_widget_show( spin );