Toolkit implementation of gWidgets for tcltk


Port of gWidgets API to tcltk. The gWidgets API is an abstract, lightweight means to interact with GUI toolkits. In this case, the tcltk toolkit.


This file documents differences between gWidgetstcltk and the gWidgets API, which is documented both in the man pages for that package and in its vignette. The gWidgetstcltk package is not as complete as gWidgetsRGtk2. This is due to limitations in the base libraries implementing tcl/tk. This package was designed to work with the limited version that comes with the standard Windows installation of R.

Notes on this implementation:

The primary difference in this interface, as opposed to that for RGtk2, is that each widget requires a container when being constructed. The container is given to the container argument. The value may be the logical TRUE indicating that a new window is constructed, or a container widget.

Other differences are that tcltk does not seem to have a markup language like Pango for GTK or HTML for JAVA, as such the markup argument for several widgets that is used to format text is not available. The font<- method can substitute.

Until version 8.5 of tk, the basic tcltk installation did not include several widgets that appear in other toolkits. For instance a grid widget, a notebook widget, etc. This package now requires tk 8.5 to work and R 2.12-0 or newer.


gwindow(): The width= and height= arguments refer to the minimum window size, not the preferred default size. It is best to set visible=FALSE for the constructor and then when the GUI is layed out call visible<-. This will get the proper size for the window. Otherwse, the update method can be called to resize the window to accomodate the child widgets.

The methods addHandlerDestroy and addHandlerUnrealize can only add one handler, new ones overwrite the old. These handlers can also not be removed.

ggroup() has the expand= fill= and anchor= arguments. If expand=TRUE the widget is allocated as much space as possible. (The default is expand=FALSE, unless the option "gw:tcltkDefaultExpand" overrides this.) When a widget has expand, then the widget may stretch to fill the expanding space (in tcltk, all widgets that have expand=TRUE are allocated evenly any additional space). The fill may be TRUE (or both), FALSE, or "x" and "y". The anchor= argument adjusts a widget left or right, up or down, within its space. Only one component works at a time for the anchor argument. In a horizontal box, only the y component can be used to move a value up or down. In a vertical box, only the x component can be used to move a value left or right. The default is c(-1,0) so that horizontal layouts are towards the middle, and vertical layouts towards the left. (This can be overridden: options("gw:tcltkDefaultAnchor"=c(0,0)), say.)

The use.scrollwindows feature is now implemented. (but seems buggy)

The addSpring method only works if the parent container is set to expand.

gframe() The markup argument is ignored. Use font<- to give the title markup.

gexpandgroup() Works as expected, although sizing issues may frustrate.

gdfnotebook() Works with the addition of ttknotebook. The add method, which is used to add pages, is called when the notebook is given as a container during the construction of a widget. Hence, to add a page something like this is done:

  nb <- gnotebook(cont=gwindow("Notebook example"))
  gbutton("Page 1", cont=nb, label = "tab1")
  glabel("Page 2", cont=nb, label = "tab2")
  gedit("Page 3", cont=nb, label = "tab3")

glayout() has two additional arguments: expand=TRUE is like expand= for ggroup(), in that the attached widget expands to fill the possible space in the container. If this isn't given the anchor= argument can be used to adjust the location of the widget withing the cell. A value of c(-1,1) is the lower left, c(-1,1) the upper left (the default), c(1,-1) the lower right, and c(1,1) the upper right. The value 0 for either is also possible.

gpanedgroup() The constructor is called with no widgets. To add a widget to the paned group the paned group is passed as a container, as in

  pg <- gpanedgroup(container=gwindow("example"), horizontal = FALSE)
  b1 = gbutton("button 1", container=pg)
  b2 = gbutton("button 2", container=pg)

The paned window can be adjusted manually or using the svalue method. The svalue method uses the current window size. If the widget is not realized, the method will not work as expected, so call this after showing the GUI. The delete method can be used to delete a widget. It may be added back with the add method.

The basic widgets or components: (These are also known as controls)

gbutton() mostly works. The button won't resize to take up all the possible space for a widget, even if expand=TRUE is given.

gcalendar() is a hack.

gcheckbox() works as advertised, use.togglebutton implemented.

gcheckboxgroup() works as advertised, except the use.table argument is ignored. One can now resize the list.

gcombobox() Works as expected, although no icons or tooltips are available.

gdf() is implemented if the user has installed the tktable package in Tcl. This is an additional download from Most of the code comes second hand from tcltk2's dfedit function.

gedit(): The widget does not resize automatically. Set the width with width= at time of construction or with size<-. There is now type ahead support, although the pop-down menu only pops down, so don't use near the bottom of a screen ;) The hidden argument init_msg can be used to place an initial message for the event there is no text in the box.

gfilebrowse() works.

ggraphics() Not implemented. The tkrplot package could be used in some way, but this does not provide a fully embeddable graphics device. The tkrplot package provides a means to create interactive graphics with tcltk. This is not a device, so ins't directly supported. However, a ggroup object can be used as a parent container. Just call getToolkitWidget on the object first:

g <- ggroup(cont=gwindow())
l <- tkrplot(getToolkitWidget(g), function() hist(rnorm(100)))
add(g, l)

ghelp() Works as advertised. Uses a popup menu instead of a notebook, as gWidgetsRGtk2. Best to just use helpr though.

gimage() Only works with gif and pnm files, as the underlying tcltk widget only uses these by default.

glabel() No markup available. Use font<- instead.

gmenu() adds only to the top window, not any container. This is a tcltk limitation. Use a popupmenu instead.

Under Mac OS X, menus display in the top menu bar area, not in the parent window.

gtoolbar() A hack made from a ggroup object that packs in gbutton instances. The buttons take up alot of screen real estate, on the default Aqua them of OS X the buttons are rounded, so the toolbar looks odd, ...

gaction() is implemented for buttons, menubars and toolbars. The key.accel component is now implemented but one must pass in a parent argument (The binding is to the top-level window containing the parent).

gradio() has an extra argument coerce.with=, as otherwise it would treat everything as a character vector. It tries to guess when instantiated, if not explicitly given. One can now resize the number of items to select from.

gseparator() works as expected but must be in a container with expand=TRUE.

gslider() now works with non-integer steps. If first argument from is a vector it will slide over those values after sorting. This uses a themed widget which might be buggy under some styles.

gspinbutton() Works as expected. The change handler responds to clicks of the arrows or to the return key in the text area. Unless one has a new Tk version, this is a non-themed widget and can look a bit odd.

gstatusbar() A hack. Just a ggroup() instance in disguise. By default it must have a gwindow instance for a parent container. If the hidden argument not.toplevel=TRUE is specified, a ggroup container may be used.

gtable() This is built on the underlying tree widget. It is not ideal, but avoids needing to have a separate library (eg. Tktable) installed. If the hidden argument round is passed to the constructor, this will be passed to the format function's digits argument when formatting numeric values for display.

Sizing is an issue. There may be a bug in the widget regarding horizontal scrolling (for Mac OS X anyways, where this is being developed), or more likely something is just coded wrong. There is some Tk code for "autoscrolling" that works (with an idiosyncrasy) so that the initial size of the widget is correct, but only when this size is set via arguments width and height passed to the constructor – not with the size<- method. This feature is not on by default, as when it is used any widgets on the right of the table are not shown in the initial window, and are only exposed by resizing the window. If you want to try it, pass in the hidden argument do.autoscroll=TRUE. However, the size<- method has another use. It can also take a list for value. This list has optional components width, height, columnWidths (to specify each column width individually), and noRowsVisible (to specify height by number of rows, not pixels).

gtext() The size<- method can be used to resize the widget. The initial default size is quite large. This method guesses at the converstion from pixels to characters (width) and lines of text (height) used by the underlying widget. The svalue() method returns all the text unless some text is selected by the mouse and : index=TRUE in which case the indices of the selected text are returned or drop=TRUE in which case only the selected text is returned.

gtree() Implemented using ttktreeview. It is slow however, so use on smaller trees only. Has same issues with scrollbars as gtable.

Compound components:

gcommandline() is implemented, but could definitely be improved.

ghelpbrowser() just calls ghelp

ggenericwidget() Some kinks need ironing out when the main variable is a formula.

gdfnotebook() Not implemented.

ggraphicsnotebook() No ggraphics so no notebook.

gvarbrowser() Uses a tree to show heirarchical structure of workspace. Does not poll to update workspace. It does reread workspace when Filter by: value is changed.

Dialogs: (These are modal, hence they have no methods (basically).)

gfile() works as advertised.

galert() works.

gmessage() works.

gconfirm() works.

ginput() works.

gbasicdialog() is implemented. It it is a container. When the visible(obj,TRUE) command is issued, the container is shown and made modal.

dlg <- gbasicdialog("A modal dialog", handler=function(h,...) print("hi"))
l = glabel("some widget in the dialog", cont=dlg)
visible(dlg, set=TRUE)


Handlers were rewritten so that one can have more than one handler per signal. The blockHandler, unblockHandler and removeHandler methods are now working. Handler code different for those widgets which use an R5 backend and those which don't, but the end user shouldn't notice. (Well, if you do let me know!)

The addHandlerBlur method should be called when a widget loses focuses, but here is called whenever a widget loses focus and whenever the mouse leaves the widget. This can mean the handler is called twice. If you don'l like that, you can add the callback through addHandler(obj, signal, handler) where signal is <FocusOut> or <Leave>.

adddroptarget(), adddropsource(), and adddropmotion work for tcltk widgets. The cursor changes to a funny looking cursor, but nothing resembling a drag and drop cursor. One was chosen from the standard cursors. Dragging from other applications is not supported.


John Verzani. Several code segments were inspired by the examples of Wettenhall and the Dalgaard article referenced below. The drag and drop code was modified from code at Icons were "borrowed" from several places: the scigraphica project, KDE, and elsewhere.

Maintainer: John Verzani <>


Peter Dalgaard's RNews article on the tcltk pagkage; Several examples on; The PERL documentation was useful:, although this is for the most part a translation of the TK documentation.

For a package somewhat similar in intent see Bowman, Crawford, Alexander, and Bowman's rpanel package: or the tkWidgets package of Zhang

The fgui package provides a similar functionality as ggenericwidget in a standalone package.


## Not run: 
## select CRAN miror example
setMirror = function(URL) {
   repos = getOption("repos")
   repos["CRAN"] = gsub("/$", "", URL)
   options(repos = repos)

  win = gwindow("Select a CRAN mirror")
  tbl = gtable(utils:::getCRANmirrors(), 
  handler = function(h,...) {
    URL = svalue(h$obj)

## End(Not run)
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