Interactive utilities for the Gtk toolkit (Julia)
Author JuliaGtk
5 Stars
Updated Last
1 Year Ago
Started In
July 2015


Build Status


New users are encouraged to consider GtkReactive instead.

What is GtkUtilities?

This package is a collection of extensions to Gtk that make interactive graphics easier. For example, it allows you to:

  • "attach" user data to widgets or any other object
  • perform rubber-band selection
  • use pan and zoom
  • synchronize state across multiple UI widgets and canvases


Install via

]add GtkUtilities


guidata: associating user data with widgets

Given a widget (Button, Canvas, Window, etc.) or other graphical object w, a value val can be associated with ("stored in") w using

guidata[w, :name] = val

where :name is the name (a Symbol) you've assigned to val for the purposes of storage.

The value can be retrieved with

val = guidata[w, :name]

Here are some other things you can do with guidata:

alldata = guidata[w]           # fetch all data associated with w
val = get(guidata, (w,:name), default)   # returns default if :name not defined
delete!(guidata, (w,:name))    # deletes the value associated with :name
delete!(guidata, w)            # deletes all data associated with w

If w is a GtkWidget, the associated data are automatically deleted when the object is destroyed.


    c = @Canvas()
    bb = BoundingBox(0, 1, 0, 1)
    guidata[c, :zoombb] = bb

Rubber band selection

rubberband_start(c, x, y, callback_done; minpixels=2) starts a rubber-band selection on Canvas c at position (x,y). When the user releases the mouse button, the callback function callback_done(c, bb) is run, where bb is the BoundingBox of the selected region. To reduce the likelihood that clicks used to raise windows will result in rubber banding, the callback is not executed unless the user drags the mouse by at least minpixels pixels (default value 2).


    c.mouse.button1press = (widget, event) -> begin
        if event.event_type == Gtk.GdkEventType.BUTTON_PRESS
            GtkUtilities.rubberband_start(c, event.x, event.y, (c, bb) -> @show bb)

sets up a Canvas so that rubberband selection starts when the user clicks the mouse; when the button is released, it prints the bounding box of the selection region.

Zooming and panning

Zooming and panning a Canvas c are performed using four guidata objects, named :xview, :yview, :xviewlimits, :yviewlimits. The first two express the current view region, which includes effects of any previous zoom and pan operations. The second two encode the allowable area, representing the largest-sized region that may be viewed.

You intialize panning and zooming with

panzoom(c, [xviewlimits, yviewlimits], [xview, yview])
id = panzoom_key(c)

This sequence will implement panning and zooming with either the keyboard or wheel-mouse. You can specify the keys and modifiers, as well as the behavior of scroll-zooming relative to the mouse pointer location, via keyword arguments to these functions. See each individual function (e.g., ?panzoom_key) for more information.

The draw method for your Canvas must make use of the :xview, :yview properties. In the simplest cases, you might achieve this with

draw(c) do widget
ctx = getgc(c)
h = height(c)
w = width(c)

xviewlimits, yviewlimits = guidata[c, :xviewlimits], guidata[c, :yviewlimits]
bb = BoundingBox( xviewlimits.min, xviewlimits.max, yviewlimits.min, yviewlimits.max)  # you can create bb outside of the draw method instead, by using explicity values for xview/yview-limits. However, 'guidata' will not work unless 'c' has already been fully defined.
set_coordinates(ctx, BoundingBox(0, w, 0, h), bb)

xview, yview = guidata[c, :xview], guidata[c, :yview]
# use xview and yview to manipulate the content of your canvas

The returned id can be disabled or enabled via signal_handler_block and signal_handler_unblock, respectively, or removed with signal_handler_disconnect.

Managing state

Note: this component will be rebased on Reactive.jl after JuliaGizmos/Reactive.jl#65 merges, hopefully via This interface is deprecated.

Suppose you have a slider (a Scale) and an Entry box as two alternative mechanisms for specifying a single number, and you want to use that number in some calculations when you render a Canvas. Who "owns" the number? Does the Entry callback have to be aware of the Scale callback, and vice-versa?

You can centralize your handling of this piece of information by using a State object and linking it to the UI elements:

state = State(5)

e = @Entry()
s = @Scale(false, 1:10)
c = @Canvas()
draw(c) do widget
   ...   # make use of state in here somewhere

elink = link(state, e)
slink = link(state, s)
link(state, c)

get(elink)               # returns 5
set!(state, 7)           # wow, the Canvas redraws and the Entry & Scale change!
get(state)               # returns 7
get(slink)               # returns 7
set!(slink, 4)           # everything updates again

Note that in this example we didn't have to write any callbacks at all: just linking the widget to the State object creates the callback we need, and any changes are automatically propagated for you.


Each function has its own help, e.g., ?rubberband_start.