]> January 24th, 2003 Tony Gale Ian Main & the GTK team This is a tutorial on how to use GTK (the GIMP Toolkit) through its C interface. A copy of this tutorial in SGML and HTML is distributed with each source code release of GTK+. For binary distributions, please check with your vendor. A copy is available online for reference at http://www.gtk.org/tutorial. A packaged verion of this tutorial is available from ftp://ftp.gtk.org/pub/gtk/tutorial which contains the tutorial in various different formats. This package is primary for those people wanting to have the tutorial available for offline reference and for printing. GTK (GIMP Toolkit) is a library for creating graphical user interfaces. It is licensed using the LGPL license, so you can develop open software, free software, or even commercial non-free software using GTK without having to spend anything for licenses or royalties. It's called the GIMP toolkit because it was originally written for developing the GNU Image Manipulation Program (GIMP), but GTK has now been used in a large number of software projects, including the GNU Network Object Model Environment (GNOME) project. GTK is built on top of GDK (GIMP Drawing Kit) which is basically a wrapper around the low-level functions for accessing the underlying windowing functions (Xlib in the case of the X windows system), and gdk-pixbuf, a library for client-side image manipulation. The primary authors of GTK are: Peter Mattis petm@xcf.berkeley.edu Spencer Kimball spencer@xcf.berkeley.edu Josh MacDonald jmacd@xcf.berkeley.edu GTK is currently maintained by: Owen Taylor otaylor@redhat.com Tim Janik timj@gtk.org GTK is essentially an object oriented application programmers interface (API). Although written completely in C, it is implemented using the idea of classes and callback functions (pointers to functions). There is also a third component called GLib which contains a few replacements for some standard calls, as well as some additional functions for handling linked lists, etc. The replacement functions are used to increase GTK's portability, as some of the functions implemented here are not available or are nonstandard on other Unixes such as g_strerror(). Some also contain enhancements to the libc versions, such as g_malloc() that has enhanced debugging utilities. In version 2.0, GLib has picked up the type system which forms the foundation for GTK's class hierarchy, the signal system which is used throughout GTK, a thread API which abstracts the different native thread APIs of the various platforms and a facility for loading modules. As the last component, GTK uses the Pango library for internationalized text output. This tutorial describes the C interface to GTK. There are GTK bindings for many other languages including C++, Guile, Perl, Python, TOM, Ada95, Objective C, Free Pascal, Eiffel, Java and C#. If you intend to use another language's bindings to GTK, look at that binding's documentation first. In some cases that documentation may describe some important conventions (which you should know first) and then refer you back to this tutorial. There are also some cross-platform APIs (such as wxWindows and V) which use GTK as one of their target platforms; again, consult their documentation first. If you're developing your GTK application in C++, a few extra notes are in order. There's a C++ binding to GTK called GTK--, which provides a more C++-like interface to GTK; you should probably look into this instead. If you don't like that approach for whatever reason, there are two alternatives for using GTK. First, you can use only the C subset of C++ when interfacing with GTK and then use the C interface as described in this tutorial. Second, you can use GTK and C++ together by declaring all callbacks as static functions in C++ classes, and again calling GTK using its C interface. If you choose this last approach, you can include as the callback's data value a pointer to the object to be manipulated (the so-called "this" value). Selecting between these options is simply a matter of preference, since in all three approaches you get C++ and GTK. None of these approaches requires the use of a specialized preprocessor, so no matter what you choose you can use standard C++ with GTK. This tutorial is an attempt to document as much as possible of GTK, but it is by no means complete. This tutorial assumes a good understanding of C, and how to create C programs. It would be a great benefit for the reader to have previous X programming experience, but it shouldn't be necessary. If you are learning GTK as your first widget set, please comment on how you found this tutorial, and what you had trouble with. There are also C++, Objective C, ADA, Guile and other language bindings available, but I don't follow these. This document is a "work in progress". Please look for updates on http://www.gtk.org/. I would very much like to hear of any problems you have learning GTK from this document, and would appreciate input as to how it may be improved. Please see the section on Contributing for further information. The first thing to do, of course, is download the GTK source and install it. You can always get the latest version from ftp.gtk.org. You can also view other sources of GTK information on http://www.gtk.org/. GTK uses GNU autoconf for configuration. Once untar'd, type ./configure --help to see a list of options. The GTK source distribution also contains the complete source to all of the examples used in this tutorial, along with Makefiles to aid compilation. To begin our introduction to GTK, we'll start with the simplest program possible. This program will create a 200x200 pixel window and has no way of exiting except to be killed by using the shell. #include <gtk/gtk.h> int main( int argc, char *argv[] ) { GtkWidget *window; gtk_init (&argc, &argv); window = gtk_window_new (GTK_WINDOW_TOPLEVEL); gtk_widget_show (window); gtk_main (); return 0; } You can compile the above program with gcc using: gcc base.c -o base `pkg-config --cflags --libs gtk+-2.0` The meaning of the unusual compilation options is explained below in Compiling Hello World. All programs will of course include gtk/gtk.h which declares the variables, functions, structures, etc. that will be used in your GTK application. The next line: gtk_init (&argc, &argv); calls the function gtk_init(gint *argc, gchar ***argv) which will be called in all GTK applications. This sets up a few things for us such as the default visual and color map and then proceeds to call gdk_init(gint *argc, gchar ***argv). This function initializes the library for use, sets up default signal handlers, and checks the arguments passed to your application on the command line, looking for one of the following: --gtk-module --g-fatal-warnings --gtk-debug --gtk-no-debug --gdk-debug --gdk-no-debug --display --sync --name --class It removes these from the argument list, leaving anything it does not recognize for your application to parse or ignore. This creates a set of standard arguments accepted by all GTK applications. The next two lines of code create and display a window. window = gtk_window_new (GTK_WINDOW_TOPLEVEL); gtk_widget_show (window); The GTK_WINDOW_TOPLEVEL argument specifies that we want the window to undergo window manager decoration and placement. Rather than create a window of 0x0 size, a window without children is set to 200x200 by default so you can still manipulate it. The gtk_widget_show() function lets GTK know that we are done setting the attributes of this widget, and that it can display it. The last line enters the GTK main processing loop. gtk_main (); gtk_main() is another call you will see in every GTK application. When control reaches this point, GTK will sleep waiting for X events (such as button or key presses), timeouts, or file IO notifications to occur. In our simple example, however, events are ignored. Now for a program with a widget (a button). It's the classic hello world a la GTK. #include <gtk/gtk.h> /* This is a callback function. The data arguments are ignored * in this example. More on callbacks below. */ static void hello( GtkWidget *widget, gpointer data ) { g_print ("Hello World\n"); } static gboolean delete_event( GtkWidget *widget, GdkEvent *event, gpointer data ) { /* If you return FALSE in the "delete_event" signal handler, * GTK will emit the "destroy" signal. Returning TRUE means * you don't want the window to be destroyed. * This is useful for popping up 'are you sure you want to quit?' * type dialogs. */ g_print ("delete event occurred\n"); /* Change TRUE to FALSE and the main window will be destroyed with * a "delete_event". */ return TRUE; } /* Another callback */ static void destroy( GtkWidget *widget, gpointer data ) { gtk_main_quit (); } int main( int argc, char *argv[] ) { /* GtkWidget is the storage type for widgets */ GtkWidget *window; GtkWidget *button; /* This is called in all GTK applications. Arguments are parsed * from the command line and are returned to the application. */ gtk_init (&argc, &argv); /* create a new window */ window = gtk_window_new (GTK_WINDOW_TOPLEVEL); /* When the window is given the "delete_event" signal (this is given * by the window manager, usually by the "close" option, or on the * titlebar), we ask it to call the delete_event () function * as defined above. The data passed to the callback * function is NULL and is ignored in the callback function. */ g_signal_connect (G_OBJECT (window), "delete_event", G_CALLBACK (delete_event), NULL); /* Here we connect the "destroy" event to a signal handler. * This event occurs when we call gtk_widget_destroy() on the window, * or if we return FALSE in the "delete_event" callback. */ g_signal_connect (G_OBJECT (window), "destroy", G_CALLBACK (destroy), NULL); /* Sets the border width of the window. */ gtk_container_set_border_width (GTK_CONTAINER (window), 10); /* Creates a new button with the label "Hello World". */ button = gtk_button_new_with_label ("Hello World"); /* When the button receives the "clicked" signal, it will call the * function hello() passing it NULL as its argument. The hello() * function is defined above. */ g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (hello), NULL); /* This will cause the window to be destroyed by calling * gtk_widget_destroy(window) when "clicked". Again, the destroy * signal could come from here, or the window manager. */ g_signal_connect_swapped (G_OBJECT (button), "clicked", G_CALLBACK (gtk_widget_destroy), G_OBJECT (window)); /* This packs the button into the window (a gtk container). */ gtk_container_add (GTK_CONTAINER (window), button); /* The final step is to display this newly created widget. */ gtk_widget_show (button); /* and the window */ gtk_widget_show (window); /* All GTK applications must have a gtk_main(). Control ends here * and waits for an event to occur (like a key press or * mouse event). */ gtk_main (); return 0; } To compile use: gcc -Wall -g helloworld.c -o helloworld `pkg-config --cflags gtk+-2.0` \ `pkg-config --libs gtk+-2.0` This uses the program pkg-config, which can be obtained from www.freedesktop.org. This program reads the .pc which comes with GTK to determine what compiler switches are needed to compile programs that use GTK. pkg-config --cflags gtk+-2.0 will output a list of include directories for the compiler to look in, and pkg-config --libs gtk+-2.0 will output the list of libraries for the compiler to link with and the directories to find them in. In the above example they could have been combined into a single instance, such as pkg-config --cflags --libs gtk+-2.0. Note that the type of single quote used in the compile command above is significant. The libraries that are usually linked in are: The GTK library (-lgtk), the widget library, based on top of GDK. The GDK library (-lgdk), the Xlib wrapper. The gdk-pixbuf library (-lgdk_pixbuf), the image manipulation library. The Pango library (-lpango) for internationalized text. The gobject library (-lgobject), containing the type system on which GTK is based. The gmodule library (-lgmodule), which is used to load run time extensions. The GLib library (-lglib), containing miscellaneous functions; only g_print() is used in this particular example. GTK is built on top of GLib so you will always require this library. See the section on GLib for details. The Xlib library (-lX11) which is used by GDK. The Xext library (-lXext). This contains code for shared memory pixmaps and other X extensions. The math library (-lm). This is used by GTK for various purposes. In version 2.0, the signal system has been moved from GTK to GLib, therefore the functions and types explained in this section have a "g_" prefix rather than a "gtk_" prefix. We won't go into details about the extensions which the GLib 2.0 signal system has relative to the GTK 1.2 signal system. Before we look in detail at helloworld, we'll discuss signals and callbacks. GTK is an event driven toolkit, which means it will sleep in gtk_main() until an event occurs and control is passed to the appropriate function. This passing of control is done using the idea of "signals". (Note that these signals are not the same as the Unix system signals, and are not implemented using them, although the terminology is almost identical.) When an event occurs, such as the press of a mouse button, the appropriate signal will be "emitted" by the widget that was pressed. This is how GTK does most of its useful work. There are signals that all widgets inherit, such as "destroy", and there are signals that are widget specific, such as "toggled" on a toggle button. To make a button perform an action, we set up a signal handler to catch these signals and call the appropriate function. This is done by using a function such as: gulong g_signal_connect( gpointer *object, const gchar *name, GCallback func, gpointer func_data ); where the first argument is the widget which will be emitting the signal, and the second the name of the signal you wish to catch. The third is the function you wish to be called when it is caught, and the fourth, the data you wish to have passed to this function. The function specified in the third argument is called a "callback function", and should generally be of the form void callback_func( GtkWidget *widget, gpointer callback_data ); where the first argument will be a pointer to the widget that emitted the signal, and the second a pointer to the data given as the last argument to the g_signal_connect() function as shown above. Note that the above form for a signal callback function declaration is only a general guide, as some widget specific signals generate different calling parameters. Another call used in the helloworld example, is: gulong g_signal_connect_swapped( gpointer *object, const gchar *name, GCallback func, gpointer *slot_object ); g_signal_connect_swapped() is the same as g_signal_connect() except that the callback function only uses one argument, a pointer to a GTK object. So when using this function to connect signals, the callback should be of the form void callback_func( GtkObject *object ); where the object is usually a widget. We usually don't setup callbacks for g_signal_connect_swapped() however. They are usually used to call a GTK function that accepts a single widget or object as an argument, as is the case in our helloworld example. The purpose of having two functions to connect signals is simply to allow the callbacks to have a different number of arguments. Many functions in the GTK library accept only a single GtkWidget pointer as an argument, so you want to use the g_signal_connect_swapped() for these, whereas for your functions, you may need to have additional data supplied to the callbacks. In addition to the signal mechanism described above, there is a set of events that reflect the X event mechanism. Callbacks may also be attached to these events. These events are: event button_press_event button_release_event scroll_event motion_notify_event delete_event destroy_event expose_event key_press_event key_release_event enter_notify_event leave_notify_event configure_event focus_in_event focus_out_event map_event unmap_event property_notify_event selection_clear_event selection_request_event selection_notify_event proximity_in_event proximity_out_event visibility_notify_event client_event no_expose_event window_state_event In order to connect a callback function to one of these events you use the function g_signal_connect(), as described above, using one of the above event names as the name parameter. The callback function for events has a slightly different form than that for signals: gint callback_func( GtkWidget *widget, GdkEvent *event, gpointer callback_data ); GdkEvent is a C union structure whose type will depend upon which of the above events has occurred. In order for us to tell which event has been issued each of the possible alternatives has a type member that reflects the event being issued. The other components of the event structure will depend upon the type of the event. Possible values for the type are: GDK_NOTHING GDK_DELETE GDK_DESTROY GDK_EXPOSE GDK_MOTION_NOTIFY GDK_BUTTON_PRESS GDK_2BUTTON_PRESS GDK_3BUTTON_PRESS GDK_BUTTON_RELEASE GDK_KEY_PRESS GDK_KEY_RELEASE GDK_ENTER_NOTIFY GDK_LEAVE_NOTIFY GDK_FOCUS_CHANGE GDK_CONFIGURE GDK_MAP GDK_UNMAP GDK_PROPERTY_NOTIFY GDK_SELECTION_CLEAR GDK_SELECTION_REQUEST GDK_SELECTION_NOTIFY GDK_PROXIMITY_IN GDK_PROXIMITY_OUT GDK_DRAG_ENTER GDK_DRAG_LEAVE GDK_DRAG_MOTION GDK_DRAG_STATUS GDK_DROP_START GDK_DROP_FINISHED GDK_CLIENT_EVENT GDK_VISIBILITY_NOTIFY GDK_NO_EXPOSE GDK_SCROLL GDK_WINDOW_STATE GDK_SETTING So, to connect a callback function to one of these events we would use something like: g_signal_connect (G_OBJECT (button), "button_press_event", G_CALLBACK (button_press_callback), NULL); This assumes that button is a Button widget. Now, when the mouse is over the button and a mouse button is pressed, the function button_press_callback() will be called. This function may be declared as: static gboolean button_press_callback( GtkWidget *widget, GdkEventButton *event, gpointer data ); Note that we can declare the second argument as type GdkEventButton as we know what type of event will occur for this function to be called. The value returned from this function indicates whether the event should be propagated further by the GTK event handling mechanism. Returning TRUE indicates that the event has been handled, and that it should not propagate further. Returning FALSE continues the normal event handling. See the section on Advanced Event and Signal Handling for more details on this propagation process. For details on the GdkEvent data types, see the appendix entitled GDK Event Types. The GDK selection and drag-and-drop APIs also emit a number of events which are reflected in GTK by the signals. See Signals on the source widget and Signals on the destination widget for details on the signatures of the callback functions for these signals: selection_received selection_get drag_begin_event drag_end_event drag_data_delete drag_motion drag_drop drag_data_get drag_data_received Now that we know the theory behind this, let's clarify by walking through the example helloworld program. Here is the callback function that will be called when the button is "clicked". We ignore both the widget and the data in this example, but it is not hard to do things with them. The next example will use the data argument to tell us which button was pressed. static void hello( GtkWidget *widget, gpointer data ) { g_print ("Hello World\n"); } The next callback is a bit special. The "delete_event" occurs when the window manager sends this event to the application. We have a choice here as to what to do about these events. We can ignore them, make some sort of response, or simply quit the application. The value you return in this callback lets GTK know what action to take. By returning TRUE, we let it know that we don't want to have the "destroy" signal emitted, keeping our application running. By returning FALSE, we ask that "destroy" be emitted, which in turn will call our "destroy" signal handler. static gboolean delete_event( GtkWidget *widget, GdkEvent *event, gpointer data ) { g_print ("delete event occurred\n"); return TRUE; } Here is another callback function which causes the program to quit by calling gtk_main_quit(). This function tells GTK that it is to exit from gtk_main when control is returned to it. static void destroy( GtkWidget *widget, gpointer data ) { gtk_main_quit (); } I assume you know about the main() function... yes, as with other applications, all GTK applications will also have one of these. int main( int argc, char *argv[] ) { This next part declares pointers to a structure of type GtkWidget. These are used below to create a window and a button. GtkWidget *window; GtkWidget *button; Here is our gtk_init() again. As before, this initializes the toolkit, and parses the arguments found on the command line. Any argument it recognizes from the command line, it removes from the list, and modifies argc and argv to make it look like they never existed, allowing your application to parse the remaining arguments. gtk_init (&argc, &argv); Create a new window. This is fairly straightforward. Memory is allocated for the GtkWidget *window structure so it now points to a valid structure. It sets up a new window, but it is not displayed until we call gtk_widget_show(window) near the end of our program. window = gtk_window_new (GTK_WINDOW_TOPLEVEL); Here are two examples of connecting a signal handler to an object, in this case, the window. Here, the "delete_event" and "destroy" signals are caught. The first is emitted when we use the window manager to kill the window, or when we use the gtk_widget_destroy() call passing in the window widget as the object to destroy. The second is emitted when, in the "delete_event" handler, we return FALSE. The G_OBJECT and G_CALLBACK are macros that perform type casting and checking for us, as well as aid the readability of the code. g_signal_connect (G_OBJECT (window), "delete_event", G_CALLBACK (delete_event), NULL); g_signal_connect (G_OBJECT (window), "destroy", G_CALLBACK (destroy), NULL); This next function is used to set an attribute of a container object. This just sets the window so it has a blank area along the inside of it 10 pixels wide where no widgets will go. There are other similar functions which we will look at in the section on Setting Widget Attributes And again, GTK_CONTAINER is a macro to perform type casting. gtk_container_set_border_width (GTK_CONTAINER (window), 10); This call creates a new button. It allocates space for a new GtkWidget structure in memory, initializes it, and makes the button pointer point to it. It will have the label "Hello World" on it when displayed. button = gtk_button_new_with_label ("Hello World"); Here, we take this button, and make it do something useful. We attach a signal handler to it so when it emits the "clicked" signal, our hello() function is called. The data is ignored, so we simply pass in NULL to the hello() callback function. Obviously, the "clicked" signal is emitted when we click the button with our mouse pointer. g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (hello), NULL); We are also going to use this button to exit our program. This will illustrate how the "destroy" signal may come from either the window manager, or our program. When the button is "clicked", same as above, it calls the first hello() callback function, and then this one in the order they are set up. You may have as many callback functions as you need, and all will be executed in the order you connected them. Because the gtk_widget_destroy() function accepts only a GtkWidget *widget as an argument, we use the g_signal_connect_swapped() function here instead of straight g_signal_connect(). g_signal_connect_swapped (G_OBJECT (button), "clicked", G_CALLBACK (gtk_widget_destroy), G_OBJECT (window)); This is a packing call, which will be explained in depth later on in Packing Widgets. But it is fairly easy to understand. It simply tells GTK that the button is to be placed in the window where it will be displayed. Note that a GTK container can only contain one widget. There are other widgets, that are described later, which are designed to layout multiple widgets in various ways. gtk_container_add (GTK_CONTAINER (window), button); Now we have everything set up the way we want it to be. With all the signal handlers in place, and the button placed in the window where it should be, we ask GTK to "show" the widgets on the screen. The window widget is shown last so the whole window will pop up at once rather than seeing the window pop up, and then the button form inside of it. Although with such a simple example, you'd never notice. gtk_widget_show (button); gtk_widget_show (window); And of course, we call gtk_main() which waits for events to come from the X server and will call on the widgets to emit signals when these events come. gtk_main (); And the final return. Control returns here after gtk_quit() is called. return 0; Now, when we click the mouse button on a GTK button, the widget emits a "clicked" signal. In order for us to use this information, our program sets up a signal handler to catch that signal, which dispatches the function of our choice. In our example, when the button we created is "clicked", the hello() function is called with a NULL argument, and then the next handler for this signal is called. This calls the gtk_widget_destroy() function, passing it the window widget as its argument, destroying the window widget. This causes the window to emit the "destroy" signal, which is caught, and calls our destroy() callback function, which simply exits GTK. Another course of events is to use the window manager to kill the window, which will cause the "delete_event" to be emitted. This will call our "delete_event" handler. If we return TRUE here, the window will be left as is and nothing will happen. Returning FALSE will cause GTK to emit the "destroy" signal which of course calls the "destroy" callback, exiting GTK. There are a few things you probably noticed in the previous examples that need explaining. The gint, gchar, etc. that you see are typedefs to int and char, respectively, that are part of the GLib system. This is done to get around that nasty dependency on the size of simple data types when doing calculations. A good example is "gint32" which will be typedef'd to a 32 bit integer for any given platform, whether it be the 64 bit alpha, or the 32 bit i386. The typedefs are very straightforward and intuitive. They are all defined in glib/glib.h (which gets included from gtk.h). You'll also notice GTK's ability to use GtkWidget when the function calls for a GtkObject. GTK is an object oriented design, and a widget is an object. Lets take another look at the g_signal_connect() declaration. gulong g_signal_connect( gpointer object, const gchar *name, GCallback func, gpointer func_data ); Notice the gulong return value? This is a tag that identifies your callback function. As stated above, you may have as many callbacks per signal and per object as you need, and each will be executed in turn, in the order they were attached. This tag allows you to remove this callback from the list by using: void g_signal_handler_disconnect( gpointer object, gulong id ); So, by passing in the widget you wish to remove the handler from, and the tag returned by one of the signal_connect functions, you can disconnect a signal handler. You can also temporarily disable signal handlers with the g_signal_handler_block() and g_signal_handler_unblock() family of functions. void g_signal_handler_block( gpointer object, gulong id ); void g_signal_handlers_block_by_func( gpointer object, GCallback func, gpointer data ); void g_signal_handler_unblock( gpointer object, gulong id ); void g_signal_handlers_unblock_by_func( gpointer object, GCallback func, gpointer data ); Let's take a look at a slightly improved helloworld with better examples of callbacks. This will also introduce us to our next topic, packing widgets. #include <gtk/gtk.h> /* Our new improved callback. The data passed to this function * is printed to stdout. */ static void callback( GtkWidget *widget, gpointer data ) { g_print ("Hello again - %s was pressed\n", (gchar *) data); } /* another callback */ static gboolean delete_event( GtkWidget *widget, GdkEvent *event, gpointer data ) { gtk_main_quit (); return FALSE; } int main( int argc, char *argv[] ) { /* GtkWidget is the storage type for widgets */ GtkWidget *window; GtkWidget *button; GtkWidget *box1; /* This is called in all GTK applications. Arguments are parsed * from the command line and are returned to the application. */ gtk_init (&argc, &argv); /* Create a new window */ window = gtk_window_new (GTK_WINDOW_TOPLEVEL); /* This is a new call, which just sets the title of our * new window to "Hello Buttons!" */ gtk_window_set_title (GTK_WINDOW (window), "Hello Buttons!"); /* Here we just set a handler for delete_event that immediately * exits GTK. */ g_signal_connect (G_OBJECT (window), "delete_event", G_CALLBACK (delete_event), NULL); /* Sets the border width of the window. */ gtk_container_set_border_width (GTK_CONTAINER (window), 10); /* We create a box to pack widgets into. This is described in detail * in the "packing" section. The box is not really visible, it * is just used as a tool to arrange widgets. */ box1 = gtk_hbox_new (FALSE, 0); /* Put the box into the main window. */ gtk_container_add (GTK_CONTAINER (window), box1); /* Creates a new button with the label "Button 1". */ button = gtk_button_new_with_label ("Button 1"); /* Now when the button is clicked, we call the "callback" function * with a pointer to "button 1" as its argument */ g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (callback), (gpointer) "button 1"); /* Instead of gtk_container_add, we pack this button into the invisible * box, which has been packed into the window. */ gtk_box_pack_start (GTK_BOX(box1), button, TRUE, TRUE, 0); /* Always remember this step, this tells GTK that our preparation for * this button is complete, and it can now be displayed. */ gtk_widget_show (button); /* Do these same steps again to create a second button */ button = gtk_button_new_with_label ("Button 2"); /* Call the same callback function with a different argument, * passing a pointer to "button 2" instead. */ g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (callback), (gpointer) "button 2"); gtk_box_pack_start(GTK_BOX (box1), button, TRUE, TRUE, 0); /* The order in which we show the buttons is not really important, but I * recommend showing the window last, so it all pops up at once. */ gtk_widget_show (button); gtk_widget_show (box1); gtk_widget_show (window); /* Rest in gtk_main and wait for the fun to begin! */ gtk_main (); return 0; } Compile this program using the same linking arguments as our first example. You'll notice this time there is no easy way to exit the program, you have to use your window manager or command line to kill it. A good exercise for the reader would be to insert a third "Quit" button that will exit the program. You may also wish to play with the options to gtk_box_pack_start() while reading the next section. Try resizing the window, and observe the behavior. When creating an application, you'll want to put more than one widget inside a window. Our first helloworld example only used one widget so we could simply use a gtk_container_add() call to "pack" the widget into the window. But when you want to put more than one widget into a window, how do you control where that widget is positioned? This is where packing comes in. Most packing is done by creating boxes. These are invisible widget containers that we can pack our widgets into which come in two forms, a horizontal box, and a vertical box. When packing widgets into a horizontal box, the objects are inserted horizontally from left to right or right to left depending on the call used. In a vertical box, widgets are packed from top to bottom or vice versa. You may use any combination of boxes inside or beside other boxes to create the desired effect. To create a new horizontal box, we use a call to gtk_hbox_new(), and for vertical boxes, gtk_vbox_new(). The gtk_box_pack_start() and gtk_box_pack_end() functions are used to place objects inside of these containers. The gtk_box_pack_start() function will start at the top and work its way down in a vbox, and pack left to right in an hbox. gtk_box_pack_end() will do the opposite, packing from bottom to top in a vbox, and right to left in an hbox. Using these functions allows us to right justify or left justify our widgets and may be mixed in any way to achieve the desired effect. We will use gtk_box_pack_start() in most of our examples. An object may be another container or a widget. In fact, many widgets are actually containers themselves, including the button, but we usually only use a label inside a button. By using these calls, GTK knows where you want to place your widgets so it can do automatic resizing and other nifty things. There are also a number of options as to how your widgets should be packed. As you can imagine, this method gives us a quite a bit of flexibility when placing and creating widgets. Because of this flexibility, packing boxes in GTK can be confusing at first. There are a lot of options, and it's not immediately obvious how they all fit together. In the end, however, there are basically five different styles. Each line contains one horizontal box (hbox) with several buttons. The call to gtk_box_pack is shorthand for the call to pack each of the buttons into the hbox. Each of the buttons is packed into the hbox the same way (i.e., same arguments to the gtk_box_pack_start() function). This is the declaration of the gtk_box_pack_start() function. void gtk_box_pack_start( GtkBox *box, GtkWidget *child, gboolean expand, gboolean fill, guint padding ); The first argument is the box you are packing the object into, the second is the object. The objects will all be buttons for now, so we'll be packing buttons into boxes. The expand argument to gtk_box_pack_start() and gtk_box_pack_end() controls whether the widgets are laid out in the box to fill in all the extra space in the box so the box is expanded to fill the area allotted to it (TRUE); or the box is shrunk to just fit the widgets (FALSE). Setting expand to FALSE will allow you to do right and left justification of your widgets. Otherwise, they will all expand to fit into the box, and the same effect could be achieved by using only one of gtk_box_pack_start() or gtk_box_pack_end(). The fill argument to the gtk_box_pack functions control whether the extra space is allocated to the objects themselves (TRUE), or as extra padding in the box around these objects (FALSE). It only has an effect if the expand argument is also TRUE. When creating a new box, the function looks like this: GtkWidget *gtk_hbox_new ( gboolean homogeneous, gint spacing ); The homogeneous argument to gtk_hbox_new() (and the same for gtk_vbox_new()) controls whether each object in the box has the same size (i.e., the same width in an hbox, or the same height in a vbox). If it is set, the gtk_box_pack() routines function essentially as if the expand argument was always turned on. What's the difference between spacing (set when the box is created) and padding (set when elements are packed)? Spacing is added between objects, and padding is added on either side of an object. The following figure should make it clearer: Here is the code used to create the above images. I've commented it fairly heavily so I hope you won't have any problems following it. Compile it yourself and play with it. /* example-start packbox packbox.c */ #include <stdio.h> #include <stdlib.h> #include "gtk/gtk.h" static gboolean delete_event( GtkWidget *widget, GdkEvent *event, gpointer data ) { gtk_main_quit (); return FALSE; } /* Make a new hbox filled with button-labels. Arguments for the * variables we're interested are passed in to this function. * We do not show the box, but do show everything inside. */ static GtkWidget *make_box( gboolean homogeneous, gint spacing, gboolean expand, gboolean fill, guint padding ) { GtkWidget *box; GtkWidget *button; char padstr[80]; /* Create a new hbox with the appropriate homogeneous * and spacing settings */ box = gtk_hbox_new (homogeneous, spacing); /* Create a series of buttons with the appropriate settings */ button = gtk_button_new_with_label ("gtk_box_pack"); gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding); gtk_widget_show (button); button = gtk_button_new_with_label ("(box,"); gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding); gtk_widget_show (button); button = gtk_button_new_with_label ("button,"); gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding); gtk_widget_show (button); /* Create a button with the label depending on the value of * expand. */ if (expand == TRUE) button = gtk_button_new_with_label ("TRUE,"); else button = gtk_button_new_with_label ("FALSE,"); gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding); gtk_widget_show (button); /* This is the same as the button creation for "expand" * above, but uses the shorthand form. */ button = gtk_button_new_with_label (fill ? "TRUE," : "FALSE,"); gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding); gtk_widget_show (button); sprintf (padstr, "%d);", padding); button = gtk_button_new_with_label (padstr); gtk_box_pack_start (GTK_BOX (box), button, expand, fill, padding); gtk_widget_show (button); return box; } int main( int argc, char *argv[]) { GtkWidget *window; GtkWidget *button; GtkWidget *box1; GtkWidget *box2; GtkWidget *separator; GtkWidget *label; GtkWidget *quitbox; int which; /* Our init, don't forget this! :) */ gtk_init (&argc, &argv); if (argc != 2) { fprintf (stderr, "usage: packbox num, where num is 1, 2, or 3.\n"); /* This just does cleanup in GTK and exits with an exit status of 1. */ exit (1); } which = atoi (argv[1]); /* Create our window */ window = gtk_window_new (GTK_WINDOW_TOPLEVEL); /* You should always remember to connect the delete_event signal * to the main window. This is very important for proper intuitive * behavior */ g_signal_connect (G_OBJECT (window), "delete_event", G_CALLBACK (delete_event), NULL); gtk_container_set_border_width (GTK_CONTAINER (window), 10); /* We create a vertical box (vbox) to pack the horizontal boxes into. * This allows us to stack the horizontal boxes filled with buttons one * on top of the other in this vbox. */ box1 = gtk_vbox_new (FALSE, 0); /* which example to show. These correspond to the pictures above. */ switch (which) { case 1: /* create a new label. */ label = gtk_label_new ("gtk_hbox_new (FALSE, 0);"); /* Align the label to the left side. We'll discuss this function and * others in the section on Widget Attributes. */ gtk_misc_set_alignment (GTK_MISC (label), 0, 0); /* Pack the label into the vertical box (vbox box1). Remember that * widgets added to a vbox will be packed one on top of the other in * order. */ gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 0); /* Show the label */ gtk_widget_show (label); /* Call our make box function - homogeneous = FALSE, spacing = 0, * expand = FALSE, fill = FALSE, padding = 0 */ box2 = make_box (FALSE, 0, FALSE, FALSE, 0); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); /* Call our make box function - homogeneous = FALSE, spacing = 0, * expand = TRUE, fill = FALSE, padding = 0 */ box2 = make_box (FALSE, 0, TRUE, FALSE, 0); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); /* Args are: homogeneous, spacing, expand, fill, padding */ box2 = make_box (FALSE, 0, TRUE, TRUE, 0); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); /* Creates a separator, we'll learn more about these later, * but they are quite simple. */ separator = gtk_hseparator_new (); /* Pack the separator into the vbox. Remember each of these * widgets is being packed into a vbox, so they'll be stacked * vertically. */ gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5); gtk_widget_show (separator); /* Create another new label, and show it. */ label = gtk_label_new ("gtk_hbox_new (TRUE, 0);"); gtk_misc_set_alignment (GTK_MISC (label), 0, 0); gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 0); gtk_widget_show (label); /* Args are: homogeneous, spacing, expand, fill, padding */ box2 = make_box (TRUE, 0, TRUE, FALSE, 0); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); /* Args are: homogeneous, spacing, expand, fill, padding */ box2 = make_box (TRUE, 0, TRUE, TRUE, 0); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); /* Another new separator. */ separator = gtk_hseparator_new (); /* The last 3 arguments to gtk_box_pack_start are: * expand, fill, padding. */ gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5); gtk_widget_show (separator); break; case 2: /* Create a new label, remember box1 is a vbox as created * near the beginning of main() */ label = gtk_label_new ("gtk_hbox_new (FALSE, 10);"); gtk_misc_set_alignment (GTK_MISC (label), 0, 0); gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 0); gtk_widget_show (label); /* Args are: homogeneous, spacing, expand, fill, padding */ box2 = make_box (FALSE, 10, TRUE, FALSE, 0); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); /* Args are: homogeneous, spacing, expand, fill, padding */ box2 = make_box (FALSE, 10, TRUE, TRUE, 0); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); separator = gtk_hseparator_new (); /* The last 3 arguments to gtk_box_pack_start are: * expand, fill, padding. */ gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5); gtk_widget_show (separator); label = gtk_label_new ("gtk_hbox_new (FALSE, 0);"); gtk_misc_set_alignment (GTK_MISC (label), 0, 0); gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 0); gtk_widget_show (label); /* Args are: homogeneous, spacing, expand, fill, padding */ box2 = make_box (FALSE, 0, TRUE, FALSE, 10); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); /* Args are: homogeneous, spacing, expand, fill, padding */ box2 = make_box (FALSE, 0, TRUE, TRUE, 10); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); separator = gtk_hseparator_new (); /* The last 3 arguments to gtk_box_pack_start are: expand, fill, padding. */ gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5); gtk_widget_show (separator); break; case 3: /* This demonstrates the ability to use gtk_box_pack_end() to * right justify widgets. First, we create a new box as before. */ box2 = make_box (FALSE, 0, FALSE, FALSE, 0); /* Create the label that will be put at the end. */ label = gtk_label_new ("end"); /* Pack it using gtk_box_pack_end(), so it is put on the right * side of the hbox created in the make_box() call. */ gtk_box_pack_end (GTK_BOX (box2), label, FALSE, FALSE, 0); /* Show the label. */ gtk_widget_show (label); /* Pack box2 into box1 (the vbox remember ? :) */ gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, FALSE, 0); gtk_widget_show (box2); /* A separator for the bottom. */ separator = gtk_hseparator_new (); /* This explicitly sets the separator to 400 pixels wide by 5 pixels * high. This is so the hbox we created will also be 400 pixels wide, * and the "end" label will be separated from the other labels in the * hbox. Otherwise, all the widgets in the hbox would be packed as * close together as possible. */ gtk_widget_set_size_request (separator, 400, 5); /* pack the separator into the vbox (box1) created near the start * of main() */ gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 5); gtk_widget_show (separator); } /* Create another new hbox.. remember we can use as many as we need! */ quitbox = gtk_hbox_new (FALSE, 0); /* Our quit button. */ button = gtk_button_new_with_label ("Quit"); /* Setup the signal to terminate the program when the button is clicked */ g_signal_connect_swapped (G_OBJECT (button), "clicked", G_CALLBACK (gtk_main_quit), G_OBJECT (window)); /* Pack the button into the quitbox. * The last 3 arguments to gtk_box_pack_start are: * expand, fill, padding. */ gtk_box_pack_start (GTK_BOX (quitbox), button, TRUE, FALSE, 0); /* pack the quitbox into the vbox (box1) */ gtk_box_pack_start (GTK_BOX (box1), quitbox, FALSE, FALSE, 0); /* Pack the vbox (box1) which now contains all our widgets, into the * main window. */ gtk_container_add (GTK_CONTAINER (window), box1); /* And show everything left */ gtk_widget_show (button); gtk_widget_show (quitbox); gtk_widget_show (box1); /* Showing the window last so everything pops up at once. */ gtk_widget_show (window); /* And of course, our main function. */ gtk_main (); /* Control returns here when gtk_main_quit() is called, but not when * exit() is used. */ return 0; } Let's take a look at another way of packing - Tables. These can be extremely useful in certain situations. Using tables, we create a grid that we can place widgets in. The widgets may take up as many spaces as we specify. The first thing to look at, of course, is the gtk_table_new() function: GtkWidget *gtk_table_new( guint rows, guint columns, gboolean homogeneous ); The first argument is the number of rows to make in the table, while the second, obviously, is the number of columns. The homogeneous argument has to do with how the table's boxes are sized. If homogeneous is TRUE, the table boxes are resized to the size of the largest widget in the table. If homogeneous is FALSE, the size of a table boxes is dictated by the tallest widget in its same row, and the widest widget in its column. The rows and columns are laid out from 0 to n, where n was the number specified in the call to gtk_table_new. So, if you specify rows = 2 and columns = 2, the layout would look something like this: 0 1 2 0+----------+----------+ | | | 1+----------+----------+ | | | 2+----------+----------+ Note that the coordinate system starts in the upper left hand corner. To place a widget into a box, use the following function: void gtk_table_attach( GtkTable *table, GtkWidget *child, guint left_attach, guint right_attach, guint top_attach, guint bottom_attach, GtkAttachOptions xoptions, GtkAttachOptions yoptions, guint xpadding, guint ypadding ); The first argument ("table") is the table you've created and the second ("child") the widget you wish to place in the table. The left and right attach arguments specify where to place the widget, and how many boxes to use. If you want a button in the lower right table entry of our 2x2 table, and want it to fill that entry only, left_attach would be = 1, right_attach = 2, top_attach = 1, bottom_attach = 2. Now, if you wanted a widget to take up the whole top row of our 2x2 table, you'd use left_attach = 0, right_attach = 2, top_attach = 0, bottom_attach = 1. The xoptions and yoptions are used to specify packing options and may be bitwise OR'ed together to allow multiple options. These options are: GTK_FILL If the table box is larger than the widget, and GTK_FILL is specified, the widget will expand to use all the room available. GTK_SHRINK If the table widget was allocated less space then was requested (usually by the user resizing the window), then the widgets would normally just be pushed off the bottom of the window and disappear. If GTK_SHRINK is specified, the widgets will shrink with the table. GTK_EXPAND This will cause the table to expand to use up any remaining space in the window. Padding is just like in boxes, creating a clear area around the widget specified in pixels. gtk_table_attach() has a lot of options. So, there's a shortcut: void gtk_table_attach_defaults( GtkTable *table, GtkWidget *widget, guint left_attach, guint right_attach, guint top_attach, guint bottom_attach ); The X and Y options default to GTK_FILL | GTK_EXPAND, and X and Y padding are set to 0. The rest of the arguments are identical to the previous function. We also have gtk_table_set_row_spacing() and gtk_table_set_col_spacing(). These places spacing between the rows at the specified row or column. void gtk_table_set_row_spacing( GtkTable *table, guint row, guint spacing ); and void gtk_table_set_col_spacing ( GtkTable *table, guint column, guint spacing ); Note that for columns, the space goes to the right of the column, and for rows, the space goes below the row. You can also set a consistent spacing of all rows and/or columns with: void gtk_table_set_row_spacings( GtkTable *table, guint spacing ); And, void gtk_table_set_col_spacings( GtkTable *table, guint spacing ); Note that with these calls, the last row and last column do not get any spacing. Here we make a window with three buttons in a 2x2 table. The first two buttons will be placed in the upper row. A third, quit button, is placed in the lower row, spanning both columns. Which means it should look something like this: Here's the source code: #include <gtk/gtk.h> /* Our callback. * The data passed to this function is printed to stdout */ static void callback( GtkWidget *widget, gpointer data ) { g_print ("Hello again - %s was pressed\n", (char *) data); } /* This callback quits the program */ static gboolean delete_event( GtkWidget *widget, GdkEvent *event, gpointer data ) { gtk_main_quit (); return FALSE; } int main( int argc, char *argv[] ) { GtkWidget *window; GtkWidget *button; GtkWidget *table; gtk_init (&argc, &argv); /* Create a new window */ window = gtk_window_new (GTK_WINDOW_TOPLEVEL); /* Set the window title */ gtk_window_set_title (GTK_WINDOW (window), "Table"); /* Set a handler for delete_event that immediately * exits GTK. */ g_signal_connect (G_OBJECT (window), "delete_event", G_CALLBACK (delete_event), NULL); /* Sets the border width of the window. */ gtk_container_set_border_width (GTK_CONTAINER (window), 20); /* Create a 2x2 table */ table = gtk_table_new (2, 2, TRUE); /* Put the table in the main window */ gtk_container_add (GTK_CONTAINER (window), table); /* Create first button */ button = gtk_button_new_with_label ("button 1"); /* When the button is clicked, we call the "callback" function * with a pointer to "button 1" as its argument */ g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (callback), (gpointer) "button 1"); /* Insert button 1 into the upper left quadrant of the table */ gtk_table_attach_defaults (GTK_TABLE (table), button, 0, 1, 0, 1); gtk_widget_show (button); /* Create second button */ button = gtk_button_new_with_label ("button 2"); /* When the button is clicked, we call the "callback" function * with a pointer to "button 2" as its argument */ g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (callback), (gpointer) "button 2"); /* Insert button 2 into the upper right quadrant of the table */ gtk_table_attach_defaults (GTK_TABLE (table), button, 1, 2, 0, 1); gtk_widget_show (button); /* Create "Quit" button */ button = gtk_button_new_with_label ("Quit"); /* When the button is clicked, we call the "delete_event" function * and the program exits */ g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (delete_event), NULL); /* Insert the quit button into the both * lower quadrants of the table */ gtk_table_attach_defaults (GTK_TABLE (table), button, 0, 2, 1, 2); gtk_widget_show (button); gtk_widget_show (table); gtk_widget_show (window); gtk_main (); return 0; } The general steps to creating a widget in GTK are: gtk_*_new() - one of various functions to create a new widget. These are all detailed in this section. Connect all signals and events we wish to use to the appropriate handlers. Set the attributes of the widget. Pack the widget into a container using the appropriate call such as gtk_container_add() or gtk_box_pack_start(). gtk_widget_show() the widget. gtk_widget_show() lets GTK know that we are done setting the attributes of the widget, and it is ready to be displayed. You may also use gtk_widget_hide to make it disappear again. The order in which you show the widgets is not important, but I suggest showing the window last so the whole window pops up at once rather than seeing the individual widgets come up on the screen as they're formed. The children of a widget (a window is a widget too) will not be displayed until the window itself is shown using the gtk_widget_show() function. You'll notice as you go on that GTK uses a type casting system. This is always done using macros that both test the ability to cast the given item, and perform the cast. Some common ones you will see are: G_OBJECT (object) GTK_WIDGET (widget) GTK_OBJECT (object) GTK_SIGNAL_FUNC (function) GTK_CONTAINER (container) GTK_WINDOW (window) GTK_BOX (box) These are all used to cast arguments in functions. You'll see them in the examples, and can usually tell when to use them simply by looking at the function's declaration. As you can see below in the class hierarchy, all GtkWidgets are derived from the GObject base class. This means you can use a widget in any place the function asks for an object - simply use the G_OBJECT() macro. For example: g_signal_connect( G_OBJECT (button), "clicked", G_CALLBACK (callback_function), callback_data); This casts the button into an object, and provides a cast for the function pointer to the callback. Many widgets are also containers. If you look in the class hierarchy below, you'll notice that many widgets derive from the Container class. Any one of these widgets may be used with the GTK_CONTAINER macro to pass them to functions that ask for containers. Unfortunately, these macros are not extensively covered in the tutorial, but I recommend taking a look through the GTK header files or the GTK API reference manual. It can be very educational. In fact, it's not difficult to learn how a widget works just by looking at the function declarations. For your reference, here is the class hierarchy tree used to implement widgets. (Deprecated widgets and auxiliary classes have been omitted.) GObject | GtkObject +GtkWidget | +GtkMisc | | +GtkLabel | | | `GtkAccelLabel | | +GtkArrow | | `GtkImage | +GtkContainer | | +GtkBin | | | +GtkAlignment | | | +GtkFrame | | | | `GtkAspectFrame | | | +GtkButton | | | | +GtkToggleButton | | | | | `GtkCheckButton | | | | | `GtkRadioButton | | | | `GtkOptionMenu | | | +GtkItem | | | | +GtkMenuItem | | | | +GtkCheckMenuItem | | | | | `GtkRadioMenuItem | | | | +GtkImageMenuItem | | | | +GtkSeparatorMenuItem | | | | `GtkTearoffMenuItem | | | +GtkWindow | | | | +GtkDialog | | | | | +GtkColorSelectionDialog | | | | | +GtkFileSelection | | | | | +GtkFontSelectionDialog | | | | | +GtkInputDialog | | | | | `GtkMessageDialog | | | | `GtkPlug | | | +GtkEventBox | | | +GtkHandleBox | | | +GtkScrolledWindow | | | `GtkViewport | | +GtkBox | | | +GtkButtonBox | | | | +GtkHButtonBox | | | | `GtkVButtonBox | | | +GtkVBox | | | | +GtkColorSelection | | | | +GtkFontSelection | | | | `GtkGammaCurve | | | `GtkHBox | | | +GtkCombo | | | `GtkStatusbar | | +GtkFixed | | +GtkPaned | | | +GtkHPaned | | | `GtkVPaned | | +GtkLayout | | +GtkMenuShell | | | +GtkMenuBar | | | `GtkMenu | | +GtkNotebook | | +GtkSocket | | +GtkTable | | +GtkTextView | | +GtkToolbar | | `GtkTreeView | +GtkCalendar | +GtkDrawingArea | | `GtkCurve | +GtkEditable | | +GtkEntry | | `GtkSpinButton | +GtkRuler | | +GtkHRuler | | `GtkVRuler | +GtkRange | | +GtkScale | | | +GtkHScale | | | `GtkVScale | | `GtkScrollbar | | +GtkHScrollbar | | `GtkVScrollbar | +GtkSeparator | | +GtkHSeparator | | `GtkVSeparator | +GtkInvisible | +GtkPreview | `GtkProgressBar +GtkAdjustment +GtkCellRenderer | +GtkCellRendererPixbuf | +GtkCellRendererText | +GtkCellRendererToggle +GtkItemFactory +GtkTooltips `GtkTreeViewColumn The following widgets do not have an associated window. If you want to capture events, you'll have to use the EventBox. See the section on the EventBox widget. GtkAlignment GtkArrow GtkBin GtkBox GtkButton GtkCheckButton GtkFixed GtkImage GtkLabel GtkMenuItem GtkNotebook GtkPaned GtkRadioButton GtkRange GtkScrolledWindow GtkSeparator GtkTable GtkToolbar GtkAspectFrame GtkFrame GtkVBox GtkHBox GtkVSeparator GtkHSeparator We'll further our exploration of GTK by examining each widget in turn, creating a few simple functions to display them. Another good source is the testgtk program that comes with GTK. It can be found in tests/testgtk.c. We've almost seen all there is to see of the button widget. It's pretty simple. There is however more than one way to create a button. You can use the gtk_button_new_with_label() or gtk_button_new_with_mnemonic() to create a button with a label, use gtk_button_new_from_stock() to create a button containing the image and text from a stock item or use gtk_button_new() to create a blank button. It's then up to you to pack a label or pixmap into this new button. To do this, create a new box, and then pack your objects into this box using the usual gtk_box_pack_start(), and then use gtk_container_add() to pack the box into the button. Here's an example of using gtk_button_new() to create a button with a image and a label in it. I've broken up the code to create a box from the rest so you can use it in your programs. There are further examples of using images later in the tutorial. #include <stdlib.h> #include <gtk/gtk.h> /* Create a new hbox with an image and a label packed into it * and return the box. */ static GtkWidget *xpm_label_box( gchar *xpm_filename, gchar *label_text ) { GtkWidget *box; GtkWidget *label; GtkWidget *image; /* Create box for image and label */ box = gtk_hbox_new (FALSE, 0); gtk_container_set_border_width (GTK_CONTAINER (box), 2); /* Now on to the image stuff */ image = gtk_image_new_from_file (xpm_filename); /* Create a label for the button */ label = gtk_label_new (label_text); /* Pack the image and label into the box */ gtk_box_pack_start (GTK_BOX (box), image, FALSE, FALSE, 3); gtk_box_pack_start (GTK_BOX (box), label, FALSE, FALSE, 3); gtk_widget_show (image); gtk_widget_show (label); return box; } /* Our usual callback function */ static void callback( GtkWidget *widget, gpointer data ) { g_print ("Hello again - %s was pressed\n", (char *) data); } int main( int argc, char *argv[] ) { /* GtkWidget is the storage type for widgets */ GtkWidget *window; GtkWidget *button; GtkWidget *box; gtk_init (&argc, &argv); /* Create a new window */ window = gtk_window_new (GTK_WINDOW_TOPLEVEL); gtk_window_set_title (GTK_WINDOW (window), "Pixmap'd Buttons!"); /* It's a good idea to do this for all windows. */ g_signal_connect (G_OBJECT (window), "destroy", G_CALLBACK (gtk_main_quit), NULL); g_signal_connect (G_OBJECT (window), "delete_event", G_CALLBACK (gtk_main_quit), NULL); /* Sets the border width of the window. */ gtk_container_set_border_width (GTK_CONTAINER (window), 10); /* Create a new button */ button = gtk_button_new (); /* Connect the "clicked" signal of the button to our callback */ g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (callback), (gpointer) "cool button"); /* This calls our box creating function */ box = xpm_label_box ("info.xpm", "cool button"); /* Pack and show all our widgets */ gtk_widget_show (box); gtk_container_add (GTK_CONTAINER (button), box); gtk_widget_show (button); gtk_container_add (GTK_CONTAINER (window), button); gtk_widget_show (window); /* Rest in gtk_main and wait for the fun to begin! */ gtk_main (); return 0; } The xpm_label_box() function could be used to pack images and labels into any widget that can be a container. The Button widget has the following signals: pressed - emitted when pointer button is pressed within Button widget released - emitted when pointer button is released within Button widget clicked - emitted when pointer button is pressed and then released within Button widget enter - emitted when pointer enters Button widget leave - emitted when pointer leaves Button widget Toggle buttons are derived from normal buttons and are very similar, except they will always be in one of two states, alternated by a click. They may be depressed, and when you click again, they will pop back up. Click again, and they will pop back down. Toggle buttons are the basis for check buttons and radio buttons, as such, many of the calls used for toggle buttons are inherited by radio and check buttons. I will point these out when we come to them. Creating a new toggle button: GtkWidget *gtk_toggle_button_new( void ); GtkWidget *gtk_toggle_button_new_with_label( const gchar *label ); GtkWidget *gtk_toggle_button_new_with_mnemonic( const gchar *label ); As you can imagine, these work identically to the normal button widget calls. The first creates a blank toggle button, and the last two, a button with a label widget already packed into it. The _mnemonic() variant additionally parses the label for '_'-prefixed mnemonic characters. To retrieve the state of the toggle widget, including radio and check buttons, we use a construct as shown in our example below. This tests the state of the toggle button, by accessing the active field of the toggle widget's structure, after first using the GTK_TOGGLE_BUTTON macro to cast the widget pointer into a toggle widget pointer. The signal of interest to us emitted by toggle buttons (the toggle button, check button, and radio button widgets) is the "toggled" signal. To check the state of these buttons, set up a signal handler to catch the toggled signal, and access the structure to determine its state. The callback will look something like: void toggle_button_callback (GtkWidget *widget, gpointer data) { if (gtk_toggle_button_get_active (GTK_TOGGLE_BUTTON (widget))) { /* If control reaches here, the toggle button is down */ } else { /* If control reaches here, the toggle button is up */ } } To force the state of a toggle button, and its children, the radio and check buttons, use this function: void gtk_toggle_button_set_active( GtkToggleButton *toggle_button, gboolean is_active ); The above call can be used to set the state of the toggle button, and its children the radio and check buttons. Passing in your created button as the first argument, and a TRUE or FALSE for the second state argument to specify whether it should be down (depressed) or up (released). Default is up, or FALSE. Note that when you use the gtk_toggle_button_set_active() function, and the state is actually changed, it causes the "clicked" and "toggled" signals to be emitted from the button. gboolean gtk_toggle_button_get_active (GtkToggleButton *toggle_button); This returns the current state of the toggle button as a boolean TRUE/FALSE value. Check buttons inherit many properties and functions from the the toggle buttons above, but look a little different. Rather than being buttons with text inside them, they are small squares with the text to the right of them. These are often used for toggling options on and off in applications. The creation functions are similar to those of the normal button. GtkWidget *gtk_check_button_new( void ); GtkWidget *gtk_check_button_new_with_label ( const gchar *label ); GtkWidget *gtk_check_button_new_with_mnemonic ( const gchar *label ); The gtk_check_button_new_with_label() function creates a check button with a label beside it. Checking the state of the check button is identical to that of the toggle button. Radio buttons are similar to check buttons except they are grouped so that only one may be selected/depressed at a time. This is good for places in your application where you need to select from a short list of options. Creating a new radio button is done with one of these calls: GtkWidget *gtk_radio_button_new( GSList *group ); GtkWidget *gtk_radio_button_new_from_widget( GtkRadioButton *group ); GtkWidget *gtk_radio_button_new_with_label( GSList *group, const gchar *label ); GtkWidget* gtk_radio_button_new_with_label_from_widget( GtkRadioButton *group, const gchar *label ); GtkWidget *gtk_radio_button_new_with_mnemonic( GSList *group, const gchar *label ); GtkWidget *gtk_radio_button_new_with_mnemonic_from_widget( GtkRadioButton *group, const gchar *label ); You'll notice the extra argument to these calls. They require a group to perform their duty properly. The first call to gtk_radio_button_new() or gtk_radio_button_new_with_label() should pass NULL as the first argument. Then create a group using: GSList *gtk_radio_button_get_group( GtkRadioButton *radio_button ); The important thing to remember is that gtk_radio_button_get_group() must be called for each new button added to the group, with the previous button passed in as an argument. The result is then passed into the next call to gtk_radio_button_new() or gtk_radio_button_new_with_label(). This allows a chain of buttons to be established. The example below should make this clear. You can shorten this slightly by using the following syntax, which removes the need for a variable to hold the list of buttons: button2 = gtk_radio_button_new_with_label( gtk_radio_button_get_group (GTK_RADIO_BUTTON (button1)), "button2"); The _from_widget() variants of the creation functions allow you to shorten this further, by omitting the gtk_radio_button_get_group() call. This form is used in the example to create the third button: button2 = gtk_radio_button_new_with_label_from_widget( GTK_RADIO_BUTTON (button1), "button2"); It is also a good idea to explicitly set which button should be the default depressed button with: void gtk_toggle_button_set_active( GtkToggleButton *toggle_button, gboolean state ); This is described in the section on toggle buttons, and works in exactly the same way. Once the radio buttons are grouped together, only one of the group may be active at a time. If the user clicks on one radio button, and then on another, the first radio button will first emit a "toggled" signal (to report becoming inactive), and then the second will emit its "toggled" signal (to report becoming active). The following example creates a radio button group with three buttons. #include <glib.h> #include <gtk/gtk.h> static gboolean close_application( GtkWidget *widget, GdkEvent *event, gpointer data ) { gtk_main_quit (); return FALSE; } int main( int argc, char *argv[] ) { GtkWidget *window = NULL; GtkWidget *box1; GtkWidget *box2; GtkWidget *button; GtkWidget *separator; GSList *group; gtk_init (&argc, &argv); window = gtk_window_new (GTK_WINDOW_TOPLEVEL); g_signal_connect (G_OBJECT (window), "delete_event", G_CALLBACK (close_application), NULL); gtk_window_set_title (GTK_WINDOW (window), "radio buttons"); gtk_container_set_border_width (GTK_CONTAINER (window), 0); box1 = gtk_vbox_new (FALSE, 0); gtk_container_add (GTK_CONTAINER (window), box1); gtk_widget_show (box1); box2 = gtk_vbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0); gtk_widget_show (box2); button = gtk_radio_button_new_with_label (NULL, "button1"); gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0); gtk_widget_show (button); group = gtk_radio_button_get_group (GTK_RADIO_BUTTON (button)); button = gtk_radio_button_new_with_label (group, "button2"); gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button), TRUE); gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0); gtk_widget_show (button); button = gtk_radio_button_new_with_label_from_widget (GTK_RADIO_BUTTON (button), "button3"); gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0); gtk_widget_show (button); separator = gtk_hseparator_new (); gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 0); gtk_widget_show (separator); box2 = gtk_vbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, TRUE, 0); gtk_widget_show (box2); button = gtk_button_new_with_label ("close"); g_signal_connect_swapped (G_OBJECT (button), "clicked", G_CALLBACK (close_application), G_OBJECT (window)); gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0); GTK_WIDGET_SET_FLAGS (button, GTK_CAN_DEFAULT); gtk_widget_grab_default (button); gtk_widget_show (button); gtk_widget_show (window); gtk_main (); return 0; } GTK has various widgets that can be visually adjusted by the user using the mouse or the keyboard, such as the range widgets, described in the Range Widgets section. There are also a few widgets that display some adjustable portion of a larger area of data, such as the text widget and the viewport widget. Obviously, an application needs to be able to react to changes the user makes in range widgets. One way to do this would be to have each widget emit its own type of signal when its adjustment changes, and either pass the new value to the signal handler, or require it to look inside the widget's data structure in order to ascertain the value. But you may also want to connect the adjustments of several widgets together, so that adjusting one adjusts the others. The most obvious example of this is connecting a scrollbar to a panning viewport or a scrolling text area. If each widget has its own way of setting or getting the adjustment value, then the programmer may have to write their own signal handlers to translate between the output of one widget's signal and the "input" of another's adjustment setting function. GTK solves this problem using the Adjustment object, which is not a widget but a way for widgets to store and pass adjustment information in an abstract and flexible form. The most obvious use of Adjustment is to store the configuration parameters and values of range widgets, such as scrollbars and scale controls. However, since Adjustments are derived from Object, they have some special powers beyond those of normal data structures. Most importantly, they can emit signals, just like widgets, and these signals can be used not only to allow your program to react to user input on adjustable widgets, but also to propagate adjustment values transparently between adjustable widgets. You will see how adjustments fit in when you see the other widgets that incorporate them: Progress Bars, Viewports, Scrolled Windows, and others. Many of the widgets which use adjustment objects do so automatically, but some cases will be shown in later examples where you may need to create one yourself. You create an adjustment using: GtkObject *gtk_adjustment_new( gdouble value, gdouble lower, gdouble upper, gdouble step_increment, gdouble page_increment, gdouble page_size ); The value argument is the initial value you want to give to the adjustment, usually corresponding to the topmost or leftmost position of an adjustable widget. The lower argument specifies the lowest value which the adjustment can hold. The step_increment argument specifies the "smaller" of the two increments by which the user can change the value, while the page_increment is the "larger" one. The page_size argument usually corresponds somehow to the visible area of a panning widget. The upper argument is used to represent the bottom most or right most coordinate in a panning widget's child. Therefore it is not always the largest number that value can take, since the page_size of such widgets is usually non-zero. The adjustable widgets can be roughly divided into those which use and require specific units for these values and those which treat them as arbitrary numbers. The group which treats the values as arbitrary numbers includes the range widgets (scrollbars and scales, the progress bar widget, and the spin button widget). These widgets are all the widgets which are typically "adjusted" directly by the user with the mouse or keyboard. They will treat the lower and upper values of an adjustment as a range within which the user can manipulate the adjustment's value. By default, they will only modify the value of an adjustment. The other group includes the text widget, the viewport widget, the compound list widget, and the scrolled window widget. All of these widgets use pixel values for their adjustments. These are also all widgets which are typically "adjusted" indirectly using scrollbars. While all widgets which use adjustments can either create their own adjustments or use ones you supply, you'll generally want to let this particular category of widgets create its own adjustments. Usually, they will eventually override all the values except the value itself in whatever adjustments you give them, but the results are, in general, undefined (meaning, you'll have to read the source code to find out, and it may be different from widget to widget). Now, you're probably thinking, since text widgets and viewports insist on setting everything except the value of their adjustments, while scrollbars will only touch the adjustment's value, if you share an adjustment object between a scrollbar and a text widget, manipulating the scrollbar will automagically adjust the viewport widget? Of course it will! Just like this: /* creates its own adjustments */ viewport = gtk_viewport_new (NULL, NULL); /* uses the newly-created adjustment for the scrollbar as well */ vscrollbar = gtk_vscrollbar_new (gtk_viewport_get_vadjustment (viewport)); Ok, you say, that's nice, but what if I want to create my own handlers to respond when the user adjusts a range widget or a spin button, and how do I get at the value of the adjustment in these handlers? To answer these questions and more, let's start by taking a look at struct _GtkAdjustment itself: struct _GtkAdjustment { GtkObject parent_instance; gdouble lower; gdouble upper; gdouble value; gdouble step_increment; gdouble page_increment; gdouble page_size; }; If you don't like to poke directly at struct internals like a real C programmer, you can use the following accessor to inspect the value of an adjustment: gdouble gtk_adjustment_get_value( GtkAdjustment *adjustment); Since, when you set the value of an Adjustment, you generally want the change to be reflected by every widget that uses this adjustment, GTK provides this convenience function to do this: void gtk_adjustment_set_value( GtkAdjustment *adjustment, gdouble value ); As mentioned earlier, Adjustment is a subclass of Object just like all the various widgets, and thus it is able to emit signals. This is, of course, why updates happen automagically when you share an adjustment object between a scrollbar and another adjustable widget; all adjustable widgets connect signal handlers to their adjustment's value_changed signal, as can your program. Here's the definition of this signal in struct _GtkAdjustmentClass: void (* value_changed) (GtkAdjustment *adjustment); The various widgets that use the Adjustment object will emit this signal on an adjustment whenever they change its value. This happens both when user input causes the slider to move on a range widget, as well as when the program explicitly changes the value with gtk_adjustment_set_value(). So, for example, if you have a scale widget, and you want to change the rotation of a picture whenever its value changes, you would create a callback like this: void cb_rotate_picture (GtkAdjustment *adj, GtkWidget *picture) { set_picture_rotation (picture, gtk_adjustment_get_value (adj)); ... and connect it to the scale widget's adjustment like this: g_signal_connect (G_OBJECT (adj), "value_changed", G_CALLBACK (cb_rotate_picture), (gpointer) picture); What about when a widget reconfigures the upper or lower fields of its adjustment, such as when a user adds more text to a text widget? In this case, it emits the changed signal, which looks like this: void (* changed) (GtkAdjustment *adjustment); Range widgets typically connect a handler to this signal, which changes their appearance to reflect the change - for example, the size of the slider in a scrollbar will grow or shrink in inverse proportion to the difference between the lower and upper values of its adjustment. You probably won't ever need to attach a handler to this signal, unless you're writing a new type of range widget. However, if you change any of the values in a Adjustment directly, you should emit this signal on it to reconfigure whatever widgets are using it, like this: g_signal_emit_by_name (G_OBJECT (adjustment), "changed"); Now go forth and adjust! The category of range widgets includes the ubiquitous scrollbar widget and the less common scale widget. Though these two types of widgets are generally used for different purposes, they are quite similar in function and implementation. All range widgets share a set of common graphic elements, each of which has its own X window and receives events. They all contain a "trough" and a "slider" (what is sometimes called a "thumbwheel" in other GUI environments). Dragging the slider with the pointer moves it back and forth within the trough, while clicking in the trough advances the slider towards the location of the click, either completely, or by a designated amount, depending on which mouse button is used. As mentioned in Adjustments above, all range widgets are associated with an adjustment object, from which they calculate the length of the slider and its position within the trough. When the user manipulates the slider, the range widget will change the value of the adjustment. These are your standard, run-of-the-mill scrollbars. These should be used only for scrolling some other widget, such as a list, a text box, or a viewport (and it's generally easier to use the scrolled window widget in most cases). For other purposes, you should use scale widgets, as they are friendlier and more featureful. There are separate types for horizontal and vertical scrollbars. There really isn't much to say about these. You create them with the following functions: GtkWidget *gtk_hscrollbar_new( GtkAdjustment *adjustment ); GtkWidget *gtk_vscrollbar_new( GtkAdjustment *adjustment ); and that's about it (if you don't believe me, look in the header files!). The adjustment argument can either be a pointer to an existing Adjustment, or NULL, in which case one will be created for you. Specifying NULL might actually be useful in this case, if you wish to pass the newly-created adjustment to the constructor function of some other widget which will configure it for you, such as a text widget. Scale widgets are used to allow the user to visually select and manipulate a value within a specific range. You might want to use a scale widget, for example, to adjust the magnification level on a zoomed preview of a picture, or to control the brightness of a color, or to specify the number of minutes of inactivity before a screensaver takes over the screen. As with scrollbars, there are separate widget types for horizontal and vertical scale widgets. (Most programmers seem to favour horizontal scale widgets.) Since they work essentially the same way, there's no need to treat them separately here. The following functions create vertical and horizontal scale widgets, respectively: GtkWidget *gtk_vscale_new( GtkAdjustment *adjustment ); GtkWidget *gtk_vscale_new_with_range( gdouble min, gdouble max, gdouble step ); GtkWidget *gtk_hscale_new( GtkAdjustment *adjustment ); GtkWidget *gtk_hscale_new_with_range( gdouble min, gdouble max, gdouble step ); The adjustment argument can either be an adjustment which has already been created with gtk_adjustment_new(), or NULL, in which case, an anonymous Adjustment is created with all of its values set to 0.0 (which isn't very useful in this case). In order to avoid confusing yourself, you probably want to create your adjustment with a page_size of 0.0 so that its upper value actually corresponds to the highest value the user can select. The _new_with_range() variants take care of creating a suitable adjustment. (If you're already thoroughly confused, read the section on Adjustments again for an explanation of what exactly adjustments do and how to create and manipulate them.) Scale widgets can display their current value as a number beside the trough. The default behaviour is to show the value, but you can change this with this function: void gtk_scale_set_draw_value( GtkScale *scale, gboolean draw_value ); As you might have guessed, draw_value is either TRUE or FALSE, with predictable consequences for either one. The value displayed by a scale widget is rounded to one decimal point by default, as is the value field in its Adjustment. You can change this with: void gtk_scale_set_digits( GtkScale *scale, gint digits ); where digits is the number of decimal places you want. You can set digits to anything you like, but no more than 13 decimal places will actually be drawn on screen. Finally, the value can be drawn in different positions relative to the trough: void gtk_scale_set_value_pos( GtkScale *scale, GtkPositionType pos ); The argument pos is of type GtkPositionType, which can take one of the following values: GTK_POS_LEFT GTK_POS_RIGHT GTK_POS_TOP GTK_POS_BOTTOM If you position the value on the "side" of the trough (e.g., on the top or bottom of a horizontal scale widget), then it will follow the slider up and down the trough. All the preceding functions are defined in <gtk/gtkscale.h>. The header files for all GTK widgets are automatically included when you include <gtk/gtk.h>. But you should look over the header files of all widgets that interest you, in order to learn more about their functions and features. The Range widget class is fairly complicated internally, but, like all the "base class" widgets, most of its complexity is only interesting if you want to hack on it. Also, almost all of the functions and signals it defines are only really used in writing derived widgets. There are, however, a few useful functions that are defined in <gtk/gtkrange.h> and will work on all range widgets. The "update policy" of a range widget defines at what points during user interaction it will change the value field of its Adjustment and emit the "value_changed" signal on this Adjustment. The update policies, defined in <gtk/gtkenums.h> as type enum GtkUpdateType, are: GTK_UPDATE_CONTINUOUS This is the default. The "value_changed" signal is emitted continuously, i.e., whenever the slider is moved by even the tiniest amount. GTK_UPDATE_DISCONTINUOUS The "value_changed" signal is only emitted once the slider has stopped moving and the user has released the mouse button. GTK_UPDATE_DELAYED The "value_changed" signal is emitted when the user releases the mouse button, or if the slider stops moving for a short period of time. The update policy of a range widget can be set by casting it using the GTK_RANGE(widget) macro and passing it to this function: void gtk_range_set_update_policy( GtkRange *range, GtkUpdateType policy); Getting and setting the adjustment for a range widget "on the fly" is done, predictably, with: GtkAdjustment* gtk_range_get_adjustment( GtkRange *range ); void gtk_range_set_adjustment( GtkRange *range, GtkAdjustment *adjustment ); gtk_range_get_adjustment() returns a pointer to the adjustment to which range is connected. gtk_range_set_adjustment() does absolutely nothing if you pass it the adjustment that range is already using, regardless of whether you changed any of its fields or not. If you pass it a new Adjustment, it will unreference the old one if it exists (possibly destroying it), connect the appropriate signals to the new one, and call the private function gtk_range_adjustment_changed(), which will (or at least, is supposed to...) recalculate the size and/or position of the slider and redraw if necessary. As mentioned in the section on adjustments, if you wish to reuse the same Adjustment, when you modify its values directly, you should emit the "changed" signal on it, like this: g_signal_emit_by_name (G_OBJECT (adjustment), "changed"); All of the GTK range widgets react to mouse clicks in more or less the same way. Clicking button-1 in the trough will cause its adjustment's page_increment to be added or subtracted from its value, and the slider to be moved accordingly. Clicking mouse button-2 in the trough will jump the slider to the point at which the button was clicked. Clicking button-3 in the trough of a range or any button on a scrollbar's arrows will cause its adjustment's value to change by step_increment at a time. Scrollbars are not focusable, thus have no key bindings. The key bindings for the other range widgets (which are, of course, only active when the widget has focus) are do not differentiate between horizontal and vertical range widgets. All range widgets can be operated with the left, right, up and down arrow keys, as well as with the Page Up and Page Down keys. The arrows move the slider up and down by step_increment, while Page Up and Page Down move it by page_increment. The user can also move the slider all the way to one end or the other of the trough using the keyboard. This is done with the Home and End keys. This example is a somewhat modified version of the "range controls" test from testgtk.c. It basically puts up a window with three range widgets all connected to the same adjustment, and a couple of controls for adjusting some of the parameters mentioned above and in the section on adjustments, so you can see how they affect the way these widgets work for the user. #include <gtk/gtk.h> GtkWidget *hscale, *vscale; static void cb_pos_menu_select( GtkWidget *item, GtkPositionType pos ) { /* Set the value position on both scale widgets */ gtk_scale_set_value_pos (GTK_SCALE (hscale), pos); gtk_scale_set_value_pos (GTK_SCALE (vscale), pos); } static void cb_update_menu_select( GtkWidget *item, GtkUpdateType policy ) { /* Set the update policy for both scale widgets */ gtk_range_set_update_policy (GTK_RANGE (hscale), policy); gtk_range_set_update_policy (GTK_RANGE (vscale), policy); } static void cb_digits_scale( GtkAdjustment *adj ) { /* Set the number of decimal places to which adj->value is rounded */ gtk_scale_set_digits (GTK_SCALE (hscale), (gint) adj->value); gtk_scale_set_digits (GTK_SCALE (vscale), (gint) adj->value); } static void cb_page_size( GtkAdjustment *get, GtkAdjustment *set ) { /* Set the page size and page increment size of the sample * adjustment to the value specified by the "Page Size" scale */ set->page_size = get->value; set->page_increment = get->value; /* This sets the adjustment and makes it emit the "changed" signal to reconfigure all the widgets that are attached to this signal. */ gtk_adjustment_set_value (set, CLAMP (set->value, set->lower, (set->upper - set->page_size))); g_signal_emit_by_name(G_OBJECT(set), "changed"); } static void cb_draw_value( GtkToggleButton *button ) { /* Turn the value display on the scale widgets off or on depending * on the state of the checkbutton */ gtk_scale_set_draw_value (GTK_SCALE (hscale), button->active); gtk_scale_set_draw_value (GTK_SCALE (vscale), button->active); } /* Convenience functions */ static GtkWidget *make_menu_item ( gchar *name, GCallback callback, gpointer data ) { GtkWidget *item; item = gtk_menu_item_new_with_label (name); g_signal_connect (G_OBJECT (item), "activate", callback, (gpointer) data); gtk_widget_show (item); return item; } static void scale_set_default_values( GtkScale *scale ) { gtk_range_set_update_policy (GTK_RANGE (scale), GTK_UPDATE_CONTINUOUS); gtk_scale_set_digits (scale, 1); gtk_scale_set_value_pos (scale, GTK_POS_TOP); gtk_scale_set_draw_value (scale, TRUE); } /* makes the sample window */ static void create_range_controls( void ) { GtkWidget *window; GtkWidget *box1, *box2, *box3; GtkWidget *button; GtkWidget *scrollbar; GtkWidget *separator; GtkWidget *opt, *menu, *item; GtkWidget *label; GtkWidget *scale; GtkObject *adj1, *adj2; /* Standard window-creating stuff */ window = gtk_window_new (GTK_WINDOW_TOPLEVEL); g_signal_connect (G_OBJECT (window), "destroy", G_CALLBACK (gtk_main_quit), NULL); gtk_window_set_title (GTK_WINDOW (window), "range controls"); box1 = gtk_vbox_new (FALSE, 0); gtk_container_add (GTK_CONTAINER (window), box1); gtk_widget_show (box1); box2 = gtk_hbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0); gtk_widget_show (box2); /* value, lower, upper, step_increment, page_increment, page_size */ /* Note that the page_size value only makes a difference for * scrollbar widgets, and the highest value you'll get is actually * (upper - page_size). */ adj1 = gtk_adjustment_new (0.0, 0.0, 101.0, 0.1, 1.0, 1.0); vscale = gtk_vscale_new (GTK_ADJUSTMENT (adj1)); scale_set_default_values (GTK_SCALE (vscale)); gtk_box_pack_start (GTK_BOX (box2), vscale, TRUE, TRUE, 0); gtk_widget_show (vscale); box3 = gtk_vbox_new (FALSE, 10); gtk_box_pack_start (GTK_BOX (box2), box3, TRUE, TRUE, 0); gtk_widget_show (box3); /* Reuse the same adjustment */ hscale = gtk_hscale_new (GTK_ADJUSTMENT (adj1)); gtk_widget_set_size_request (GTK_WIDGET (hscale), 200, -1); scale_set_default_values (GTK_SCALE (hscale)); gtk_box_pack_start (GTK_BOX (box3), hscale, TRUE, TRUE, 0); gtk_widget_show (hscale); /* Reuse the same adjustment again */ scrollbar = gtk_hscrollbar_new (GTK_ADJUSTMENT (adj1)); /* Notice how this causes the scales to always be updated * continuously when the scrollbar is moved */ gtk_range_set_update_policy (GTK_RANGE (scrollbar), GTK_UPDATE_CONTINUOUS); gtk_box_pack_start (GTK_BOX (box3), scrollbar, TRUE, TRUE, 0); gtk_widget_show (scrollbar); box2 = gtk_hbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0); gtk_widget_show (box2); /* A checkbutton to control whether the value is displayed or not */ button = gtk_check_button_new_with_label("Display value on scale widgets"); gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button), TRUE); g_signal_connect (G_OBJECT (button), "toggled", G_CALLBACK (cb_draw_value), NULL); gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0); gtk_widget_show (button); box2 = gtk_hbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); /* An option menu to change the position of the value */ label = gtk_label_new ("Scale Value Position:"); gtk_box_pack_start (GTK_BOX (box2), label, FALSE, FALSE, 0); gtk_widget_show (label); opt = gtk_option_menu_new (); menu = gtk_menu_new (); item = make_menu_item ("Top", G_CALLBACK (cb_pos_menu_select), GINT_TO_POINTER (GTK_POS_TOP)); gtk_menu_shell_append (GTK_MENU_SHELL (menu), item); item = make_menu_item ("Bottom", G_CALLBACK (cb_pos_menu_select), GINT_TO_POINTER (GTK_POS_BOTTOM)); gtk_menu_shell_append (GTK_MENU_SHELL (menu), item); item = make_menu_item ("Left", G_CALLBACK (cb_pos_menu_select), GINT_TO_POINTER (GTK_POS_LEFT)); gtk_menu_shell_append (GTK_MENU_SHELL (menu), item); item = make_menu_item ("Right", G_CALLBACK (cb_pos_menu_select), GINT_TO_POINTER (GTK_POS_RIGHT)); gtk_menu_shell_append (GTK_MENU_SHELL (menu), item); gtk_option_menu_set_menu (GTK_OPTION_MENU (opt), menu); gtk_box_pack_start (GTK_BOX (box2), opt, TRUE, TRUE, 0); gtk_widget_show (opt); gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0); gtk_widget_show (box2); box2 = gtk_hbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); /* Yet another option menu, this time for the update policy of the * scale widgets */ label = gtk_label_new ("Scale Update Policy:"); gtk_box_pack_start (GTK_BOX (box2), label, FALSE, FALSE, 0); gtk_widget_show (label); opt = gtk_option_menu_new (); menu = gtk_menu_new (); item = make_menu_item ("Continuous", G_CALLBACK (cb_update_menu_select), GINT_TO_POINTER (GTK_UPDATE_CONTINUOUS)); gtk_menu_shell_append (GTK_MENU_SHELL (menu), item); item = make_menu_item ("Discontinuous", G_CALLBACK (cb_update_menu_select), GINT_TO_POINTER (GTK_UPDATE_DISCONTINUOUS)); gtk_menu_shell_append (GTK_MENU_SHELL (menu), item); item = make_menu_item ("Delayed", G_CALLBACK (cb_update_menu_select), GINT_TO_POINTER (GTK_UPDATE_DELAYED)); gtk_menu_shell_append (GTK_MENU_SHELL (menu), item); gtk_option_menu_set_menu (GTK_OPTION_MENU (opt), menu); gtk_box_pack_start (GTK_BOX (box2), opt, TRUE, TRUE, 0); gtk_widget_show (opt); gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0); gtk_widget_show (box2); box2 = gtk_hbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); /* An HScale widget for adjusting the number of digits on the * sample scales. */ label = gtk_label_new ("Scale Digits:"); gtk_box_pack_start (GTK_BOX (box2), label, FALSE, FALSE, 0); gtk_widget_show (label); adj2 = gtk_adjustment_new (1.0, 0.0, 5.0, 1.0, 1.0, 0.0); g_signal_connect (G_OBJECT (adj2), "value_changed", G_CALLBACK (cb_digits_scale), NULL); scale = gtk_hscale_new (GTK_ADJUSTMENT (adj2)); gtk_scale_set_digits (GTK_SCALE (scale), 0); gtk_box_pack_start (GTK_BOX (box2), scale, TRUE, TRUE, 0); gtk_widget_show (scale); gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0); gtk_widget_show (box2); box2 = gtk_hbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); /* And, one last HScale widget for adjusting the page size of the * scrollbar. */ label = gtk_label_new ("Scrollbar Page Size:"); gtk_box_pack_start (GTK_BOX (box2), label, FALSE, FALSE, 0); gtk_widget_show (label); adj2 = gtk_adjustment_new (1.0, 1.0, 101.0, 1.0, 1.0, 0.0); g_signal_connect (G_OBJECT (adj2), "value_changed", G_CALLBACK (cb_page_size), (gpointer) adj1); scale = gtk_hscale_new (GTK_ADJUSTMENT (adj2)); gtk_scale_set_digits (GTK_SCALE (scale), 0); gtk_box_pack_start (GTK_BOX (box2), scale, TRUE, TRUE, 0); gtk_widget_show (scale); gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0); gtk_widget_show (box2); separator = gtk_hseparator_new (); gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 0); gtk_widget_show (separator); box2 = gtk_vbox_new (FALSE, 10); gtk_container_set_border_width (GTK_CONTAINER (box2), 10); gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, TRUE, 0); gtk_widget_show (box2); button = gtk_button_new_with_label ("Quit"); g_signal_connect_swapped (G_OBJECT (button), "clicked", G_CALLBACK (gtk_main_quit), NULL); gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0); GTK_WIDGET_SET_FLAGS (button, GTK_CAN_DEFAULT); gtk_widget_grab_default (button); gtk_widget_show (button); gtk_widget_show (window); } int main( int argc, char *argv[] ) { gtk_init (&argc, &argv); create_range_controls (); gtk_main (); return 0; } You will notice that the program does not call g_signal_connect() for the "delete_event", but only for the "destroy" signal. This will still perform the desired function, because an unhandled "delete_event" will result in a "destroy" signal being given to the window. Labels are used a lot in GTK, and are relatively simple. Labels emit no signals as they do not have an associated X window. If you need to catch signals, or do clipping, place it inside a EventBox widget or a Button widget. To create a new label, use: GtkWidget *gtk_label_new( const char *str ); GtkWidget *gtk_label_new_with_mnemonic( const char *str ); The sole argument is the string you wish the label to display. To change the label's text after creation, use the function: void gtk_label_set_text( GtkLabel *label, const char *str ); The first argument is the label you created previously (cast using the GTK_LABEL() macro), and the second is the new string. The space needed for the new string will be automatically adjusted if needed. You can produce multi-line labels by putting line breaks in the label string. To retrieve the current string, use: const gchar* gtk_label_get_text( GtkLabel *label ); Do not free the returned string, as it is used internally by GTK. The label text can be justified using: void gtk_label_set_justify( GtkLabel *label, GtkJustification jtype ); Values for jtype are: GTK_JUSTIFY_LEFT GTK_JUSTIFY_RIGHT GTK_JUSTIFY_CENTER (the default) GTK_JUSTIFY_FILL The label widget is also capable of line wrapping the text automatically. This can be activated using: void gtk_label_set_line_wrap (GtkLabel *label, gboolean wrap); The wrap argument takes a TRUE or FALSE value. If you want your label underlined, then you can set a pattern on the label: void gtk_label_set_pattern (GtkLabel *label, const gchar *pattern); The pattern argument indicates how the underlining should look. It consists of a string of underscore and space characters. An underscore indicates that the corresponding character in the label should be underlined. For example, the string "__ __" would underline the first two characters and eight and ninth characters. If you simply want to have an underlined accelerator ("mnemonic") in your label, you should use gtk_label_new_with_mnemonic() or gtk_label_set_text_with_mnemonic(), not gtk_label_set_pattern(). Below is a short example to illustrate these functions. This example makes use of the Frame widget to better demonstrate the label styles. You can ignore this for now as the Frame widget is explained later on. In GTK+ 2.0, label texts can contain markup for font and other text attribute changes, and labels may be selectable (for copy-and-paste). These advanced features won't be explained here. #include <gtk/gtk.h> int main( int argc, char *argv[] ) { static GtkWidget *window = NULL; GtkWidget *hbox; GtkWidget *vbox; GtkWidget *frame; GtkWidget *label; /* Initialise GTK */ gtk_init (&argc, &argv); window = gtk_window_new (GTK_WINDOW_TOPLEVEL); g_signal_connect (G_OBJECT (window), "destroy", G_CALLBACK (gtk_main_quit), NULL); gtk_window_set_title (GTK_WINDOW (window), "Label"); vbox = gtk_vbox_new (FALSE, 5); hbox = gtk_hbox_new (FALSE, 5); gtk_container_add (GTK_CONTAINER (window), hbox); gtk_box_pack_start (GTK_BOX (hbox), vbox, FALSE, FALSE, 0); gtk_container_set_border_width (GTK_CONTAINER (window), 5); frame = gtk_frame_new ("Normal Label"); label = gtk_label_new ("This is a Normal label"); gtk_container_add (GTK_CONTAINER (frame), label); gtk_box_pack_start (GTK_BOX (vbox), frame, FALSE