This chapter was written by Paul Schulz paul@mawsonlakes.org.
In this section we will continue to build on our previous work. We will create an analog clock application. By adding a function which periodically redraws GtkDrawingArea, the clock will be able to continuously display the time.
The application uses a compiled in ‘resource’ file, so if the GTK4 libraries and their dependencies are installed and available, the application will run from anywhere.
The program also makes use of some standard mathematical and time handling functions.
The clocks mechanics were taken from a Cairo drawing example, using gtkmm4, which can be found here.
The complete code is at the end.
The draw_clock()
function does all the work. See the
in-file comments for an explanation of how the Cairo drawing works.
For a detailed reference of what each of the Cairo functions does see the cairo_t reference.
@@@include tfc/tfc.c draw_clock @@@
In order for the clock to be drawn, the drawing function
draw_clock()
needs to be registered with GTK4. This is done
in the app_activate()
function (on line 24).
Whenever the application needs to redraw the GtkDrawingArea, it will
now call draw_clock()
.
There is still a problem though. In order to animate the clock we
need to also tell the application that the clock needs to be redrawn
every second. This process starts by registering (on the next line, line
15) a timeout function with g_timeout_add()
that will
wakeup and run another function time_handler
, every second
(or 1000ms).
@@@include tfc/tfc.c app_activate @@@
Our time_handler()
function is very simple, as it just
calls gtk_widget_queue_draw()
which schedules a redraw of
the widget.
@@@include tfc/tfc.c time_handler @@@
.. and that is all there is to it. If you compile and run the example you will get a ticking analog clock.
If you get this working, you can try modifying some of the code in
draw_clock()
to tweak the application (such as change the
color or size and length of the hands) or even add text, or create a
digital clock.
You can find the source files in the tfc
directory. it
can be compiled with ./comp tfc
.
tfc.c
@@@include tfc/tfc.c @@@
tfc.ui
@@@include tfc/tfc.ui @@@
tfc.gresource.xml
@@@include tfc/tfc.gresource.xml @@@
comp
@@@include tfc/comp @@@