2.6 KiB
Periodic Events
This chapter was written by Paul Schulz paul@mawsonlakes.org.
How do we create an animation?
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.
Drawing the clock face, hour, minute and second hands
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.
The Complete code
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 @@@