Lamp

QT5
The logic is that if the timer is not running, then we start
it, else we stop it. First, give the rectangle a height, a width,
and a color. Add text to the button and anchor it to a location
on the screen. Below that, create the “flasher timer” and give
it an interval of 500ms, which is equivalent to half of a second.
The timer is then set to repeat, and an “onTriggered” callback
is created, which states “while running, toggle GPIO 200 every
half second.”
Finally, add an exit button, which is very similar to the
flasher button, but colored red and located in the bottom right.
Also, instead of toggling the timer, the exit button will close the
application. If this was a real replacement for the desktop environment,
we would shut down instead of quit. Quitting brings
you back to the LightDM screen in order to choose where to
go next.
Creating the binary
Until now, QtCreator has likely been performing a shadow
build and operating in “debug” mode. When deploying the
application, we want to build for “release”. Open a Terminal
window and navigate to the project directory. Once in the
directory, run the following commands:
$ qmake –config release blinky-ODROID.pro
$ make –j4
It should build without any issues. If you encounter errors,
download the source from http://bit.ly/1KsPX0z. After you
Figure 17 - Copying the Blink-ODROID binary to /usr/bin
build it, install it by copying the executable to the /usr/bin
directory:
$ sudo cp blinky-ODROID /usr/bin/blinky-ODROID
Testing Blinky
Testing is very easy after creating the xsession configuration
file. First, log out of the Lubuntu session with the normal logout
button. You should be back at the LightDM screen waiting
to login. At the top right, click the icon in order to open
the Desktop Environment list, and choose “Blinky”. Then, log
in with the normal ODROID/ODROID credentials. If all
went well, you should see the blinky-ODROID example appear
on the screen. This was a very simple project, but you can
use it to build very complex desktop environments. The largest
drawback is the lack of a WiFi manager and other convenient
settings dialogs.
Further reading
If you want to learn more about Qt5 or building desktop
environments, here are some links:
Desktop Environments: http://bit.ly/1MyywH5
Embedded Linux: http://bit.ly/1LMrksN
Qt5 Desktop Services: http://bit.ly/1fWjtxk
Plasma 5 Desktop Environment: http://bit.ly/1EAUtax
Figure 16 - Building the Blinky-ODROID binary
Figure 18 - Selecting the Blinky desktop environment using LightDM
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