Qt Reference Documentation

Qt for Embedded Linux Pointer Handling

When running a Qt for Embedded Linux application, it either runs as a server or connects to an existing server. The mouse driver is loaded by the server application when it starts running, using Qt's plugin system.

Internally in the client/server protocol, all system generated events, including pointer events, are passed to the server application which then propagates the event to the appropriate client. Note that pointer handling in Qt for Embedded Linux works for both mouse and mouse-like devices such as touch panels and trackballs.


Available Drivers

Qt for Embedded Linux provides ready-made drivers for the MouseMan, IntelliMouse, Microsoft and Linux Touch Panel protocols, for the standard Linux Input Subsystem as well as the universal touch screen library, tslib. Run the configure script to list the available drivers:

    ./configure -help

In the default Qt configuration, only the "pc" mouse driver is enabled. The various drivers can be enabled and disabled using the configure script. For example:

    configure -qt-mouse-tslib

Custom mouse drivers can be implemented by subclassing the QWSMouseHandler class and creating a mouse driver plugin (derived from the QMouseDriverPlugin class). The default implementation of the QMouseDriverFactory class will automatically detect the plugin, loading the driver into the server application at run-time.

If you are creating a driver for a device that needs calibration or noise reduction, such as a touchscreen, derive from the QWSCalibratedMouseHandler subclass instead to take advantage of its calibration functionality.

Specifying a Driver

Provided that the "pc" mouse driver is enabled, Qt for Embedded Linux will try to auto-detect the mouse device if it is one of the supported types on /dev/psaux or one of the /dev/ttyS? serial lines. If multiple mice are detected, all may be used simultaneously.

Note that Qt for Embedded Linux does not support auto-detection of touch panels in which case the driver must be specified explicitly to determine which device to use.

To manually specify which driver to use, set the QWS_MOUSE_PROTO environment variable. For example (if the current shell is bash, ksh, zsh or sh):

 export QWS_MOUSE_PROTO=<driver>[:<driver specific options>]

The valid values for the <driver> argument are MouseMan, IntelliMouse, Microsoft, LinuxTP, LinuxInput, Tslib and keys identifying custom drivers, and the driver specific options are typically a device, e.g., /dev/mouse for mouse devices and /dev/ts for touch panels.

Multiple mouse drivers can be specified in one go:

 export QWS_MOUSE_PROTO="<driver>[:<driver specific options>]
         <driver>[:<driver specific options>]
         <driver>[:<driver specific options>]"

Input will be read from all specified drivers.

The Tslib Mouse Driver
The tslib mouse driver inherits the QWSCalibratedMouseHandler class, providing calibration and noise reduction functionality in addition to generating mouse events for devices using the Universal Touch Screen Library.

To be able to compile this mouse handler, Qt for Embedded Linux must be configured with the -qt-mouse-tslib option as described above. In addition, the tslib headers and library must be present in the build environment.

The tslib sources can be downloaded from http://tslib.berlios.de. Specify the location of the library and its headers using -L and -I options in the qmake.conf file in your mkspec. Also it can be helpful to add a -rpath-link:

 QMAKE_CFLAGS += -I<path to tslib headers>
 QMAKE_LFLAGS += -L<path to tslib library> -Wl,-rpath-link=<path to tslib library>

In order to use this mouse driver, tslib must also be correctly installed on the target machine. This includes providing a ts.conf configuration file and setting the neccessary environment variables (see the README file provided with tslib for details).

The ts.conf file will usually contain the following two lines:

 module_raw input
 module linear

To make Qt for Embedded Linux explicitly choose the tslib mouse handler, set the QWS_MOUSE_PROTO environment variable as explained above.


Device Files

Make sure you are using the correct device file.

As a first step, you can test whether the device file actually gives any output. For instance, if you have specified the mouse driver with


then try examining the output from the device by entering the following command in a console:

 cat /dev/input/mouse0 | hexdump

If you see output from the device printed on the console when you move the mouse, you are probably using the correct device file; otherwise, you will need to experiment to find the correct device file.

File Permissions

Make sure you have sufficient permissions to access the device file.

The Qt for Embedded Linux server process needs at least read permission for the device file. Some drivers also require write access to the device file. For instance, if you have specified the mouse driver with


then examine the permissions of the device file by entering the following command in a console:

 ls -l /dev/input/mouse0

Change the permissions of the device file, if necessary, in the following way:

 chmod a+rw /dev/input/mouse0

If the device file is actually a symbolic link to another file, you must change the permissions of the actual file instead.