tqt3/doc/charinput-qws.doc

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/*!
\page emb-charinput.html

\title Character input in Qt/Embedded

Internally in the client/server protocol, each key press and key
release is sent as a \c{QWSKeyEvent}. A QWSKeyEvent contains the
following fields:

\table
\row \i \c{unicode}
     \i Unicode value
\row \i \c{keycode}
     \i TQt keycode value as defined in \c ntqnamespace.h
\row \i \c{modifier}
     \i A bitfield consisting of some of \c TQt::ShiftButton,
	\c TQt::ControlButton, and \c TQt::AltButton.
\row \i \c{is_press}
     \i TRUE if this is a key press, FALSE if it is a key release.
\row \i \c{is_auto_repeat}
     \i TRUE if this event is caused by auto repeat.
\endtable

When the server receives a key event it is sent to each client process
which is responsible for processing the key event and sending it to
the right window, if any. Key events may come from several different
sources.

\section1 Keyboard drivers

A keyboard driver reads data from a device and gives key events to the
server.

Keyboard drivers can be compiled into the library or loaded as
plugins.  Running ./configure -help lists the available keyboard drivers.
The "tty" driver is enabled in the default configuration.

The keyboard drivers all follow the same pattern. They read keyboard
data from a device, find out which keys were pressed, and then call
the static function QWSServer::processKeyEvent() with the key information.

At present, the console keyboard driver also handles console switching
(<b>Ctrl+Alt-F1</b>...<b>Ctrl+Alt+F10</b>) and termination
(<b>Ctrl+Alt+Backspace</b>).

To add a keyboard driver for a new device, subclasses of
\c{QWSKeyboardHandler} and \c{QKbdDriverPlugin} can be
written and installed as plugins.

\section1 Key event filters (input methods)

When the server receives a key event from a keyboard driver, it first
passes it through a filter. 

This can be used to implement input methods, providing input of
characters that are not on the keyboard.

To make an input method, subclass QWSServer::KeyboardFilter (in \c
src/kernel/qwindowsystem_qws.h) and implement the virtual function \c
filter(). If \c filter() returns \c FALSE, the event will be sent to
the clients (using QWSServer::sendKeyEvent()). If \c filter() returns
\c TRUE, the event will be stopped. To generate new key events, use
QWSServer::sendKeyEvent(). (Do not use processKeyEvent(), since this
will lead to infinite recursion.)

To install a keyboard event filter, use
\c{QWSServer::setKeyboardFilter()}. Currently, only one filter
can be installed at a time.

Filtering must be done in the server process.

The launcher example contains an example of a simple input method,
\c{SimpleIM} which reads a substitution table from a file.

\section1 Pen input

Key events do not need to come from a keyboard device. The server
process may call QWSServer::sendKeyEvent() at any time. 

Typically, this is done by popping up a widget, and letting the user
specify characters with the pointer device.

<b>Note</b>: the key input widget should not take focus, since the
server would then just send the key events back to the input widget.
One way to make sure that the input widget never takes focus is to set
the \c{WStyle_Customize} and \c{WStyle_Tool} widget flags in
the TQWidget constructor.

The \link http://www.trolltech.com/products/qtopia/ Qtopia\endlink
environment contains various input widgets such as
Handwriting Recognition and Virtual Keyboard.

*/