path: root/doc/embclasses.doc

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** A brief guide to the Qt/Embedded internal classes
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/*!
\page emb-classes.html

\title The Qt/Embedded-specific classes

Qt/Embedded classes fall into two groups: the majority are used by
every Qt/Embedded program, and some are used only by the Qt/Embedded server. 
The Qt/Embedded server program can also be a client, as in the case of a
single-process installation. All Qt/Embedded specific source files live
in \c src/kernel and are suffixed \c{_qws}. The » symbol
indicates inheritance.

\tableofcontents

\section1 QFontManager

There is one of these per application. At application startup time it
reads the font definition file from \c $QTDIR/etc/fonts/fontdir (or \c
/usr/local/etc/qt-embedded/fonts/fontdir if QTDIR is undefined). It
keeps track of all font information and maintains a cache of rendered
fonts. It also creates the font factories: QFontManager::QFontManager
is the place to add constructors for new factories. It provides a
high-level interface for requesting a particular font and calls
QFontFactories to load fonts from disk on demand. Note that this only
applies to BDF and TrueType fonts; Qt/Embedded's optimised \c .qpf
font file format bypasses the QFontManager mechanism altogether. 

There should be no need to modify this class unless you wish to change
font matching or caching behaviour.

\section1 QDiskFont

This contains information about a single on-disk font file (e.g.
\c{/usr/local/etc/qt-embedded/times.ttf}). It holds the file path,
information about whether the font is scalable, its weight, size,
Qt/Embedded name, etc. This information is used so that QFontManager
can find the closest matching disk font (it uses a scoring mechanism
weighted towards matching names, then whether the font's italic, then
its weight). 

There should be no reason to modify this class.

\section1 QRenderedFont

There is one and only one QRenderedFont for every unique font
currently loaded by the system (that is, each unique combination of
name, size, weight, italic or not, anti-aliased or not).
QRenderedFonts are reference counted; once no one is using the
QRenderedFont it is deleted along with its cache of glyph bitmaps. The
QDiskFont it was loaded from remains opened by its QFontFactory.

There should be no reason to modify this class, unless you wish to
change the way in which glyphs are cached.


\section1 QFontFactory (and descendants QFontFactoryBDF, QFontFactoryTtf)

These provide support for particular font formats, for instance the
scalable Truetype and Type1 formats (both supported in
QFontFactoryTtf, which uses Freetype 2) and the bitmap BDF format used
by X. It's called to open an on-disk font; once a font is opened it
remains opened so that the creation of new font instances from the
disk font is fast. It can also create a QRenderedFont and convert from
Unicode values to an index into the font file. For compactness, glyphs
are stored in the order and indexes they are defined in the font
rather than in Unicode order. 

There should be no need to modify this class, but it should be
inherited if you wish to add a different type of font renderer (e.g.
for a custom vector font format).

\section1 QGlyph

This describes a particular image of a character from a QRenderedFont:
for example, the letter 'A' at 10 points in Times New Roman, bold italic,
anti-aliased. It contains pointers to a QGlyphMetrics structure with
information about the character and to the raw data for the glyph:
this is either a 1-bit mask or an 8-bit alpha channel. Each QRenderedFont
creates these on demand and caches them once created (note that this is
not currently implemented for TrueType fonts). 

You would only need to modify this class if you were, for example,
modifying Qt/Embedded to support textured fonts, in which case you
would also need to modify QGfxRaster.

\section1 QMemoryManagerPixmap/QMemoryManager

This handles requests for space for pixmaps and also keeps track of
QPF format fonts (these are small 'state dumps' of QRenderedFonts,
typically 2-20KB in size; they can be mmap'd direct from disk in order
to save memory). If a QPF font is found which matches a font request
no new QRenderedFont need be created for it. It's possible to strip out
all QFontFactory support and simply use QPFs if your font needs are modest
(for instance, if you only require a few fixed point sizes). Note that
no best-match loading is performed with QPFs, as opposed to those
loaded via QFontManager, so if you don't have the correct QPF for a point
size, text in that size will simply not be displayed. 

There should be no need to modify this class.

\section1 QScreen » QLinuxFbScreen » accelerated screens, QTransformedScreen » QVfbScreen

These encapsulate the framebuffer Qt/Embedded is drawing to, provide
support for mapping of coordinates for rotating framebuffers, allow
manipulation of the colour palette and provide access to offscreen
graphics memory for devices with separate framebuffer memories.

This is used for caching pixmaps and allowing accelerated pixmap=\>screen
blt's. QLinuxFbScreen and the accelerated screens use the Linux \c /dev/fb
interface to get access to graphics memory and information about the
characteristics of the device. The framebuffer device to open is specified
by QWS_DISPLAY. Only QTransformedScreen implements the support for rotated
framebuffers. QVfbScreen provides an X window containing an emulated
framebuffer (a chunk of shared memory is set aside as the 'framebuffer'
and blt'd into the X window): this is intended as a debugging device
allowing users to debug their applications under Qt/Embedded without leaving 
X. The accelerated screen drivers check to see if they can drive the
device specified by QWS_CARD_SLOT (which defaults to the usual position
of an AGP slot if not specified) and mmap its on-chip registers from
\c /dev/mem. They may also do chip-specific setup (initialising registers to
known values and so on). Finally, QScreen's are used to create new
QScreenCursors and QGfxes. 

If you wish to modify the way pixmaps are allocated in memory,
subclass or modify QLinuxFbScreen. If you're writing an accelerated
driver you will need to subclass QScreen or QLinuxFbScreen.

\section1 QScreenCursor » accelerated cursor » QVfbCursor

This handles drawing the on-screen mouse cursor, and saving and
restoring the screen under it for the non-accelerated cursor types.

Subclassing QScreenCursor is optional in an accelerated driver (you
would only want to do so if the hardware supports a hardware cursor).

\section1 QGfx » RasterBase » Raster » accelerated driver » QGfxVfb » QGfxTransformedRaster

This class encapsulates drawing operations, a little like a low-level
QPainter. QGfxRaster and its descendants are specifically intended
for drawing into a raw framebuffer. They can take an offset for drawing
operations and a clipping region in order to support drawing into windows.
You will need to subclass the QGfxRaster template in order to implement
an accelerated driver. 

If you're brave, modifying QGfxRaster would allow you to customise how
drawing is done or add support for a new bit depth/pixel format.

\section1 QLock, QLockHolder

This encapsulates a System V semaphore, used for synchronising access
to memory shared between Qt/Embedded clients. QLockHolder is a utility class
to make managing and destroying QLocks easier. 

There should be no need to modify this class unless porting
Qt/Embedded to an operating system without System V IPC.

\section1 QDirectPainter

This is a QPainter which also gives you a pointer to the framebuffer
of the window it's pointing to, the window's clip region and so on.
It's intended to easily allow you to do your own pixel-level manipulation
of window contents. 

There should be no reason to modify this class.

\section1 QWSSoundServer, Client

The Qt/Embedded server contains a simple sound player and mixer. Clients
can request the server play sounds specified as files. 

There should be no need to modify this class unless porting
Qt/Embedded to an operating system without a Linux-style \c /dev/dsp.

\section1 QWSWindow

This contains the server's notion of an individual top level window:
the region of the framebuffer it's allocated, the client that created it
and so forth. 

There should be no reason to modify this class.

\section1 QWSKeyboardHandler » subtypes

This handles keyboard/button input. QWSKeyboardHandler is subclassed
to provide for reading \c /dev/tty, an arbitrary low-level USB event device
(for USB keyboards) and some PDA button devices. 

Modifying QWSKeyboardHandler would allow you to support different
types of keyboard (currently only a fairly standard US PC style
keyboard is supported); subclassing it is the preferred way to handle
non-pointer input devices.

\section1 QWSMouseHandler » QWSCalibratedMouseHandler » mouse types

This handles mouse/touch-panel input. Descendants of QWSCalibratedMouseHandler
make use of filtering code which prevents 'jittering' of the pointer on
touchscreens; some embedded devices do this filtering in the kernel in
which case the driver doesn't need to inherit from QWSCalibratedMouseHandler.

Subclassing QWSCalibratedMouseHandler is preferred for touch-panels without
kernel filtering; inheriting QWSMouseHandler is the way to add any other
type of pointing device (pen tablets, touchscreens, mice, trackballs
and so forth).

\section1 QWSDisplay

This class exists only in the Qt/Embedded server and keeps track of
all the top-level windows in the system, as well as the keyboard and mouse.

You would only want to modify this if making deep and drastic
modifications to Qt/Embedded window behaviour (alpha blended windows
for example).

\section1 QWSServer 

This manages the Qt/Embedded server's Unix-domain socket connections to
clients. It sends and receives QWS protocol events and calls QWSDisplay
in order to do such things as change the allocation region of windows.

The only reason to modify this would be to use something other than
some sort of socket-like mechanism to communicate between Qt/Embedded
applications (in which case modify QWSClient too). If you have
something like Unix domain sockets, modify QWSSocket/QWSServerSocket
instead. Don't add extra QWS events to communicate between
applications, use QCOP instead.

\section1 QWSClient

This encapsulates the client side of a Qt/Embedded connection and can
marshal and demarshal events. 

There should be no reason to modify this except to use something
radically different from Unix domain sockets to communicate between
Qt/Embedded applications.

\section1 QWSDisplayData

This manages a client's QWSClient, reading and interpreting events
from the QWS server. It connects to the QWS server on application
startup, getting information about the framebuffer and creating the
memory manager. Other information about the framebuffer comes directly
from \c /dev/fb in QLinuxFbScreen. 

There should be no reason to modify this.

\section1 QWSCommands

These encapsulate the data sent to and from the QWS server. 

There should be no reason to modify them.

\section1 QCopChannel

QCop is a simple IPC mechanism for communication between Qt/Embedded
applications. String messages with optional binary data can be sent
to different channels. 

The mechanism itself is designed to be bare-bones in order for users
to build whatever mechanism they like on top of it.

\section1 QWSManager

This provides Qt/Embedded window management, drawing a title bar
and handling user requests to move, resize the window and so on.

There should be no reason to modify it but you should subclass it
if you want to modify window behaviour (point to click versus
focus follows mouse, for instance).

\section1 QWSDecoration

Descendants of this class are different styles for the Qt/Embedded
window manager, for instance QWSWindowsDecoration draws Qt/Embedded
window frames in the style of Windows CE. 

Subclass it in order to provide a new window manager appearance (the
equivalent of a Windows XP or Enlightenment theme).

\section1 QWSPropertyManager

This provides the QWS client's interface to the QWS property system
(a simpler version of the X property system, it allows you to attach
arbitrary data to top-level windows, keyed by an integer). 

There should be no reason to modify it.

\section1 QWSRegionManager

Used by both client and server to help manage top-level window regions.

There should be no reason to modify it.

\section1 QWSSocket, QWSServerSocket

Provides Unix-domain sockets. 

Modify this if you're porting to a non-Unix OS but have something
analogous to Unix-domain sockets (a byte-oriented, reliable, ordered
transmission mechanism, although you can probably implement it with
something like a message queue as well).

*/