经过资料查找，GTKFB需要依赖的东西如下：
1. ATK
2. GLIB
a) Pcre
b) Pkg-config
3. Pango
a) Freetype
b) Fontconfig
4. TIFF
5. Cairo
a) HARFBUZZ
6. Zlib
7. GDK
GTK+ for the Linux Framebuffer
Alexander Larsson
Red Hat, Inc.
alexl@redhat.com
In the upcoming GTK+2.0 release GTK+ will support rendering directly to the
framebuffer instead of using the X Window System. This is good for embedded
systems such as PDAs and other systems with very limited resources; they are
able to run without the overhead of an X server while still taking advantage
of the power of GTK+ and the large base of existing programs. This white pa-per describes how GTK+ for the Linux framebuffer works, its advantages and
limitations, how it fits into the environment, and how to obtain the software.
Table of Contents
Introduction……………………………………………………………………………………………………………2
Overview………………………………………………………………………………………………………………..2
History…………………………………………………………………………………………………………………….3
Benefits……………………………………………………………………………………………………………………3
Limitations……………………………………………………………………………………………………………..4
Memory and Storage Requirements………………………………………………………………………4
X Window System Size Comparison……………………………………………………………………..5
Does GtkFB Replace X on the Desktop?………………………………………………………………..5
Source……………………………………………………………………………………………………………………..6
Introduction
GTK+ is a graphical user interface toolkit that lets you write modern, easy to use ap-plications. It was originally written for use with the X Window System, but the 2.0
release supports several other windowing systems. The port described in this white
paper, the framebuffer port (or sometimes just GtkFB), runs without any external
windowing system. Instead, the framebuffer port runs straight on the Linux frame-buffer device.
A framebuffer is a Linux hardware device that the kernel exports to programs that
run in user space, giving those programs access to the graphics card. Having access to
the graphics card allows framebuffer device programs to change resolution/bitdepth
and read/modify the display memory of the graphics card. Most embedded Linux
ports have framebuffer device drivers for their display hardware, and there are drivers
for many standard desktop graphics cards. Both of these drivers allow this port of
GTK+ to be used on such devices.
GTK+ has traditionally used xlib to make calls over the network to an X server that
handles drawing, user input, managing overlapping windows, etc. This client-server
architecture is very nice, because it allows several programs to display on the screen
at the same time, and because the communication is over the network, they do not
even need to be run on the same computer. It is also a good way to structure a large
system, because the trusted X server contains a lot of system dependent low-level
device handling that other programs should not need to do, and shouldn’t even be
allowed to do.
The client-server architecture has some overhead though, as all communications must
be over the network, and some data is duplicated in the server and the client for per-formance reasons. Because GtkFB does not use X, it is well suited for environments
where the available memory and storage is very low and network transparency is
not needed, such as embedded devices.
Overview
GtkFB, just like GTK+, depends on a few basic libraries:
Table 1. Library Dependencies
Library Description
Glib Contains some of the basic data types
and functions needed by typical C
programs.
Pango Contains support for text and fonts in
most languages and scripts.
libpng, libjpeg, libtiff Used by the image loaders. These are
optional, and needed only if you wish to
load that particular type of image.
FreeType Additional library used by the
framebuffer port. Used to render
TrueType and Type1 fonts
GTK+ compiles to three libraries: gdk-pixbuf, gdk, and gtk. Gdk-pixbuf is a library
for loading, saving, and manipulating images; gdk is an abstraction layer for the win-dowing and graphics system; and gtk is the high-level user interface library. Almost
all framebuffer specific code is in the gdk library, which is called by the generic gtk
code, but there is some framebuffer specific code in gtk to handle managed windows.
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GTK+ for the Linux Framebuffer
The gdk library has three basic tasks: drawing graphics, handling overlapping win-dows, and generating events. At the core of gdk are the drawing primitives that let
you draw lines, polygons, text, and so forth. This is very similar to the X Window
system; in fact, a modified version of the X software rasterization library (libmi) is
used. Handling overlapping windows means keeping a tree of windows up to date
on the screen and making sure that when you draw in one window, you don’t draw
on overlapping windows. Events are generated when there is user input or when
the window system needs to tell the application something, like a window needs re-painting, or the mouse moved from one window to another. The events generated
are a subset of the ones that X generates, because gtk does not need all the events and
event-information that X gives.
When a program linked to the GtkFB libraries starts, it typically calls gtk_init() early
in the startup. At this point, GtkFB opens the Linux framebuffer device (and option-ally changes to the desired resolution and bit-depth), the keyboard, and the mouse
device. It scans a specified set of directories for fonts, and then proceeds to initialize
the window and event systems.
GtkFB has built-in drivers for the normal Linux keyboard and several normal mouse
types, including touch-screens. If other drivers are needed, it is very easy to add a
new driver. GtkFB currently doesn’t use any hardware acceleration, but support for
hardware acceleration for particular video cards could be added. Currently 8, 16, 24,
and 32 bit per pixels framebuffers are supported.
Screenshots
1
of various programs running on a 800x600 16bit framebuffer are avail-able.
History
GTK+ originally comes from theGIMPproject, where it was developed to write the
user interface. It was later split off from the project, and has since been used by many
other other programs, including the GNOME desktop project.
The much used GTK+1.2 stable release is based on X, but was ported to Win32 by
replacing the gdk library and adding some Win32 support to glib. This support was
never merged into the 1.2 release, but because the build system was changed in 2.0,
the Win32 port was included.
During the summer of 2000, Elliot Lee of Red Hat started writing the framebuffer
port of gdk. I took over the GtkFB work in October 2000 and have been working on
it since.
At the release of GTK+2.0, the framebuffer port will be a fully working port of GTK+,
with all the features of the X port.
Benefits
The main benefit with GtkFB is that you can use the powerful GTK+ library, with
its large base of software, in places where the extra size of X is not wanted, such as
PDAs and other embedded devices. The API is also exactly the same as the desktop
version, so code can easily be ported and shared between desktop and embedded
devices.
Another important benefit of GtkFB is that you are free, and even encouraged, to
modify the sourcecode of the library to better fit your needs (in terms of size and fea-tures). It is easy to trim GTK+ to fit your particular needs. Due to the LGPL License,
you need to release your changes to the library itself, but you don’t need to release
the source to your own programs.
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GTK+ for the Linux Framebuffer
GtkFB is also free of costs, licensing or otherwise, your own development costs notwith-standing.
Additionally, due to the fact that GtkFB does not use the X protocol, some old limita-tions of X have been lifted. All text is rendered anti-aliased in 256grayscales.Custom
cursors can be any color-depth, and it supports runtime screen rotation.
Limitations
Of course GtkFB has limitations too. The main limitation is the single-process model.
All code in the system must be in the same binary and run in the same process. This
means you can’t use processes to separate and protect different parts of the system
from each other. It also makes it harder to design larger systems.
Another problem is that some GTK+ programs make direct X calls when using X
features that are not supported in Gdk. These programs cannot be used with GtkFB
without change. The GNOME libraries make some direct X calls, so running GNOME
programs on the framebuffer may need some work.
X has mature and broad driver support with very good hardware acceleration. GtkFB
can support acceleration, but none is currently written, and writing acceleration code
can be difficult. This means that GtkFB can be a lot slower, especially on large screens.
Some other interesting X features are not supported by framebuffer, such as network
transparency, DGA, multiple screen and visual support, Xv extension, and Xrender
extension.
Memory and Storage Requirements
In order to evaluate the memory and storage requirement, I’ve compiled a small ver-sion of GtkFB on an x86 machine. By doing further work on compiler flags and re-moving features you are not using, you can make the binaries even smaller.
Here are the flags used to build the libraries:
glib: ./configure -enable-debug=no -disable-mem-pools
pango: ./configure -enable-debug=no -with-included-modules=yes
gtk+: ./configure -enable-debug=no -with-gdktarget=framebuffer -disable-shadowfb -disable-modules -with-included-loaders=xpm,png,jpeg
This builds both shared and static libraries. For simplicity, I’ve built xpm, png, and
jpeg image loaders into gdk-pixbuf. In a real-world case, you would probably use
dynamically loaded image loaders if you chose to use shared libraries.
The stripped, shared GtkFB libraries occupy about 2 MB of disk space. Additionally
FreeType is 202KB, libjpeg is 138KB, libpng 126KB, libz (needed by libpng) 58KB.
To give a feel for typical memory usage, I ran thetestgtkprogram (included in
the GTK+ sources) which shows various widgets. I opened three windows named
button box, buttons,andclistand then analyzed the memory requirements. Estimating
memory requirements in a virtual-memory system is a bit hard, because memory can
be dynamically paged in and out.
The RSS size (the total amount of physical memory used, not counting pages swapped
out) was 3.4MB. In Linux a page from a shared library is not written to swap but just
discarded, as it can just be read from the file when needed again. The total virtual
memory size was 6.6MB, out of which 2.3MB were shared with other processes. Of
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GTK+ for the Linux Framebuffer
the total virtual size 940KB is the mapped framebuffer, which is not actual RAM
memory.
Some further memory statistics: 72KB is the mapped Arial font, 112KB is mapped
locale info, 1444KB is mapped libc code, and 120KB is the mapped program binary.
The heap is 836KB, and the stack is 24KB.
It is interesting to compare this to a statically linked binary, because when linking
statically only the object files actually used by the program are linked into the binary.
For comparison, I compiled a version oftestgtkthat has everything linked statically
except libc (including libm).
The statically linked binary is 1.8MB, and depends on libc, libm, libdl and ld-linux
only. The RSS was slightly lower, at 2.5MB, the total virtual memory size was 5.2MB,
and 1.7MB memory was shared. The other statistics from above are the same in the
statically linked case.
Thetestgtkprogram uses a lot of widgets and GTK+ features, which means linking
it statically brings in a lot of code. To see what the size of a minimal program can be
I compiled the buttons.cexample distributed with GTK+. It just opens a window
with a button containing an image and a label. The binary is 1.3MB, RSS was at 1.9MB
and total virtual memory size 4.4MB. The heap is 376KB and the stack 20KB.
If few other programs using libc are used on the system you might want to link it
statically too. Fully statically linked binaries (including libc and libm) are 2.1MB for
testgtk(RSS 2.5MB, VM size 5.4MB) and 1.7MB for buttons.
X Window System Size Comparison
A quick comparison with the X based GTK+ is in order. I compiled an X version using
the same flags as the framebuffer version. I rantestgtk(using shared libraries) on
an Xserver that had onlytwmrunning.
Thetestgtktotal virtual memory size was 6.6MB, and the RSS was 4MB. 980KB of
mapped libraries are present that was not in the GtkFB version (X libs and thread
libs). The X version of pango is slightly larger, because it has some extra foreign lan-guage shapers. The Xserver (XFree86 4.0.1, Matrox server) total virtual memory size
is 9.2MB, not counting the mapped video ram. RSS is 7.9MB. Some of the memory is
shared withtestgtk(somewhere around 2MB). Additionally twm has a VM size of
3.2MB and a RSS of 1.6MB, but there are smaller window managers, and you might
not even need one.
The gtk and gdk-pixbuf libraries are the same size on disk, but the X gdk library
is 48KB smaller. Extra dependencies for the X version are libX11 (824KB), libXext
(51KB), and libpthread (451KB, only needed if you use threadsafe X libs). Further-more, you need an X server. The XFree86 4.0.1 one I used is 1.5 MB, not counting var-ious driver modules, but there are smaller Xservers available (tinyX is about 700KB).
The result of this simple experiment shows that framebuffer GTK+ programs are
somewhat smaller than their corresponding X versions, ignoring the size of the Xserver.
If you add an X server and a window manager the X version is a lot larger. However,
the GTK+ framebuffer port does have small window managing support which makes
it ideal for smaller devices where the overhead of X can be too much for available
memory.
Does GtkFB Replace X on the Desktop?
Many people think GtkFB will or should replace X on the desktop. This is a mis-understanding; GtkFB is not really meant to run on the desktop (except for specific
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GTK+ for the Linux Framebuffer
cases like distribution installers). For quite a few reasons outlined in the Limitations
section above, GtkFB is inferior to X on a typical desktop.
A possible cause of this thinking is the common misunderstanding that the X Win-dow System is a big, bloated, slow program that doesn’t do much good. The truth of
the matter is that X servers often look huge when you see them intop, but this is due
to the fact that they have mmap’ed the whole graphics card memory, and they keep
a lot of pixmap data that really belongs to other processes. Because X is network
independent, it can never be as efficient as an optimal non-network independent,
windowing system, but the performance loss is actually very small, and the gains are
tremendous. The current problems with X (font handling, no Anti Aliasing, bad 3D
hardware support, no video support), are currently being fixed by X extensions.
Source
Source releases of GTK+ 2.0 betas (named 1.3.x) can be found on the GTK+ FTP site
2
.
Version 1.3.2 (not released at the time of writing) will be a good release to use if you
want to try GtkFB.
In addition to glib, pango, and GTK+ you need FreeType (2.0.1 or later), which can be
found on the FreeType FTP
3
site. Optionally, to build the corresponding gdk-pixbuf
loader, you can use libjpeg, libpng, and libtiff.
GtkFB specific build documentation is ingtk+/docs/README.linux-fb.
The latest version can always be found in the GNOMECVStree. You will need to
check out and build these modules (in this order): glib, pango, and gtk+. The GNOME
Developer’s Website
4
contains a description
5
of how to check out modules from the
GNOMECVStree.
Notes
1. http://people.redhat.com/~alexl/gtkfbscreenshots.html
2. ftp://ftp.gtk.org/pub/gtk/v1.3/
3. ftp://ftp.freetype.org/pub/freetype2/
4. http://developer.gnome.org
5. http://developer.gnome.org/tools/cvs.html