NAME
svgalib.faq - frequently asked questions about svgalib
INTRODUCTION
I (Matan Ziv-Av), added/changed some of the answers in this file, so
some answers are mine, and some are Michael’s.
List of (recently) frequently asked questions about svgalib. Esp. about
it’s status and future. Please note that as of now all answers are just
written by me, Michael Weller <eowmob@exp-math.uni-essen.de>. I’d like
this to change. So email your suggestion (best of all: question and the
answer).
Also, most questions deal with the status and future and my ideas about
it. Necessarily they contain my own private opinions on this. People
may disagree and I’m sure I don’t have the best ideas about it or may
even be completely wrong. I don’t want to force anyone to agree with
me.
Also, I was asked about MY opinions, so I’m just presenting them here.
CONTENTS
Q 1) I want to write some svgalib application. Where is the
documentation?
Q 2) My board is not supported. What now?
Q 3) I get:
You must be the owner of the current console to use svgalib.
Not running in a graphics capable console, and unable to find
one.
However, though logged in not directly from the linux console, I
am the owner of the console.
Q 4) Is svgalib dead?
Q 5) There are so many Xfree drivers, why not just use them.
Q 6) Why not just use the VGA BIOS?.
Q 7) What about GGI?
Q 8) Why not just use X11?
Q 9) Now, again, what about the future of svgalib?
Q 10) Ok, just for completeness, what are your plans about svgalib
anyway?
Q 11) Nice plan. But will it become true?
THE QUESTIONS
Q 1)
I want to write some svgalib application. Where is the documentation?
A a)
Well, did you really look at everything? The 0-README file in the top
level directory contains all function prototypes and explanations on
how to call them.
Yes, the documentation is short and/or confusing. Sorry, English is not
my native tongue. Many people complain and want to write some better
documentation. You are welcome to do so! However, up to now, either
people found the documentation sufficient once they looked at the
correct files or they just gave up. At least, I never heard from these
people again.
Also, svgalib comes with source. If in doubt: read it.
Finally: Linux distributions include svgalib, but not the source and
README’s (or hide them so good noone finds them). Well, no problem, get
full svgalib source, demos, readme’s from svgalib-*.tar.gz on any Linux
FTP server in your vicinity. Even if you don’t dare to install or
compile it, it contains the readme’s.
Oh yes, there are some simple demos in the demos/ subdir. They should
get you started.
When someone writes man(1) manual pages, a distribution might just
install them. Please do not complain, write them, mail them to me.
A b)
Finally, I, Michael Weller wrote the manpages. Looking at svgalib(7)
should get you started. Additions and corrections are still welcome, of
course.
Q 2)
My board is not supported. What now?
A)
Simple:
a) Contact the maintainers (see other README’s) and check out if
someone is working on a driver.
b) If so, contact them if you like and announce you’d be willing to
test things or even help coding.
c) If not, write a driver. Get as many docs on your card as you
can, then read and understand the internals of svgalib (again
read the README’s carefully!).
Please understand that this is a free project. I will not go and buy a
similar card and write a driver for you. I already wrote support for
the hardware I have! I just do this as a hobby. Because I don’t get
paid for this I can not just buy card & docu and spend much much time
supporting whatever graphics card on earth exists.
Also read below on the future of svgalib.
If you don’t feel able to write a driver for whatever reason, please do
not complain if other people don’t do it for you (because you are not
better than they are).
Q 3)
I get:
You must be the owner of the current console to use svgalib.
Not running in a graphics capable console, and unable to find one.
However, though logged in not directly from the linux console, I am the
owner of the console.
A)
Alas, some programs use their suid root privilege and become a full
root owned process. svgalib thinks they are run by root which does not
own the current console. Defining ROOT_VC_SHORTCUT in Makefile.cfg and
recompiling will allow svgalib to allocate a new VC. However, it will
allow any person which is able to exec that program to start in on a
new console. Even if not logged in from the console at all. Thus, for
security, you need to explicitly enable that root feature.
Q 4)
Is svgalib dead?
A)
This question comes up frequently esp. in recent times.
The answer is, of course, no.
Q 5)
There are so many Xfree drivers, why not just use them.
A)
Well, actually much of the code in there is actually already used by
svgalib. Xfree coders worked on svgalib and vice versa. But honestly,
do not expect that a driver from Xfree can just be used for svgalib.
The internal structures of Xfree and svgalib (and GGI) are just too
different. As a source of knowledge and for one or the other
subroutine, the Xfree sources are invaluable however.
Q 6)
Why not just use the VGA BIOS?.
A)
Actually, we do. There is now, thanks to Josh Vanderhoof, a VESA
driver. The VESA driver does not work on all cards, even though it
should. It does not even work on all cards where vbetest works. If
vbetest does not work it means the bios writers assumed it would always
run in DOS, and used tricks (for delay, etc.) that can’t work under
Linux. If vbetest works, but the VESA driver does not, I (Matan Ziv-Av)
believe it is due to the following reason: The driver use VESA function
4 (save/restore video state). This function can’t be used in a
singletasking environment (DOS) and as such, some bios writers failed
to implement it properly, and all the tests (which are run under DOS)
failed to discover this.
The VESA driver does work with many cards though.
Q 7)
What about GGI?
A)
Yes, GGI. Another long story. At first: Yes, I like the idea of an in
kernel graphics driver. I like it very much. And, yes, this is a bit
weird because I am the svgalib maintainer and a working GGI will make
svgalib obsolete. Again, I already said above: I did not invent svgalib
nor do I promote it as the solution (now compare this to GGI). It just
does what it does and works for me and some other people.
I liked this idea so much, I even started coding a frame buffer device
once. After a short time, other people came out with the GGI idea.
Right from their beginning they claimed to be the only source of
wisdom. I tried to join our efforts, but failed. In general we have the
same goals (read the GGI project pages for that).
Anyhow, at that time a flame war started. I don’t really know why. I
don’t see I did anything else than offering my opinions, work and
experience. But that should be judged by others.
Well, after some time I stopped bothering them. I was satisfied to
learn later though that they actually came up with some conclusions I
proposed first but weeks or months later. But let us leave the past
alone.
When intending to contribute to svgalib, you should think about what
you really want. I don’t see that GGI is becoming available soon. GGI
people told me the opposite again and again, ok, I still don’t see it.
Still out of a sudden, everything might be GGI infested, so you might
consider contributing to GGI instead.
With svgalib you might be able to use your fruits earlier. And anyone
(with supported hardware) can just use it right away without
reinstalling kernel/X11 what else (maybe being unable to use something
he did before).
Q 8)
Why not just use X11?
Yes, this is what many people say. This is the common Unix way to do
it. X does it.
But X has some drawbacks:
i) It uses many resources. Admittedly this is becoming of lesser
importance now, where you can run a sensible X11 Linux system on
8MB (16 MB for heaven like performance) which is the absolute
minimum to get a simple text editor running under M$ windows.
Still, an advantage of Linux is the ability to use old hardware
for mission critical background jobs on the net
(servers/routers/firewalls) on low price or otherwise even
unusable hardware.
ii) X has a nice API with draw commands for any kind of ’command
oriented’ screen output. I mean with that: Select a color, draw
a line, polygon, etc.
This imposes a bunch of overhead. If you just want access to the
screen memory, it slows things down as hell. If you want just to
use above’s draw commands, it is ok!
iii) One can now circumvent the API restrictions by getting direct
screen access using a special Xfree extension. Basically Xfree
just setups the screen and gives you shared memory access to the
screen memory. IMHO, this is not much different from the shared
memory X11 extension by MIT (which is probably why it was added
so easily). Still it needs quite some overhead, at least when
the card does not allow for a linear frame buffer.
However, you cannot change screen modes and rez as easily. This
is IMHO THE drawback of X. For a picture viewer, you want 256
color high/true color modes on a per picture basis (also, insert
any other application you like: movie viewers, a special game, a
drawing program). Also, you want a small picture use a low rez
s.t. it does not appear as a thumbnail, maybe use a high rez
mode for a huge picture which you don’t want to use on a
permanent basis because it flickers like hell (and you don’t
want to use a panning virtual desktop too, I hated them at
best).
This latter restriction can of course be circumvented by
enlarging the picture. But this will need much time for a
picture viewer already and certainly too much for smooth video
or game animations.
iv) Finally, the problem how X11 itself accesses the screen is not
solved. Security is usually no concern because X11 does it, is
a trusted executable and a firewall between applications and the
hardware.
Alas, there might be security holes, also the stability and
performance issues (IRQ driven accelerator queue, CPU support
for VGA memory paging) still exist, though one can expect an
Xserver to be a generally well coded application.
Q 9)
Now, again, what about the future of svgalib?
For console graphics, svgalib is still the only solution for most
people, and as such it should go on for a while. Compared to the othe
console graphics options (kgi and kernel fb device), writing svgalib
driver is the simplest (at least, this is my experience), and so it
makes sense to believe that svgalib will work on all cards where there
is someone interested enough in that support.
Q 10)
Ok, just for completeness, what are your plans about svgalib anyway?
First, make svgalib cooperate nicely with kernel fb device. Then (and
it should be very similar) make svgalib work on a secondary vga card.
A rewrite of the code for memory handling and virtual console handling
is necessary for the previous goals, but is also necessary in itself,
and so will be done also.
I do intend to maintain complete binary compatibility, so that older
programs will go on working.
As internal changes are made, the drivers have to be changed as well.
For some of the older drivers (ali, ark, ati, et3000, et4000, gvga,
oak), I no longer get any reports, so I don’t know if they still work.
Some features are also lost, for example, linear frame buffer on non-
PCI cards. This should not be a very big problem, as users with such
cards can go on using 1.3.1, as most changes are not applicable for
older machines.
SEE ALSO
svgalib(7), libvga.config(5).
AUTHOR
This file was written by Michael Weller <eowmob@exp-math.uni-essen.de>,
And later changed by Matan Ziv-Av.