svgalib.faq(7) - phpMan

svgalib.faq(7) Svgalib User Manual svgalib.faq(7)

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 AT exp-math.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 con-
tains 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 con-
sole.

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 main-
tainer 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 any-
thing 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 criti-
cal background jobs on the net (servers/routers/firewalls) on low price or other-
wise even unusable hardware.

ii) X has a nice API with draw commands for any kind of 'command oriented' screen out-
put. 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 eas-
ily). 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 draw-
back 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 spe-
cial 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.