XFree86 4.x tips & tricks
=========================


DGA problems
------------

Release 4.0 has DGA turned off by default.  This is true for the first
release only, with current versions this shouldn't be a problem unless
you have some old config file still in use.

You'll have turn on DGA in XF86Config, otherwise v4l-conf will not
work correctly (Modules section, extmod options).  It should work for
most cards this way, althrouth some drivers don't handle DGA correctly
in 4.0 (that's why it is off...)

If DGA doesn't work for you, you have to configure bttv by hand (or
use Xvideo, see below).  v4l-conf has the "-a" switch for this.


using Xvideo
------------

XFree86 4.0 comes with a new X11 extention for video support.  The
X-Server will handle the grabber board then, not xawtv.  This has the
advantage that the X-Server knows about the video.  Window moves can
be handled without redraw problems.  The refresh triggered by xawtv
to fix it isn't required any more.  It is possible to use the video
scalers of modern graphics boards (see below).

To use Xvideo you have to load the video4linux module into the X-Server.
Just adding 'Load "v4l"' to the Modules section of XF86Config will do.
You have to make sure xawtv is compiled on a box with with XFree86 4.0
installed.  xawtv needs the new client libraries for Xvideo support.


using hardware scaling
----------------------

Starting with XFree86 4.0.1 the Xvideo extention supports hardware-scaled
video, i.e. the video isn't written directly to the visible area of the
video memory.  Instead the bt848 hardware writes yuv data to offscreen
memory.  The graphic card's video scaler does color space conversion and
video scaling.  This way fullscreen video works in 1024x768 (and greater)
without a black border because we are not limited to the maximum size
supported by the bt848 hardware any more.

As this is very new stuff not all drivers support video scaling yet.
It basically requires the overlay functions available to the
applications via xvideo port to be exported using a X-Server internal
interface too, so other X-Server modules are able to use them.

The mga driver was the first one which supported this (matrox
G200+G400).  XFree86 4.1 adds a few more ones, a quick grep of the
source tree returns this list: ct, i810, mga, nv, savage, smi,
trident.  For ati you might want to have a look at
http://www.linuxvideo.org/gatos/.

Detailed Status:
 * mga: works, I use that myself.  On multihead cards the second head
   is not accelerated, that means hw scaling via Xvideo works on the
   first head only.
 * i810: works, according to the drivers author which asked me some
   questions about it and finally got it going.
 * tdfx: current CVS version works, next release (4.1.1) will have it.
 * nvidia: free nv driver not working correctly (4.1).  nvidia's
   binary-only works starting with release 1512.
 * others: don't know, reports welcome.

You also need a bttv version newer than 0.7.16 (the 2.2.x kernel version
is /way/ to old, kernel 2.4.x is fine).  If both bttv driver and xfree86
gfx driver support it, xfree86's video4linux driver will use hardware
scaling automagically.


drawbacks
---------

capturing images/video doesn't work if xawtv runs using the Xvideo
extention.  With the '-noxv' switch Xvideo can be disabled.


multiheaded setups
------------------

"regular" multihead with two screens works just fine.  The one only thing
you have to take care off is that you can't use the -display option to
start xawtv on the second head if you are *not* using Xvideo.  Use
"DISPLAY=:0.1 xawtv" instead.  Otherwise v4l-conf will use the wrong
screen to configure the driver.

Xvideo + xinerama works just fine starting with XFree86 4.1, older
versions show video on the first physical screen only (the one listed
first in your ServerLayout section).  Without Xvideo you'll also see
the video on the first head only.

  Gerd