AIPS HELP file for XAS in 31DEC20
As of Sun Jul 5 20:24:42 2020
Type: XAS is the preferred TV (image display) server for AIPS.
Use: XAS is started automatically by the procedures that run on your
host machine when you start up AIPS. It uses the basic X-Windows
package to talk to the X-Window server on workstation in order to
provide the functional equivalent of a TV-display device. XAS
has eight graphics overlay planes and one to 16 (usually 16)
grey-scale channels. On most workstations it uses "24-bit" or
"true" color, in which XAS emulates the old IIS Model 70 in its
ability to show multiple images at once (including 3-color
images, hue-intensity, etc.) XAS is slower in this mode but
still plenty fast enough, so that this mode is the default.
On a few workstations, XAS must run in pseudo-color mode, using
199 grayscale levels or colors, though you can extend or reduce
this. If the workstation does not support TrueColor, XAS willl
revert to pseeudo-color, or you may request that mode with an
.Xdefaults parameter (see below). You may control the number
of gray-scale planes to some number < 16, with another of the
Unlike the older and less portable XVSS, XAS has no "button"
widgets. When AIPS and its tasks specify "press button ..", you
instead press the key corresponding to that letter, e.g. press
key "a" when asked to press "button A". You can also use the X11
function keys F3, F4, F5, and F6 for AIPS Buttons A, B, C, and D,
respectively. Keypad keys F1, F2, F3, and F4 are used by some
other computers. To switch between full-sized and a smaller
window (whose size you set with your window manager's tools),
press the F2, F7, or keypad-plus keys. There are also 2 debug
states which may be turned on and off by hitting the F8 and F9
keys. The former shows the commands coming from AIPS and
friends, while the latter shows the window-manager interupts.
Finally, pressing the ESCAPE key with the mouse cursor in the XAS
window will cause it to shut down cleanly.
XAS has the ability to tell AIPS what its window size and other
basic parameters are. In fact, XAS now keeps the image catalog
and TV parameter information inside itself. As a consequence, a
new XAS display is already initialized and TVINITs are normally
If you want to use the buffered I/O feature of XAS, you should
define an environment variable AIPS_TV_BUFFERED to be "YES". For
bash, bourne, or korh shell users this can be done thus:
AIPS_TV_BUFFERED="YES"; export AIPS_TV_BUFFERED
and for c-shell or tcsh users:
setenv AIPS_TV_BUFFERED "YES"
This should be done *before* starting the XAS TV server, and
ideally should be placed in your login (.login or .profile) file.
Using buffered I/O can considerably improve performance when the
X display is being projected across a slow link such as a modem.
In your home directory, the X-Window Manager will usually read a
file called .Xdefaults when it starts up. It can be ordered to
re-read it with the command
where refers to your home-directory .Xdefaults or to
any other appropriate file. You could put this in your login
command file if you wish to use some file other than the
default $HOME/.Xdefaults. When XAS starts, it asks the Window
Manager if the user has specified certain parameters in his
.Xdefaults or other xrdb file. They control the initial size
and placement of the window and the initial placement of its
icon. They also control the size of characters, the cursor
shape and color and the colors of the graphics channels. The
XAS part of your file might look like:
AIPStv*startIconic: 0 (set to 1 if want start as icon)
AIPStv*xPixels: 1270 (actually size of local screen-10)
AIPStv*yPixels: 924 (actually size of local screen-100)
AIPStv*charMult: 1 (or larger for big TVs)
where the names of things are obvious, the case is important, and
the values shown here are the defaults. Colors must be between 0
and 255 for the cursor and graphics channels 1 through 7.
Graphics channel 8 is used as a background and is limited to 0
through 63. The cursor shape numbers are defined in the Xlib
Reference Manual (Volume Two of The Definitive Guides to the X
Window System). Even numbers from 0 through 154 are legal, but
not all are desirable. Possibilities include 30 (a cross with 2
lines in each direction), 40 (a square with a central dot), 128
(an ellipse with a central dot), 132 (arrow like the default
cursor) and many others. 34 is a simple plus sign.
In 31DEC08, XAS has acquired more memory planes, 16 by default.
Each plane uses Xpixels times yPixels bytes, but this is
trivial in modern computers. Nonetheless, the option to
allocate fewer is available.
We have added control over the screen x and y sizes. This
means you can make them smaller than the default or bigger than
the visible screen. The latter may or may not play well with
your screen manager. The default sizes are the screen size
less 10 in x and 100 in y. The latter allows room for the top
window bar and 69 pixels minimum room to type in a window
beneath the TV.
The gamma correction is in integer 100'ths; i.e. the default 220
means a gamma correction of 2.20.
The maxGreyLevel is used only in pseudo-color visuals. The
default is the maximum for the workstation device minus 56.
XAS is able to use higher limits than this, usually the maximum
minus 18, or 237 for most workstations. The maxGreyLevel
parameter is offered because users have different numbers of
colors in what X-Windows calls the default color table. If XAS
requires more levels (colors) than are left over in the default
table it will create one of its own. Then, when the cursor
moves into the XAS window the XAS table is used for the whole
workstation and when the cursor is not in the XAS window the
default table is used for the whole workstation, including the
XAS window. This creates undesirable flashing of colors and
can even render your text windows unreadable. Using a lower
maxGreyLevel may avoid this problem, but then limits the
dynamic range of your display. These considerations do NOT
apply to TrueColor displays and a max grey level of 255 is
The use of Shared memory is important for speed when it is
available. Turn it off (value = 0) at your peril. It will be
automatically disabled if the X server and X client (XAS) are not
running on the same host, or if XAS was not built with the MIT
shared memory extension enabled (some sites don't have the
XAS has a fixed font for characters. For some applications, or
on really big TV screens, the characters may be too small.
You can make them bigger (or smaller) by setting charMult to an
integer from 1 through 5. The verb inside AIPS called CHARMULT
allows you to change sizes while running a particular XAS, but
each new XAS will start with the default character size or that
XAS now also supports the concept of asynchronous execution of
AIPS' TV commands. maxCommDelay is the maximum number of screen
update requests that can occur before the screen is updated
automatically. AIPS code usually forces this update whenever it
is needed. However, over slow links, you may wish to reduce this
to 50 or so, or even turn it off with values <= 1.
The geometry and iconGeometry code require more explanation. The
where + offsets refer to the top and left and - offsets refer to
the bottom and right. The default icon position is the top right
corner of the screen and the default window position is the top
left corner. Note that the width and height of the icon are set
by its designer and cannot be changed. They may be omitted. The
width and height set for the display window are just those which
it will take at the beginning. You may resize and move the
window, and move the icon, afterwards. As XAS starts up
iconified, it is often useful to make its iconGeometry location
somewhere other than a corner, so you don't miss it because it's
under a clock or something...
When XAS begins it asks the workstation for its dimensions and
available intensities and then tells you the parameters it will