\subsection{The Previewers}
texx\ is a {\em previewer} for \dvi\ files which uses the X-11 window system.
\texsun\ is a previewer for \dvi\ files which uses the SunView window system.
Both previewers allow you to
view documents on your workstation before printing them.

Everything in the following
description applies to both \texx\ and \texsun\ unless
otherwise stated.

\subsubsection{Painting}
When you start xdvi, a window will be created on your display
\footnote{
	The interaction for this varies with the window manager you're using
	and between \texx\ and \texsun.
}
and your document will be {\em painted} in that window.
The size of the window corresponds to the size of the tallest and widest
page of your document.
If your display is wide enough, the window will have two {\em leaves},
otherwise it will have a single {\em leaf}.
Each leaf will be painted with a page from your document.

texx\ takes some pains to provide the most viewable document possible.
Normally, a \TeX\ document has an inch of margin added at the left and
top margin.
If reduction of this white space allows your document to be viewed
at a large size, that margin is reduced.
If you are using \texx\ or \texsun\ to preview documents you are working
on, you may find it advantageous to specify a smaller document size
to \TeX\ or \LaTeX, allowing you to preview your document at a readable size.

\subsubsection{Shrinks}
Because most workstations do not have a screen resolution approaching that
of a laser printer,
sacrifices must be made to provide suitable fonts.

One solution would be to generate the \TeX\ fonts at your display resolution.
This requires at least two sets of fonts, one for your printer and one
for each differing screen resolution.
Another approach is to use the high-resolution fonts for the printer
and {\em shrink} them.
This is the method used by \texx\ and \texsun,
because it reduces the number of fonts
and works with a great number of display resolutions.

Fonts are shrunk using a {\em shrink factor},
which is an integer in the range of 1 to 9.
As an example, with a shrink factor of 4, a 4 by 4 set of pixels
is reduced to a single pixel on your display.
The pixel is turned on if $1/\mbox{\em blackness}$ pixels in the
original sample were turned on.
Normally, {\em blackness} is $3$, which was chosen by trial \& error,
but it can be set using the {\tt -bl} option or by setting the
{\tt Blackness} option in your defaults file.

A shrink factor of 1 is a direct view of the fonts at a normal resolution.

There are usually two goals to previewing documents.
One is to view the {\em overall structure} of the document, e.g.
to check if tables, equations and figures appear at the right spot.
Another is to check {\em detail structure}, e.g. to check
if the spacing around an equation looks right.
The interface for \texx\ provides a {\em normal shrink} and a
{\em large shrink} view of your document.
At the normal shrink size, an entire page is visible, providing an
overall view.
At the large shrink size, details are more visible.

\subsubsection{Differences Between \texx\ and \texsun}
When documents are being painted, the cursor icon for \texx\ changes to a
clock, indicating that you need to wait for the painting to finish.
For \texsun, the cursor changes to an hourglass.
When \texx\ is waiting for input, the cursor changes to a spraycan.
When \texsun\ is waiting for input, the cursor changes to a bulls-eye.

Unless the \texx\ window is {\em obscured} by another window,
the image is painted directly to the display.
If the \texx\ window is {\em obscured} by another window,
the image is painted to a {\em pixmap}, which is displayed when the
page is painted.
{\em You should only obscure the \texx\ window when the cursor is
a spraycan, not when it is a clock.}
If the window is covered or obscured while it is being painted, the
final image will not be correct.
However, if you obscure the window (e.g. overlay it with a
window for editing your document) while the spray scan is present,
the window will be correctly painted when you turn pages.
\texx\ does not take advantage of resized windows.

\texsun allows somewhat more flexibility.
Pages are painted directly to memory, and displayed when they are painted.
You can obscure the \texsun\ window at any time.
You can also enlargen the window.
While this will not change the amount of visible text for the
normal shrink size, the entire window is used to display the
large shrink size.

\subsubsection{Moving Around}
In both \texx\ and \texsun,
you move forward in your document by hitting
the {\tt RETURN} or {\tt NEWLINE} key.
If there is a single leaf, it will be erased and painted with the next page.
If there are two leaves, the right hand page will be put on the left leaf
and the left leaf will be painted with the next page.
To move backward in your document, hit the {\tt DELETE} or {\tt BACKSPACE} key.
If you type a number before hitting a key, you move forward or backward
that number of pages.

To move to a given page, type the number of the page and the ``{\tt g}''.
To quit \texx, type ``{\tt q}''.
To view a part of your document at the large shrink size,
point the cursor at the part you are interested in and hit any mouse button.
The spray can will change to a clock while the page is painted
at the larger size.
Since the entire page will not fit on the display at the larger size,
it is printed to memory, and the part you pointed to is displayed.
If your window has a single leaf, that leaf is overwritten with the
enlarged image.
In \texx,
if your window has two leaves, the enlarged image is painted on the
leaf not pointed to.
This allows you to see the overall structure and the detail at the same
time.
In \texsun, the entire window is always used.

When you release the mouse button, the page which was previously displayed
on the over written leaf is restored.
If you point to another spot {\em on the same page}, the page will not
need to be recomputed.
texx\ remembers the enlarged page as long as the normal sized page
is visible, i.e. if you turn forward several pages, and then back up,
you will need to recompute the enlarged page if you want to see the
detail view.

\subsubsection{Options}
\texx\ allows you to control the layout of the window, using either
the \texx\ command line your {\tt .XDefaults} file.
Similarly, \texsun\ allows you to control the layout of the window
using either the command line or your Sun {\tt .defaults} file.
Table \ref{table:xdvi-options} lists the available options.
Options in {\bf bold-face} apply to both \texx\ and \texsun.
Options in {\sl slant-face} apply only to \texx,
and optioned in {\it italics} apply only to \texsun.
Normally, you invoke \texx\ by simply saying {\tt xdvi yourfile}.
You invoke \texsun\ by simply saying {\tt \texsun\ yourfile}.
If ``{\tt yourfile}'' can not be found, then the suffix ``{\tt .dvi}''
is appended.
%
\begin{table}[hbt]
\centering
    \begin{tabular}{|l|c|c|p{2in}|}
	\hline
	XDefault	& Command Line & Argument Type & Meaning \\
	\hline \hline

	{\bf ReverseVideo}	& -rv
	& {\em none } & Display document in reverse video \\

	{\sl BorderWidth}	& -bw
	&  {\em integer } & Change the width of the display border. \\

	{\sl ForeGround}	& -fg
	& {\em color}	& Change the foreground display color\\ 

	{\sl BackGround}	& -bg
	& {\em color}	& Change the background display color\\ 

	{\sl HighLight}	& -hl
	& {\em color}	& Change the highlight color \\

	{\sl Border}		& -bd
	& {\em color}	& Change the border color \\

	{\sl Mouse}		& -ms
	& {\em color}	& Change the mouse color \\

	{\bf NormalShrink}	& -ns
	& {\em integer} & Change the shrink size for the overview display \\

	{\bf LargeShrink}	& -ls
	& {\em integer} & Change the shrink size for the detail display \\

	{\bf Blackness}		& -bl
	& {\em integer}	& Change the blackness threshold for shrunken fonts \\

	{\bf Leaves}		& -l
	& {\em integer} & Change the number of leaves uses (1 or 2) \\

	{\bf TopMargin}	& -tm
	& {\em float}	& Set the top margin in inches \\

	{\bf SideMargin}	& -sm
	& {\em float}	& Set the left side margin in inches \\

	{\bf Dpi}		& -dpi
	& {\em integer} & Set the desired font resolution in dots per inch \\
	\hline
    \end{tabular}
\caption{Options For \texx\ and \texsun}
\label{table:xdvi-options}
\end{table}

\subsubsection{Remembering where you were}
Currently, this section only applies to \texsun.

Since the normal use of \texsun\ involves the repeated viewing of a document
to fix formatting problems,
it would be nice to be able to return to the page you were viewing when
you left \texsun.

If you define the environment variable ``{\tt TEXSUN\_STATE}'' as the name
of a file, a {\em viewing state} will be written to that file when you
exit \texsun. 
The next time you start \texsun, this state will be added to your list of
command-line arguments before any other argument.
This allows you to override the saved state.
If the first argument is {\tt -new}, the saved state is ignored.

If you choose an absolute path name for {\tt TEXSUN\_STATE},
then you can invoke \texsun\ from a menu, but all your previewer
sessions will use the same state file.
Choosing a relative path name (e.g. ``{\tt ./.texsun-state}'') allows
you to have a state file for each different directory, but it's
difficult to convince the SunView environment to start a
tool in a given directory.