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#### NAME

       prerex.sty  - a LaTeX document style for prerequisite charts


#### DESCRIPTION

       prerex.sty  defines  macros  that  [pdf]latex  can  use  to draw charts
consisting of labelled course boxes linked  by  arrows  that  represent
pre-   and   co-requisite  requirements.   In  addition  to  the  usual
[pdf]latex output, auxiliary files will be generated containing  image-
map data for the hyperlinked nodes in the diagram and a shell script to
crop a PNG image generated from a Postscript or PDF chart.

If the source file satisfies the constraints of the prerex(5) format, a
chart  description may be edited using the prerex(1) interactive editor
(as well as any conventional text editor).


#### TERMINOLOGY

       A prerequisite chart  consists  of  several  course  boxes,  linked  by
arrows.   Courses  are  either  half  or  full,  and may be required or
optional (or neither).  Each course  box  can  contain  a  course  code
(upper  left  corner),  a  course  title  (lower  half),  and timetable
information  (upper  right  corner).   An  arrow  can   be   either   a
prerequisite  (solid), a corequisite (dotted), or recommended (dashed).
When a conventional arrow would be inappropriate, it is possible to use
a  mini  course  "box"  (consisting of just a course code) just above a
target box.  An arbitrary line of text may be placed  anywhere  on  the
chart.


#### COORDINATE SYSTEM

       A  conventional  two-dimensional Cartesian coordinate system is used to
specify the locations of diagram elements.  The origin (where x = 0 and
y  = 0) is at the lower-left corner of the diagram.  The diagram height
is configurable; the width is determined by the  values  of  	extwidth
and  an  adjustable \unit length, which defines the absolute value of a
coordinate unit.  It is possible to put a coordinate grid with labelled
axes  in the background of a chart.  The coordinates of a box, mini, or
text-line are those of its centre point.  An arrow is described by  the
coordinates   of   the   centre   points   of  its  source  and  target
boxes/minis/text-lines.


#### USAGE

       The command \usepackage{prerex} should appear in the document preamble.
This will define a LaTeX environment

\begin{chart} ... nd{chart}

within  which  the  following  commands  may  be used to produce course
boxes, minis, text-lines, and arrows.  The order  of  commands  is  not
significant except that the commands for the source and target boxes of
an arrow should precede the command for the arrow.


#### COURSE BOXES

       The commands producing course boxes have the following forms:

\halfcourse x,y:{code}{title}{timetable}

ullcourse x,y:{code}{title}{timetable}

eqhalfcourse x,y:{code}{title}{timetable}

eqfullcourse x,y:{code}{title}{timetable}

\opthalfcourse x,y:{code}{title}{timetable}

\optfullcourse x,y:{code}{title}{timetable}

where x,y are the coordinates of the centerpoint of the  box,  relative
to  the origin of the coordinate system at the lower-left corner of the
diagram.  The code, title, and timetable arguments are arbitrary (well-
bracketed) text, possibly with LaTeX markup.

The  following  are  similar but take an additional argument to specify
the (non-default) background color of the course box:

\halfcoursec x,y:{code}{title}{timetable}{color}

ullcoursec x,y:{code}{title}{timetable}{color}

eqhalfcoursec x,y:{code}{title}{timetable}{color}

eqfullcoursec x,y:{code}{title}{timetable}{color}

\opthalfcoursec x,y:{code}{title}{timetable}{color}

\optfullcoursec x,y:{code}{title}{timetable}{color}


#### MINI COURSE BOXES AND TEXT LINES

       A mini course "box" is produced by a command of the form

\mini x,y:{code}

The following instruction  places  a  line  of  text  centered  at  the
coordinates:

ext x,y:{text-line}

There  are  several  differences  between  minis  and  text-lines.  The
maximum length allowed for a course-code may be less than  that  for  a
text-line.  A  sans-serif  font  and  a reduced font size is used for a
course-code.  A course-code may be hyperlinked but a text-line  is  not
(except when the coordinate grid is on).  A \parbox command may be used
in the text-line argument if more than one line is desired.


#### ARROWS

       Arrows between course boxes (or from a mini or text-line  to  a  course
box) are produced by commands of the form

\prereq x0,y0,x1,y1:

\coreq x0,y0,x1,y1:

ecomm x0,y0,x1,y1:

These  produce, respectively, solid, dotted, and dashed arrows from the
course box (or mini or text-line) centered at coordinates x0,y0 to  the
course box centered at coordinates x1,y1.

Arrows  by  default  have  a  non-zero  curvature (unless they are very
short).  It is  possible  to  override  the  default  curvature  for  a
particular arrow by using the instructions

\prereqc x0,y0,x1,y1;c:

\coreqc x0,y0,x1,y1;c:

ecommc x0,y0,x1,y1;c:

where  c  is  an  integer  in  the  range  0-100 specifying the desired
curvature; for example, c=0 will produce a straight  arrow.  To  change
the   default   curvature,   the   user   program   may   redefine  the
\DefaultCurvature command.


       Course boxes (including minis) may be hyperlinked.  The default URL for
course boxes is course-code.php where course-code is the code argument
of the course box. The URL scheme may be changed by  the  user  by  re-
defining the \CourseURL command.


#### COORDINATE GRID

       The  following  command produces a coordinate grid, which is useful for
editing a diagram:

\grid

The grid lines will be covered by course boxes and arrows.   The  \grid
command  also  redefines  the  \CourseURL command so that, if the mouse
cursor is placed over  a  box  or  mini  in  (some)  PDF  viewers,  the
coordinates  of  the  box,  mini,  or  text-line  will  be displayed as
follows: in the status bar in xpdf and gpdf,  and  in  a  "tooltip"  in
recent  versions  of  kpdf (now re-named okular), evince, and the Adobe
Reader.  Similarly, the coordinates of the source and target  boxes  of
arrows  are  displayed  if  the  mouse  hovers over the mid-point of an
arrow,  Such  coordinate  displays  make  it  easier  to   edit   chart
descriptions.   When  the  grid  is on, the mid-point of every arrow is
highlighted by a "bullet".

The prerex package at  http://www.ctan.org/tex-archive/graphics/prerex/
has  a patch for kpdf/okular(1) to make it display URIs in tooltips and
also capture coordinates of course boxes, arrows and background  points
in the X selection clipboard (for pasting into a command being composed
at the prerex(1) prompt).  There is also a GUI frontend  vprerex(1)  to
the  prerex(1)  editor which incorporates a minimalistic prerex-enabled
PDF viewer.


#### STAND-ALONE COMMANDS

       The following commands may be used outside a chart environment, such as
in the explanatory notes for a chart:

\solidarrow

\dottedarrow

\dashedarrow

\lightbox

\boldbox

\dashedbox


#### CONFIGURATION

       The  following  are  defined by the style file but may be re-defined by
the user:

ewcommand{\DefaultCurvature}{20}

where the argument should be in the range 0-100; 0 means no curvature.

ewcommand{\CourseURL}[3]{#3.php}

where the arguments supplied at the call are the x and y coordinates of
the box or mini and the course code.

ewcommand{\background}{LightYellow}

where LightYellow is defined by

\definecolor{LightYellow}{rgb}{1.0, 1.0, 0.878431}

\setlength{\unit}{5.7816pt}

which  defines  the  absolute size of a coordinate unit; this yields 10
pixels per coordinate unit if the chart is converted to an image at 125
dpi.

ewcommand{\dpi}{125}

ewcommand{\PixelsPerUnit}{10}

These  must  be  re-defined  together  if  the image-map data are to be
correct.

\setcounter{diagheight}{75}

which is the y-coordinate of the top of the diagram (reduced to  65  in
landscape mode); the nominal diagram width is 	extwidth / \unit + 10.

The  following define the thicknesses of the three kinds of arrows, and
the thickness of bold boxes:

ewcommand{\solidwidth}{0.5pt}

ewcommand{\dottedwidth}{0.8pt}

ewcommand{\dashedwidth}{0.5pt}

ewcommand{\boldwidth}{1.0pt}

The following command is used to change to a smaller  size  for  course
codes, timetable information, and mini-course codes:

ewcommand{\smallersize}{
elsize{-3}}

The  following  command  defines the baseline adjustment for the stand-
alone arrows and boxes; this parameter is font-dependent.



#### DEPEDENCIES

       This implementation of prerex.sty uses pgf (version 1.18 or later) with
relsize, calc, ifthen, multido, textcomp,  zref-savepos  and  hyperref.
Either  pdflatex(1)  or  latex(1)  followed  by  dvips(1) (and possibly
ps2pdf(1)) may be used.

To convert a chart to a compact but reasonably high-quality  image,  it
is suggested to use the convert(1) tool of ImageMagick(1) as follows:

convert -density 125 chart.ps chart.png

or

convert -density 125 chart.pdf chart.png

The  density parameter specifies the number of pixels per inch; if this
is too small, the image is of poor quality, and if it is too large, the
image  file  is  too  big.   By  default, the shell script generated by
prerex.sty crops the image at the southeast corner.  It is possible  to
use  a  PNG  compression  application  such as optipng(1) to reduce the
file-size of the cropped image (without loss of quality).


#### IMPLEMENTATION DETAILS

       To improve the  appearance,  boxes  are  drawn  with  slightly  rounded
corners.  The half-course boxes are assigned a minimum height to give a
more uniform appearance to horizontal rows of such boxes.  The mini and
text  boxes  have white frames and their fill colour is white, which is
assumed to be the background colour of the chart.  A text  box  is  not
normally  hyperlinked;  however,  if  the  coordinate grid is on, it is
hyperlinked and its chart coordinates are encoded in the URI.

Arrows with a small height and arrows whose source  and  target  points
have  equal  x  or  y  coordinates  are  always  draw straight (using a
specialized and simpler macro)  unless an explicit  non-zero  curvature
argument  is  provided.  If the coordinate grid is on, a hyperlink with
the source and target coordinates is placed at  the  mid-point  of  the
arrow.   A  wider  background  white  edge  is  drawn below an arrow to
improve the appearance of crossing arrows; the background also  ensures
visibility  of  the arrow when the coordinate grid is on.  A thin white
arrow (with a visible arrowhead) is drawn beneath the visible arrow  to

When  the coordinate grid is drawn, the CourseURL command is re-defined
to pass node coordinates in URIs. Also,  two  "anchor"  hyperlinks  are
inserted at the southwest and northeast corners of the diagram to allow
prerex-enabled PDF viewers to compute chart coordinates.

To support HTML versions of charts, prerex.sty generates  a  script  to
crop  a chart image at the southeast corner, allowing descriptive notes
below the chart to be treated as  ordinary  text.  Also,  it  generates
image-map data for use with an HTML image map.  To obtain absolute page
coordinates, the zsavepos, zposx and zposy commands are used; the  page
coordinates  are  converted  into  pixel  coordinates  for cropping and
image-map use.


       prerex.sty and this document may be distributed and/or  modified  under
the conditions of the LaTeX Project Public License.


#### AUTHOR

       R. D. Tennent (rdt@cs.queensu.ca)


       ImageMagick(1),  convert(1).   dvips(1),  evince(1),  gpdf(1), kpdf(1),
ps2pdf(1), tikz(1), tgf(1), vprerex(1), and xpdf(1).