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       prerex.sty  - a LaTeX document style for prerequisite charts


       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).


       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


       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


       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.


       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}


       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

              	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 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.


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


       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
       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.


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








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


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


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


       where LightYellow is defined by

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


       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



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


       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:





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


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



       This implementation of prerex.sty uses pgf (version 1.18 or later) with
       add-on  package  tikz.   The  following  additional  packages are used:
       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.png


              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).


       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
       obtain a thin arrowhead.

       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.


       R. D. Tennent (


       ImageMagick(1),  convert(1).   dvips(1),  evince(1),  gpdf(1), kpdf(1),
       latex(1), okular(1),  optipng(1),  pdflatex(1),  prerex(1),  prerex(5),
       ps2pdf(1), tikz(1), tgf(1), vprerex(1), and xpdf(1).

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