PGPLOT(3pm)

NAME
PGPLOT - allow subroutines in the PGPLOT graphics library to be called from Perl.

SYNOPSIS
 use PGPLOT;

 pgbegin(0,"/xserve",1,1);
 pgenv(1,10,1,10,0,0);
 pglabel('X','Y','My plot');
 pgpoint(7,[2..8],[2..8],17);

 # etc...

 pgend;

DESCRIPTION
This module provides an interface to the PGPLOT graphics library. To obtain the library and its manual, see "OBTAINING PGPLOT".

For every PGPLOT function the module provides an equivalent Perl function with the same arguments. Thus the user of the module should refer to the PGPLOT manual to learn all about how to use PGPLOT and for the complete list of available functions. Note that PGPLOT is at its heart a Fortran library, so the documentation describes the Fortran interface.

Also refer to the extensive set of test scripts (t/t*.t) included in the module distribution for examples of usage of all kinds of PGPLOT routines.

How the function calls map on to Perl calls is detailed below.

  Argument Mapping - Simple Numbers And Arrays
This is more or less as you might expect - use Perl scalars and Perl arrays in place of FORTRAN/C variables and arrays.

Any FORTRAN REAL/INTEGER/CHARACTER* scalar variable maps to a Perl scalar (Perl doesn't care about the differences between strings and numbers and ints and floats).

Thus you can say:

To draw a line to point (42,$x):

 pgdraw(42,$x);

To plot 10 points with data in Perl arrays @x and @y with plot symbol no. 17. Note the Perl arrays are passed by reference:

 pgpoint(10, \@x, \@y, 17);

You can also use the old Perl4 style:

 pgpoint(10, *x, *y, 17);

but this is deprecated in Perl5.

Label the axes:

 pglabel("X axis", "Data units", $label);

Draw ONE point, see how when "N=1" pgpoint() can take a scalar as well as a array argument:

  pgpoint(1, $x, $y, 17);

  Argument Mapping - Images And 2d Arrays
Many of the PGPLOT commands (e.g. "pggray") take 2D arrays as arguments. Several schemes are provided to allow efficient use from Perl:

1.  Simply pass a reference to a 2D array, e.g:

      # Create 2D array

      $x=[];
      for($i=0; $i<128; $i++) {
         for($j=0; $j<128; $j++) {
           $$x[$i][$j] = sqrt($i*$j);
         }
      }
      pggray( $x, 128, 128, ...);

2.  Pass a reference to a 1D array:

      @x=();
      for($i=0; $i<128; $i++) {
         for($j=0; $j<128; $j++) {
           $x[$i][$j] = sqrt($i*$j);
         }
      }
      pggray( \@x, 128, 128, ...);

    Here @x is a 1D array of 1D arrays. (Confused? - see perldata(1)). Alternatively @x could be a flat 1D array with 128x128 elements, 2D routines such as pggray() etc. are programmed to do the right thing as long as the number of elements match.

3.  If your image data is packed in raw binary form into a character string you can simply pass the raw string. e.g.:

       read(IMG, $img, 32768);
       pggray($img, $xsize, $ysize, ...);

    Here the read() function reads the binary data from a file and the pggray() function displays it as a grey-scale image.

    This saves unpacking the image data in to a potentially very large 2D perl array. However the types must match. The string must be packed as a "f*" for example to use "pggray". This is intended as a short-cut for sophisticated users. Even more sophisticated users will want to download the "PDL" module which provides a wealth of functions for manipulating binary data.

    Please Note: As PGPLOT is a Fortran library it expects its images to be be stored in row order. Thus a 1D list is interpreted as a sequence of rows end to end. Perl is similar to C in that 2D arrays are arrays of pointers thus images end up stored in column order.

    Thus using perl multidimensional arrays the coordinate ($i,$j) should be stored in $img[$j][$i] for things to work as expected, e.g:

       $img = [];
       for $j (0..$nx-1) for $i (0..$ny-1) {
          $$img[$j][$i] = whatever();
       }}
       pggray($$img, $nx, $ny, ...);

    Also PGPLOT displays coordinate (0,0) at the bottom left (this is natural as the subroutine library was written by an astronomer!).

  Argument Mapping - Function Names
Some PGPLOT functions (e.g. "pgfunx") take functions as callback arguments. In Perl simply pass a subroutine reference or a name, e.g.:

 # Anonymous code reference:

 pgfunx(sub{ sqrt($_[0]) },  500, 0, 10, 0);

 # Pass by ref:

 sub foo {
   my $x=shift;
   return sin(4*$x);
 }

 pgfuny(\&foo, 360, 0, 2*$pi, 0);

 # Pass by name:

 pgfuny("foo", 360, 0, 2*$pi, 0);

  Argument Mapping - General Handling Of Binary Data
In addition to the implicit rules mentioned above PGPLOT now provides a scheme for explicitly handling binary data in all routines.

If your scalar variable (e.g. $x) holds binary data (i.e. 'packed') then simply pass PGPLOT a reference to it (e.g. "\$x"). Thus one can say:

   read(MYDATA, $wavelens, $n*4);
   read(MYDATA, $spectrum, $n*4);
   pgline($n, \$wavelens, \$spectrum);

This is very efficient as we can be sure the data never gets copied and will always be interpreted as binary.

Again see the PDL module for sophisticated manipulation of binary data, since it takes great advantage of these facilities. See in particular PDL::Graphics::PGPLOT.

Be VERY careful binary data is of the right size or your segments might get violated.

DEBUGGING
As of 2.34, there is a "PGPLOT::set_debugging" function (not exported). It takes an integer argument, and returns the previous value. When any PGPLOT function is called, if that level is >= 1, the name of the function will be printed to standard error.

HISTORY
Originally developed in the olden days of Perl4 (when it was known as 'pgperl' due to the necessity of making a special perl executable) PGPLOT is now a dynamically loadable perl module which interfaces to the FORTRAN graphics library of the same name.

OBTAINING PGPLOT
PGPLOT is a FORTRAN library with C bindings, While the Perl module uses the latter, a FORTRAN compiler is still required to build the library.

The official library and the manual are available from <http://astro.caltech.edu/~tjp/pgplot/>

Building the library using the official distribution is arcane, tedious, and error-prone. Additionally, the official distribution lacks a number of bug fixes and additions provided by the community over the years.

A modern packaging (using the GNU autotools) of the more up-to-date code base is available from <https://bitbucket.org/djerius/pgplot-autotool/downloads>

The packaging has been tested on Linux and Mac OS X.

Source code is available at either of these sites

<https://github.com/djerius/pgplot-autotool>
<https://bitbucket.org/djerius/pgplot-autotool/src>

  Cygwin
Build the pgplot library and install as above, but with these notes in mind.

Edit drivers.list to enable the drivers you wish but uncommenting desired drivers by removing the leading ! on the line. Here are the ones used by a previous PDL maintainer:

  $ grep -v '^!' drivers.list
    LXDRIV 0 /LATEX     LaTeX picture environment
    NUDRIV 0 /NULL      Null device (no output)                           Std F77
    PPDRIV 1 /PPM       Portable Pixel Map file, landscape
    PPDRIV 2 /VPPM      Portable PIxel Map file, portrait
    PSDRIV 1 /PS        PostScript printers, monochrome, landscape        Std F77
    PSDRIV 2 /VPS       Postscript printers, monochrome, portrait         Std F77
    PSDRIV 3 /CPS       PostScript printers, color, landscape             Std F77
    PSDRIV 4 /VCPS      PostScript printers, color, portrait              Std F77
    TTDRIV 5 /XTERM     XTERM Tektronix terminal emulator                 Std F77
    WDDRIV 1 /WD        X Window dump file, landscape
    WDDRIV 2 /VWD       X Window dump file, portrait
    XWDRIV 1 /XWINDOW   Workstations running X Window System              C
    XWDRIV 2 /XSERVE    Persistent window on X Window System              C

  $ vi sys_cygwin/g77_gcc.conf

  # This diff command shows the lines that need changing
  $ diff g77_gcc.conf*
  12c12
  <    XINCL="-I/usr/X11R6/include"
  ---
  >    XINCL="-I/usr/X11R6.4/include"
  48c48
  <    FFLAGD="-fno-backslash -I/usr/include"
  ---
  >    FFLAGD="-fno-backslash"
  58c58
  <    CFLAGC="-DPG_PPU -O2 -DNOMALLOCH -I. -I/usr/include"
  ---
  >    CFLAGC="-DPG_PPU -O2 -DNOMALLOCH -I."
  75c75
  <    LIBS="-L/usr/X11R6/lib -lX11 -lpng -lz"
  ---
  >    LIBS="-L/usr/X11R6.4/lib -lX11"

  $ ~/pgplot/makemake ~/pgplot cygwin
  $ make
  $ make clean
  $ make cpg
  $ PGPLOT_DIR="/usr/local/pgplot/"; export PGPLOT_DIR

Be sure to add "PGPLOT_DIR" to your environment and add it to your PATH as well.

NOTE: if problems occur, you may need to "rebaseall" your libraries.

PNG OUTPUT
If PGPLOT does not write out PNG files, check these things. First, when compiling the pgplot libraries, make sure you uncomment the PNG entries in the drivers.list file. Then when running 'make' you probably got an error like

  C<make: *** No rule to make target `png.h', needed by `pndriv.o'.  Stop.>

To fix this, find the line in the 'makefile' that starts with 'pndriv.o:' (it's near the bottom). Change, for example, ./png.h to /usr/include/png.h, if that is where your header files are (you do have the libpng and libz devel packages, don't you?). Do this for all four entries on that line, then go back and run "make".

Second, if you already have the PGPLOT Perl module and PDL installed, you probably tried to write out a PNG file and got fatal error message like:

  C<undefined symbol: png_create_write_struct>

This is because the PGPLOT Perl module does not automatically link against the png and z libraries. So when you are installing the PGPLOT Perl module (version 2.19) from CPAN, don't do "install PGPLOT", but just do "get PGPLOT". Then exit from CPAN and manually install PGPLOT, calling the makefile thusly:

  C<perl Makefile.PL EXLIB=png,z EXDIR=/usr/lib>

assuming that there exist files such as /usr/lib/libpng.so.*, /usr/lib/libz.so.*. Then do the standard "make;make test;make install;" sequence. Now you can write png files from PDL!

AUTHORS
Karl Glazebrook <kgb@aaoepp.aao.gov.au>