Term::Gnuplot - lowlevel graphics using gnuplot drawing routines.


  use Term::Gnuplot ':ALL';
  change_term('dumb') or die "Cannot set terminal.\n";
  term_init();                          # init()
  term_start_plot();                    # graphics();
  $xmax = scaled_xmax();
  $ymax = scaled_ymax();
  put_text(h_char()*5, $ymax - v_char()*3,"Terminal Test, Perl");
  $x = $xmax/4;
  $y = $ymax/4;
  $xl = h_tic()*5;
  $yl = v_tic()*5;
  term_end_plot();                      # text();


None by default.

Exportable and export tags:

  change_term test_term init_terminal list_terms  plot_outfile_set
  term_init term_start_plot term_end_plot
  term_start_multiplot term_end_multiplot plotsizes_scale
  name description xmax ymax v_char h_char v_tic h_tic
  scaled_xmax scaled_ymax
  init scale graphics linetype move vector point text_angle
  justify_text put_text arrow text clear_box pattern_fill_box color_fill_box
  fillbox make_gray_palette set_color previous_palette
  filled_polygon put_right_justified_text
  put_centered_text put_left_justified_text

Hash of name => description pairs. In particular, keys %description contains names of supported terminals.


All of the above.


Below I include the contents of the file term/README from gnuplot distribution (see "gnuplot term/README"). It explains the meaning of the methods of "SYNOPSIS".

All methods are supported under Perl, the options method is available as set_options(). The discription below includes underscores, that are deleted in the perl interface.

The functions which are not included in the description below:




Print names/descriptions of supported terminals.


Returns a hash reference with descriptions of supported terminals indexed by their names (for testing purposes only; tests redir-output of list_terms()).


set the output file. This should be done before setting the terminal type.

plotsizes_scale($xfactor, $yfactor)

set the size of the output device (such as a graphic file) in fractions of the default size. Some output drivers may ignore this request. The request is active until the next request.

Does not change sizes reported by xmax() and ymax()! After such a call one should use the following calls:

scaled_xmax(), scaled_ymax()

Report xmax() and ymax() corrected by the scaling factors given to plotsizes_scale().

term_init(), term_start_plot(), term_end_plot()

higher-level functions variants of init(), graphics(), text(). Should be prefered over init(), graphics(), text() if the output file is changed, since they take into account resetting of output file mode (if needed).

term_start_multiplot(), term_end_multiplot()

Interfaces to C functions with the same names. How to use them outside of gnuplot proper is not clear.


Returns hash of names/descriptions of supported terminals (available as %Term::Gnuplot::description too).


Sets the Tk widget for direct-draw operations (may be used with terminal 'tkcanvas' with the option 'tkperl_canvas').

clear_box($xleft, $ybottom, $width, $height)

Clears a rectangle to the background color. May die() if not implemented.

On some terminals this may reset fill color to the background color; better call linetype() again after this call.

pattern_fill_box($pattern, $xleft, $ybottom, $width, $height)

Fills box; $pattern is a small plot-terminal dependent integer. For many terminals linetype() means color; then the current color is used as the foreground color.

color_fill_box($intensity, $xleft, $ybottom, $width, $height)

Fills box with a half-tone color; $intensity changes between 0 and 1. The corresponding solid color is as above.


Should be called before any filled-rectangle operation is called


$color is a floating point number between 0 and 1. Currently only gray-scale palette is supported, so the semantic of this number is the brightness.


does not make a lot of sense until user-settable palettes are present.


takes a list of integers describing x- and y- coordinates of the vertices of a polygon (x and y alternating). Uses the color set by set_color().

put_right_justified_text(), put_centered_text(), put_left_justified_text()

Same as put_text(), but provide terminal-independent justification too. The setting of justification is preserved.

May be used in presence of text rotation too..

NOTE. Some terminals require calling set_options() before init()! Similarly, in some situation it is required to call linewidth() and linetype() at the start of plot.

gnuplot term/README


By Russell Lang 1/90

Updated for new file layout by drd 4/95

Paragraphs about inclusion of TERM_HELP added by rcc 1/96

No change to the interface between gnuplot and the terminal drivers, but we would like to make the terminal drivers standalone

1) in order move the support for the terminal drivers outside of the support for the main program, thereby encouraging a library of contributed drivers 2) To make it easy for users to add contributed drivers, by adding a single #include line to term.h 3) To allow individual compilation on DOS, to save the overlay manager from having to load _all_ drivers together.

CORRECTION - scale() interface is no longer supported, since it is incompatible with multiplot.

Whole of terminal driver should be contained in one <driver>.trm file, with a fairly strict layout as detailed below - this allows the gnuplot maintainers to change the way the terminal drivers are compiled without having to change the drivers themselves.

term.h, and therefore each file.trm file, may be loaded more than once, with different sections selected by macros.

Each driver provides all the functions it needs, and a table of function pointers and other data to interface to gnuplot. The table entry is currently defined as follows in plot.h:

  struct TERMENTRY {

  /* required entries */

        char *name;
        char *description;
        unsigned int xmax,ymax,v_char,h_char,v_tic,h_tic;

        void (*options) __PROTO((void));
        void (*init) __PROTO((void));
        void (*reset) __PROTO((void));
        void (*text) __PROTO((void));
        int (*scale) __PROTO((double, double));
        void (*graphics) __PROTO((void));
        void (*move) __PROTO((unsigned int, unsigned int));
        void (*vector) __PROTO((unsigned int, unsigned int));
        void (*linetype) __PROTO((int));
        void (*put_text) __PROTO((unsigned int, unsigned int,char*));

  /* optional entries */

        int (*text_angle) __PROTO((int));
        int (*justify_text) __PROTO((enum JUSTIFY));
        void (*point) __PROTO((unsigned int, unsigned int,int));
        void (*arrow) __PROTO((unsigned int, unsigned int, unsigned int,
                           unsigned int, int));
   int (*set_font) __PROTO((char *font));  /* "font,size" */
        void (*set_pointsize) __PROTO((double size)); /* notification of set pointsize */
        int flags; /* various flags */
   void (*suspend) __PROTO((void)); /* after one plot of multiplot */
   void (*resume) __PROTO((void));  /* before subsequent plot of multiplot */
   void (*boxfill) __PROTO((int style, unsigned int x1, unsigned int y1, unsigned int width, unsigned int height)); /* clear part of multiplot */
   void (*linewidth) __PROTO((double linewidth));
   void (*pointsize) __PROTO((double pointsize));

One consequence of (1) is that we would like drivers to be backwards compatible - drivers in the correct form below should work in future versions of gnuplot without change. C compilers guarantee to fill unitialised members of a structure to zero, so gnuplot can detect old drivers, in which fields have not been initalised, and can point new interface entry pointers to dummy functions.

We can add fields to the terminal structure, but only at the end of the list. If you design a terminal that cant work without a new interface being defined, and consequent changes to the main gnuplot source, please contact simply to ensure that you have the most up to date defn of the terminal structure. Also, please ensure that the 'set term' command checks for 0 values in added fields when an old driver is selected, and a pointer to a suitable 'cant do' function is provided. It is therefore not required (and in fact not possible) to add padding fields to the end of all drivers.

Similarly, if you add an optional field to an old driver, take care to ensure that all intervening fields are padded with zeros.

Some of the above fields are required - this should not be a problem, since they were all required in earlier releases of gnuplot. The later fields are interfaces to capabilities that not all devices can do, or for which the generic routines provided should be adequate. There are several null ('cant do') functions provided by term.c which a driver can reference in the table. Similarly, for bitmap devices, there are generic routines for lines and text provided by bitmap.c

Here's a brief description of each variable:

The char *name is a pointer to a string containing the name of the terminal. This name is used by the 'set terminal' and 'show terminal' commands. The name must be unique and must not be confused with an abbreviation of another name. For example if the name "postscript" exists, it is not possible to have another name "postscript2". Keep the name under 15 characters.

The char *description is a pointer to a string containing a description of the terminal, which is displayed in response to the 'set terminal' command. Keep the description under 60 characters.

xmax is the maximum number of points in the x direction. The range of points used by gnuplot is 0 to xmax-1.

ymax is the maximum number of points in the y direction. The range of points used by gnuplot is 0 to ymax-1.

v_char is the height of characters, in the same units as xmax and ymax. The border for labelling at the top and bottom of the plot is calculated using v_char. v_char is used as the vertical line spacing for characters.

h_char is the width of characters, in the same units as xmax and ymax. The border for labelling at the left and right of the plot is calculated using h_char, for example. If the _justify_text function returns FALSE, h_char is used to justify text right or centre. If characters are not fixed width, then the _justify_text function must correctly justify the text.

v_tic is the vertical size of tics along the x axis, in the same units as ymax.

h_tic is the horizontal size of tics along the y axis, in the same units as xmax.

v_tic and h_tic should give tics of the same physical size on the output. The ratio of these two quantities is used by gnuplot to set the aspect ratio to 1 so that circles appear circular when 'set size square' is active.

All the above values need not be static - values can be substituted into the table during terminal initialisation, based on options for example.

Here's a brief description of what each term.c function does:

_options() Called when terminal type is selected. This procedure should parse options on the command line. A list of the currently selected options should be stored in term_options[] in a form suitable for use with the set term command. term_options[] is used by the save command. Use options_null() if no options are available.

_init() Called once, when the device is first selected. This procedure should set up things that only need to be set once, like handshaking and character sets etc... There is a global variable 'pointsize' which you might want to use here. If set pointsize is issued after init has been called, the set_pointsize() function is called.

_reset() Called when gnuplot is exited, the output device changed or the terminal type changed. This procedure should reset the device, possibly flushing a buffer somewhere or generating a form feed.

_scale(xs,ys) Called just before _graphics(). This takes the x and y scaling factors as information. If the terminal would like to do its own scaling, it returns TRUE. Otherwise, it can ignore the information and return FALSE: do_plot will do the scaling for you. null_scale is provided to do just this, so most drivers can ignore this function entirely. The Latex driver is currently the only one providing its own scaling. PLEASE DO NOT USE THIS INTERFACE - IT IS NOT COMPATIBLE WITH MULTIPLOT.

_graphics() Called just before a plot is going to be displayed. This procedure should set the device into graphics mode. Devices which can't be used as terminals (like plotters) will probably be in graphics mode always and therefore won't need this.

_text() Called immediately after a plot is displayed. This procedure should set the device back into text mode if it is also a terminal, so that commands can be seen as they're typed. Again, this will probably do nothing if the device can't be used as a terminal. This call can be used to trigger conversion and output for bitmap devices.

_move(x,y) Called at the start of a line. The cursor should move to the (x,y) position without drawing.

_vector(x,y) Called when a line is to be drawn. This should display a line from the last (x,y) position given by _move() or _vector() to this new (x,y) position.

_linetype(lt) Called to set the line type before text is displayed or line(s) plotted. This procedure should select a pen color or line style if the device has these capabilities. lt is an integer from -2 to 0 or greater. An lt of -2 is used for the border of the plot. An lt of -1 is used for the X and Y axes. lt 0 and upwards are used for plots 0 and upwards. If _linetype() is called with lt greater than the available line types, it should map it to one of the available line types. Most drivers provide 9 different linetypes (lt is 0 to 8).

_put_text(x,y,str) Called to display text at the (x,y) position, while in graphics mode. The text should be vertically (with respect to the text) justified about (x,y). The text is rotated according to _text_angle and then horizontally (with respect to the text) justified according to _justify_text.

The following are optional

_text_angle(ang) Called to rotate the text angle when placing the y label. If ang = 0 then text is horizontal. If ang = 1 then text is vertically upwards. Returns TRUE if text can be rotated, FALSE otherwise. [But you must return TRUE if called with ang=0]

_justify_text(mode) Called to justify text left, right or centre. If mode = LEFT then text placed by _put_text is flushed left against (x,y). If mode = CENTRE then centre of text is at (x,y). If mode = RIGHT then text is placed flushed right against (x,y). Returns TRUE if text can be justified Returns FALSE otherwise and then _put_text assumes text is flushed left; justification of text is then performed by calculating the text width using strlen(text) * h_char.

_point(x,y,point) Called to place a point at position (x,y). point is -1 or an integer from 0 upwards. At least 6 point types (numbered 0 to 5) are normally provided. Point type -1 is a dot. If point is more than the available point types then it should be mapped back to one of the available points. Two _point() functions called do_point() and line_and_point() are provided in term.c and should be suitable for most drivers. do_point() draws the points in the current line type. If your driver uses dotted line types (generally because it is monochrome), you should use line_and_point() which changes to line type 0 before drawing the point. line type 0 should be solid.

There is a global variable 'pointsize' which is controlled by the set pointsize command. If possible, use that. pointsize should be examined at terminal init. If it is subsequently changed, the set_pointsize() fn will be called.

_arrow(sx,sy,ex,ey,head) Called to draw an arrrow from (sx,sy) to (ex,ey). A head is drawn on the arrow if head = TRUE. An _arrow() function called do_arrow() is provided in term.c which will draw arrows using the _move() and _vector() functions. Drivers should use do_arrow unless it causes problems.

_set_font() is called to set the font of labels, etc [new 3.7 feature] fonts are selected as strings "name,size"

_pointsize() is used to set the pointsize for subsequent points

_flags stores various flags describing driver capabilities. Currently three bits are allocated - TERM_CAN_MULTIPLOT - driver can do multiplot fully-interactively when output is not redirected. ie text and graphics go to different places, or driver can flip using suspend. - TERM_CANT_MULTIPLOT - driver cannot multiplot, even if output is redirected. - TERM_BINARY - output file must be opened in binary mode Another bit is earmarked for VMS_PASTHRU, but not yet implemented.

_suspend() - called before gnuplot issues a prompt in multiplot mode linux vga driver uses this entry point to flip from graphics to text mode. X11 driver will take this opportunity to paint the window on the display.

_resume() - called after suspend(), before subsequent plots of a multiplot.

_boxfill() - fills a box in given style (currently unimplemented - always background colour at present). used by 'clear' in multiplot for support of inset graphs

_linewidth() - sets the linewidth

The following should illustrate the order in which calls to these routines are made:




A file bitmap.c is provided, implementing a generic set of bitmap routines. It provides all the routines required to generate a bitmap in memory, drawing lines and writing text. A simple driver need provide only a text() entry point, which converts and outputs the stored bitmap in the format required by the device.

Internally, the bitmap is built of one or more planes of 1 bit per pixel. In fact, I think the library would be easier to use if it offered one or more planes of pixels with 1,2,4 or 8 bits per pixel, since not all bitmap devices are based on planes, and the planes have to be recombined at the end at present. In general, a device would use either planes or bits-per-pixel, though I guess a 24-bit bitmap could use 3 planes of 8 bits per pixel..?

The pixels are currently organised horizontally packed into bytes.


  ********%%%%%%%%$$$$$$$$!!!!!!!! etc
  ^^^^^^^^@@@@@@@@########++++++++ etc

where like symbols are stored in one byte. Vertical packing can be arranged by reversing x and y dimensions and setting the global b_rastermode to TRUE. (eg epson 8-pin dot-matrix printer)

Functions provided are

(internal fns ? - should probably be static, not external ?)


setting up stuff

  b_makebitmap(x,y,planes)  - make a bitmap of size x * y
  b_freebitmap()            - free bitmap

gnuplot driver interface functions (can go straight into gnuplot structure)


I think that the library could be made easier to use if we defined a structure which described the bitmap (raster mode, planes, bits-per-pixel, colours, etc) and then added to the gnuplot term struct a pointer to this structure. Then we could have b_graphics() routine which did all the initialisation that presently has to be done by the driver graphics() entry point. Also, one day I would like to have parsing, including terminal driver options, table-driven, but I'm getting ahead of myself here.

At present, bitmap.c is linked into gnuplot unconditionally. Perhaps it should be put into a library, so that it is linked in only if any of the user-selected drivers require bitmap support.

There may be scope to do similar things with some of the other stuff that is shared by several drivers. Rather than requiring, for example, that LATEX driver is required if EMTEX is to be used, the shared routines could be extracted to a library and linked if any of the drivers which use them are used. Just a thought...


FILE LAYOUT -----------

I think a file layout like the following will leave most flexibility to the gnuplot maintainers. I use REGIS for example.

  #include "driver.h"

  register_term(regis) /* no ; */

  #ifdef TERM_PROTO
  TERM_PUBLIC void REGISinit __PROTO((void));
  TERM_PUBLIC void REGISgraphics __PROTO((void));
  /* etc */

  #ifdef TERM_BODY

  TERM_PUBLIC void REGISinit()
    /* etc */

  /* etc */


  #ifdef TERM_TABLE

    /* no { */
    "regis", "REGIS graphics language",
    REGISXMAX, /* etc */
    /* no } */

  #undef LAST_TERM
  #define LAST_TERM regis_driver

  #endif /* TERM_TABLE */
  #endif /* TERM_PROTO_ONLY */

  #ifdef TERM_HELP
  "1 regis",
  "?set terminal regis",
  " The `regis` terminal device generates output in the REGIS graphics language.",
  " It has the option of using 4 (the default) or 16 colors.",
  " Syntax:",
  "         set term regis {4 | 16}"


The first three lines in the TERM_HELP section must contain the same name as that specified by register_term, since this is the name that will be entered into the list of available terminals. If more than one name is registered, the additional names should have their own two "?" lines, but not the "1" line.

Each record is enclosed in double-quotes and (except for the last record) followed by a comma. The text is copied as a single string into gnuplot.doc, so the syntax must obey the rules of that entity. If the text includes double-quotes or backslashes, these must be escaped by preceding each occurence with a backslash.



We may want to compile all drivers into term.c or one driver at a time this layout should support both TERM_PUBLIC will be static if all modules are in term.c, or blank otherwise. Please make private support functions static if possible.

We may include term.h, and therefore all these files, one or more times. If just once (all modules compiled into term.c) putting the four parts in this order should make it work.

we may compile the table entries into either an array or a linked list This organisation should support both

For separate compilation, we may write a program which defines TERM_REGISTER and #include term.h to find out which drivers are selected in term.h and thereby generate a makefile.

For a driver which depends on another (eg enhpost and pslatex on post) the driver can do something like

  #ifndef GOT_POST_PROTO
  #include "post.trm"

this is probably needed only in the TERM_TABLE section only, but may also be used in the body. The TERM_PROTO_ONLY means that we pick up only the protos from post.trm, even if current driver is being compiled with TERM_BODY or TERM_TABLE

If we do it the linked-list way, the arg to TERM_TABLE_START will be the name of the variable, so any valid, unique name is fine. The TERM_TABLE_START macro will do all the work of linking the entries together, probably using LAST_TERM

The inclusion of the TERM_HELP section (and removal of terminal documentation from the master gnuplot.doc file) means that the online help will include discussions of only those terminals available to the user. For generation of the printed manual, all can be included.

Please make as many things as possible static, but do still try to use unique names since all drivers may all be compiled into term.o

The bit in the PROTO section is basically what you would put into a .h file if we had them - everything that is needed by the TABLE_ENTRY should be defined in this part. In particular, dont forget all the maxes and character sizes and things for the table entry.

Dont forget to put TERM_PUBLIC in the defns of the fns as well as the prototypes. It will probably always expand to 'static' except for pcs.

Using Term::Gnuplot from C libraries

The interface of this module to gnuplot versions 3.7/3.8 is going via a translation layer in Gnuplot.h. This layer isolates low-level drawing routines from gnuplot program. (In doing this unsupported job it does some nasty thing, in particular, if you want Gnuplot.h to be included in more than one C compilation unit, define GNUPLOT_NO_CODE_EMIT before inclusion of Gnuplot.h in all but one compilation unit.)

In fact Gnuplot.h can be used by any C program or library which wants to use device-independent plotting routines of gnuplot.

C library should use the same syntax of calls as Term::Gnuplot, with the only difference that to call low-level _init() method one calls gptable_init(), to set terminal one calls termset(name), and to get a property of terminal (say xmax) one uses termprop(xmax).

To set options one can setup the array token and data c_token, num_tokens, input_line, then call options(). Alternately, one can define SET_OPTIONS_FROM_STRING, then a call set_options_from(string) is avalable. This call will set up all these variables and will call options(). However, the logic of the parsing of the string is very primitive.


  • To initialize the facilities of Gnuplot.h from C one needs to call setup_gpshim(). This call can be made as many times as wanted, only the first call will do anything.

  • NULL argument to term_set_output() means "reset back to stdout".

  • Gnuplot.h expects that the macro/function croak(...) is defined. This function should have the same syntax as printf(), and should not return. It is used as an error-reporting function.

  • One should define functions int StartOutput(), int EndOutput() and int OutLine(char *s) which will be used by gnuplot for error messages and for terminal listing. Alternatively, one can define GNUPLOT_OUTLINE_STDOUT, and gnuplot will put these messages to stdout.

There are two different ways to use the plotting calls via Gnuplot.h. One can either establish the link to gnuplot library at compile/link time, or to postpone this link to run time. By default Gnuplot.h provides the first way, to switch to the second way define DYNAMIC_GNUPLOT before including Gnuplot.h.

To establish a link at run time, one needs to load a dynamic library which is compiled from Gnuplot.h - but without DYNAMIC_GNUPLOT defined. Feed the result of the call to get_term_ftable() as an argument to set_term_ftable(), as in (with error-condition checking disabled):

  typedef struct t_ftable *(*g_ftable)(void);
  g_ftable g_ftable_addr;
  void *handle = dlopen("gnuterm.dll", mode);

  g_ftable_addr = (g_ftable) dlsym(handle, "get_term_ftable");

This means that any C library/program which uses the API provided by Gnuplot.h does not need to be even linked with gnuplot, neither it requires include files of gnuplot. If plotting is done in some situations only, one will not need the overhead of gnuplot plotting library (gnuterm.dll in the above example) unless plotting is requested.

To facilitate run time link the Term::Gnuplot Perl module provides a Perl subroutine get_term_ftable() which is a variant of C get_term_ftable() which returns an integer instead of an address. One can feed this integer to a C function v_set_term_ftable(void*), which will establish a runtime link. Thus the external XS library which wants to use Term::Gnuplot at runtime can put this in .xs file:

  #define int_set_term_ftable(a) (v_set_term_ftable((void*)a))
  extern  void v_set_term_ftable(void *a);

    IV a

include Gnuplot.h (with DYNAMIC_GNUPLOT defined) into any C file, and define this Perl subroutine

  sub link_gnuplot {
    eval 'use Term::Gnuplot 0.56; 1' or die;

in .pm file.

Now if it needs to do plotting, it calls link_gnuplot(), then does the plotting - without a need to interact with gnuplot at compile/link time, and having the additional burden of low-level plotting code loaded in the executable/DLL.

After a call link_gnuplot(), all the Gnuplot.h API calls made from the above C file will be directed through the vtables of the Perl module Term::Gnuplot.

Using different Plotting libraries

In fact Gnuplot.h knows almost nothing about gnuplot, with a notable exceptions that there is an API call term = change_term(name), which returns a table of methods. Thus in principle Gnuplot.h can establish a runtime-link with any plotting library which supports (or can be coerced to support) this call. (The table is assumed to be compatible with gnuplot layout of struct termentry.)

Gnuplot.h uses also a handful of other gnuplot APIs (such as changing output file and several initialization shortcuts), but they should be easy to be ignored if an interface to another plotting library is needed.

Convenience functions

get_terms(int n, const char **namep, const char **descrp)

Get n-th terminal's name and description into *namep, *descrp; returns FALSE if n is out of range. n is 0-based.

set_output_routines(OUTPUT_FUNC_t *f)
OUTPUT_FUNC_t *f = get_output_routines()

Set/get the routines used to output information. Useful to catch, e.g., the diagnostic output of the library, as in list_terms(). set_output_routines() returns TRUE on success, and ignores NULL entries in the structure OUTPUT_FUNC_t:

  typedef int (*START_END_OUTPUT_t)(void);
  typedef int (*DO_OUTPUT_LINE_t)(char *s);
  typedef struct {
    START_END_OUTPUT_t start_output_fun, end_output_fun;
    DO_OUTPUT_LINE_t output_line_fun;


High-level plotting

  sub ploth {
    my ($xmin, $xmax, $sub) = (shift, shift, shift);
    my $wpoints = scaled_xmax() - 1;
    my $hpoints = scaled_ymax() - 1;
    my $delta = ($xmax - $xmin)/$wpoints;
    my (@ys, $y);
    my ($ymin, $ymax) = (1e300, -1e300);
    my $x = $xmin;
    for my $i (0 .. $wpoints) {
      $y = $sub->($x);
      push @ys, $y;
      $ymin = $y if $ymin > $y;
      $ymax = $y if $ymax < $y;
      $x += $delta;
    my $deltay = ($ymax - $ymin)/$hpoints;
    $_ = ($_ - $ymin)/$deltay + $yfix for @ys;


    linewidth 1;
    linetype -2;
    move 0, $yfix;
    vector 0, $hpoints + $yfix;
    vector $wpoints, $hpoints + $yfix;
    vector $wpoints, $yfix;
    vector 0, $yfix;
    linetype -1;
    if ($xmin < 0 && $xmax > 0) {
      my $xzero = -$xmin/$delta;
      move $xzero, $yfix;
      vector $xzero, $hpoints + $yfix;
    if ($ymin < 0 && $ymax > 0) {
      my $yzero = -$ymin/$deltay + $yfix;
      move 0, $yzero;
      vector $wpoints, $yzero;

    linetype 0;
    move 0, int($ys[0] + 0.5);
    linetype 0;
    for my $i (1 .. $wpoints) {
      $x += $delta;
      vector $i, int($ys[$i] + 0.5);

This function should be used as in

  ploth(-1,3, sub { sin( (shift)**6 ) })

$yfix should be set to 1 for gif terminal to compensate for off-by-one bug.

Multifile plotting

  use strict;
  use Term::Gnuplot qw(:ALL);

  my ($yfix, $ext) = (1, 'gif');
  plot_outfile_set "manypl1.$ext";              # Need to set before plotterm()

  change_term "gif";
  set_options "size", 300, ',', 200;

  for my $k (1..6) {
    plot_outfile_set "manypl$k.$ext" unless $k == 1;
    ploth( -1, 3, sub { sin((shift)**$k) } );

Here we use the function ploth() from "High-level plotting", it should be in the same scope so that $yfix is visible there. Note that gif terminal requires $yfix to be 1 to circumvent a bug, and requires a literal ',' in the set_options call.

If a terminal does not support direct setting of the size of the output device, one may set global rescaling factors by calling plotsizes_scale():

  plotsizes_scale(300/xmax(), 200/ymax());


The following C macros are set to reasonable values, no peeking is performed to get correct values, this may break Gnuplot on some systems:


No testing for


macros is performed either, however, this may only increase size of the executable (since X11 module is not making any direct X calls, but calls an external program to serve the requests).

Apparently gif terminal has off-by-one error: yrange is 1..ymax(). All the bugs of gnuplot low-level plotting show in this module as well.

In many situations the line and point styles are automatically to a sane default at the start of the plot. However, one needs to set them up manually anyway; otherwise one can hit rare obscure problems when switching terminal types and output files.