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Function: _header_graphic
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Section: graphic
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 \section{Plotting functions}

   Although plotting is not even a side purpose of PARI, a number of plotting
 functions are provided. There are three types of graphic functions.

 \subsec{High-level plotting functions} (all the functions starting with
 \kbd{ploth}) in which the user has little to do but explain what type of plot
 he wants, and whose syntax is similar to the one used in the preceding
 section.

 \subsec{Low-level plotting functions} (called \var{rectplot} functions,
 sharing the prefix \kbd{plot}), where every drawing primitive (point, line,
 box, etc.) is specified by the user. These low-level functions work as
 follows. You have at your disposal 16 virtual windows which are filled
 independently, and can then be physically ORed on a single window at
 user-defined positions. These windows are numbered from 0 to 15, and must be
 initialized before being used by the function \kbd{plotinit}, which specifies
 the height and width of the virtual window (called a \var{rectwindow} in the
 sequel). At all times, a virtual cursor (initialized at $[0,0]$) is attached
 to the window, and its current value can be obtained using the function
 \kbd{plotcursor}.

 A number of primitive graphic objects (called \var{rect} objects) can then
 be drawn in these windows, using a default color attached to that window
 (which can be changed using the \kbd{plotcolor} function) and only the part
 of the object which is inside the window will be drawn, with the exception of
 polygons and strings which are drawn entirely. The ones sharing the prefix
 \kbd{plotr} draw relatively to the current position of the virtual cursor,
 the others use absolute coordinates. Those having the prefix \kbd{plotrecth}
 put in the rectwindow a large batch of rect objects corresponding to the
 output of the related \kbd{ploth} function.

    Finally, the actual physical drawing is done using \kbd{plotdraw}. The
 rectwindows are preserved so that further drawings using the same windows at
 different positions or different windows can be done without extra work. To
 erase a window, use \kbd{plotkill}. It is not possible to partially erase a
 window: erase it completely, initialize it again, then fill it with the
 graphic objects that you want to keep.

    In addition to initializing the window, you may use a scaled window to
 avoid unnecessary conversions. For this, use \kbd{plotscale}. As long as this
 function is not called, the scaling is simply the number of pixels, the
 origin being at the upper left and the $y$-coordinates going downwards.

    Plotting functions are platform independent, but a number of graphical
 drivers are available for screen output: X11-windows (including
 Openwindows and Motif), Windows's Graphical Device Interface, the Qt and
 FLTK graphical libraries and one may even write the graphical objects to a
 PostScript or SVG file and use an external viewer to open it. The physical
 window opened by \kbd{plotdraw} or any of the \kbd{ploth*} functions is
 completely separated from \kbd{gp} (technically, a \kbd{fork} is done, and
 all memory unrelated to the graphics engine is immediately freed in the child
 process), which means you can go on working in the current \kbd{gp} session,
 without having to kill the window first. This window can be closed, enlarged
 or reduced using the standard window manager functions. No zooming procedure is
 implemented though.

 \subsec{Functions for PostScript or SVG output} in the same way that
 \kbd{printtex} allows you to have a \TeX\ output
 corresponding to printed results, the functions \kbd{plotexport},
 \kbd{plothexport} and \kbd{plothrawexport} convert a plot to a character
 string in either \tet{PostScript} or \tet{Scalable Vector Graphics} format.
 This string can then be written to a file in the customary way, using
 \kbd{write}. These export routines are available even if no Graphic Library is.
 \smallskip