These are some notes on backward compatibility of the plotutils package, on
both the user and programmer levels.

Release 2.3
-----------

CGM output is now supported.  By default, a CGM Plotter emits
binary-encoded version-3 CGM format, conforming to the WebCGM profile.
(For information on WebCGM, see http://www.cgmopen.org .)  The CGM format
version number may be reduced by setting the libplot parameter (or
environment variable) CGM_MAX_VERSION.  Irrespective of version, a
human-readable CGM file, i.e., one encoded as clear text, may be produced
by setting CGM_ENCODING to "clear_text".  Clear text CGM files are valid
CGM files, though technically they don't conform to the WebCGM profile
(a WebCGM file is meant to be binary).

The package is now based on libplot version 3.0, which has new thread-safe
C and C++ APIs, i.e. APIs which (1) maintain no global state, and (2) are
pthread-aware.  The names of all new thread-safe libplot functions end in
"_r", for `reentrant' or `revised'.  Each of them takes a pointer to an
opaque plPlotter object as its first argument.

There are new functions in both libplot and libplotter for creating and
manipulating PlotterParams objects, which store Plotter parameters.
Parameters are copied from such an object when the Plotter class is
instantiated.

The old C and C++ API's are still supported, though deprecated.  So you can
still use pl_newpl() and pl_openpl(), etc., instead of pl_newpl_r() and
pl_openpl_r(), etc.

A new API function, pl_pentype_r(), has been added.  If its argument is 0,
stroking of paths, as opposed to filling, will be turned off.  So `edgeless
polygons' can now be drawn.

Fig and PCL Plotters now position their viewports (i.e. "graphics displays")
in the center of their pages, like PS Plotters.  So the PCL_XOFFSET and
PCL_YOFFSET parameters have been removed, and PCL_ROTATE too.  Similarly,
HPGL_XOFFSET and HPGL_YOFFSET parameters have been removed, even though tbe
viewport position for HP-GL Plotters has not changed.

Shifting of the viewport on the page, for PCL, HP-GL, Fig, and PS Plotters,
is now accomplished through the PAGESIZE parameter.  E.g., its value could
be "letter,xoffset=1in,yoffset=-2cm" or "a4,yoffset=12mm".

A new parameter, ROTATION, has been introduced; it applies to PCL, HP-GL,
Fig, and PS Plotters.  It defines rotation of the viewport on the page,
which is not the same as what the HPGL_ROTATE parameter, previously
introduced for HPGL Plotters, defines.  Values of ROTATION can be "no",
"yes", "0", "90", "180", "270".

A new scan-conversion library, called libxmi, is optionally built and
installed, together with documentation.  It contains the scan-conversion
code that is used by libplot's GIF and PNM drivers, which is based on the
X11 sample server code.  libxmi is also distributed independently.  The
libxmi version number is 1.1.

Release 2.2
-----------

Massive expansion of the C API, with new drivers, and introduction of
libplotter (C++ class library).  Backward compatibility of the C API
maintained, except that all functions now begin with "pl_".  Header file
"plotcompat.h", if needed, will redefine old function names as new function
names.  Libplot version number is now 2.0.

outfile() function, always more or less deprecated, now declared
obsolescent.  No longer documented.

Release 2.1.6
-------------

AI driver added, but libplot API unchanged.  Libplot version number is now
1.6.

Support in plot.h header file for old names for endpath() and filltype(),
which began in plotutils-2.0 (see below), finally dropped.

Release 2.1.5
-------------

PCL 5 driver added.  Kerning of device-resident `HP stick fonts' accessible
to the HP-GL driver, when HPGL_VERSION=1.5, also added.  Libplot API
unchanged, but libplot version number is now 1.5.


Release 2.1.2, 2.1.3, 2.1.4
---------------------------

No additions to libplot API, but the semantics of closepl() vs. deletepl()
have finally changed (programmers were warned about this in the texinfo
documentation).  The libplot version number is now 1.2 (upped to 1.3 for
release 2.1.3 and 1.4 for 2.1.4).

Plotter output, for non-realtime plotting, is now guaranteed to be emitted
only when deletepl() is called.  I.e., graphic output is not necessarily
written to the output stream after each page is closed.  In practice, this
affects only Postscript output.  Emitting PS only after the final page of a
multi-page graphics file is closed enables the PS to conform to the DSC
(Postscript Document Structuring Conventions).  

Support for many new stick fonts added (mostly available only if using 
`-T hpgl', with HPGL_VERSION=1.5.  `Stick fonts' are HP's device-resident 
vector fonts.

If using `-T hpgl' with HPGL_VERSION=1, circles and rectangles aligned 
with the coordinate axes can now be filled.

Names of many Hershey fonts changed, but old names continue to work.


Release 2.1.1
-------------

No additions to libplot API, though libplot was improved in various ways.
The libplot version number is now 1.1.

Release 2.1
-----------

No incompatibilities with plotutils release 2.0.  But many new command-line
options added to user-level utilities, and the libplot API was expanded by
the addition of bgcolor() and bgcolorname().  The libplot version number is
now 1.0.

Release 2.0
-----------

In release 2.0 the idea of separate variants of the `graph', `plot', and
`tek2plot' programs for each display device was finally done away with.
There is now only a single instance of each program.  The display device is
specified by the `-T' option.

The merging of the device-specific variants was made possible by the
merging of the device-specific variants of the libplot library on which
they were based.  There is now only a single library, which is structured
in an object-oriented way.  There are new functions, newpl(), selectpl(),
openpl(), which allow the creation of an arbitrarily large number of
`Plotter' objects simultaneously.  Each Plotter produces output for one
display device.

On startup of libplot, a single default Plotter is created and selected,
namely one that produces GNU metafile format.  This is for backward
compatibility: it allows programs written for earlier versions of GNU
libplot, and even Unix libplot, to link with it and run as expected.  If
you prefer a different default Plotter type, you should select it at
installation time.  For example, including -DDEFAULT_PLOTTER_TYPE=\"ps\"
in your CFLAGS option will cause the default Plotter to produce
Postscript output instead.

The libplot API changed in release 2.0 in a few other ways.

1. falabel() was dropped from the API, and alabel() no longer returns a
value related to the width of the text string that it renders.  If you need
to get the width of a text string, use flabelwidth() or labelwidth().

2. The semantics of the arc() primitive have changed.  It now draws an arc
that may be clockwise as well as counterclockwise, but is restricted to
have opening angle no more than 180 degrees.  Also, it moves the graphics
cursor position to the endpoint of the arc.

3. The box() primitive now moves the graphics cursor to the midpoint of the
box, rather than to the second-specified vertex.

4. endpoly() has been renamed endpath(), and fill() has been renamed
filltype().  These last changes are temporarily supported by the plot.h
include file.

As of release 2.0 of the package, libplot has its own, independent,
versioning system.  The version of libplot distributed with release 2.0 is
numbered 0.0.  Beginning with version 0.0, libplot is installed both as a
static library and as a shared library (a DLL), on machines that support
shared libraries.
