Tcl/Tk Image formats (TkImg)
        (Version 1.4.16 / November 2023)

        Jan Nijtmans, Andreas Kupries, Paul Obermeier

This file contains a collection of format handlers for the Tk photo
image type, and a new image type, pixmaps. It can be used in
combination with Tcl/Tk 8.3 or later, but 8.6 or newer are highly
recommended.

Included in this distribution are the most recent versions (as of
July 2023) of the libz, libpng, libjpeg, and libtiff libraries.
These are not required, unless you need support for the PNG, JPEG,
or TIFF format. Note that you have to build these libraries to
support the named formats, even if your system already has shared
libraries for these formats. This is because the libraries here are
built such that they can be loaded as packages by the Tcl/Tk core,
making the handling of the various dependencies much easier. An
earlier version, 1.2.4, used a modified copy of Tcl's functions for
loading of shared libraries to load the support libraries at runtime.
These have been abandoned in favor of the new approach.

BACKGROUND TO BUILDING

The TkImg sources have been heavily refactored. Instead of building
one big package there are several small packages most of which are
independent of each other.

All packages employ a TEA based build system (configure/make) for
easy configuration and building. This means that 99% of the options
to configure are the same for all the packages.

All packages save for the supporting ones (see below) have names
starting with 'img'. For compatibility with older scripts the
package index file of the utility package 'img::base' declares
pseudo-package 'Img', which loads all packages provided by this
extension with the exception of formats dted, filr, ps and raw.
See below for details on these packages.

BUILDING - The convenient way

The toplevel directory of tkImg contains a configure file for
convenient configuration and building of all packages in the
extension.

Run this configure script in a build directory of your choice to
configure all packages, then run

    make all
    make install

in the build directory. The most important options for configure are
--prefix and --exec-prefix which tell the build system where to find
Tcl and Tk, and also where to install the results of the builds
(header, shared libraries, ...).

This convenient build installs all shared libraries in a single
directory 'Img<VERSION>, together with a union package index for all
packages.

If the builder requires only a subset of the packages he can use

    make all

to build all packages, but must not use 'make install' in the top
build directory. Instead run

    make install

in the sub directories of the build directory which contain the
requested packages, and their dependencies.

Note, that target install also builds the documentation based on
Tcl script dtplite. To build and install without documentation, use

    make install-libraries

PACKAGES AND THEIR DEPENDENCIES

This section is for people who want to bypass the master
configure/Makefile.

At the bottom of the hierarchy of dependencies are the 'support
packages'. They encapsulate the support libraries for ZIP, TIFF, PNG
and JPEG in packages directly loadable by Tcl. They provide the
functionality of their underlying libraries via stub-tables. The names
of these packages are:

    Name        Directory             Dependency
    -------------------------------------------------
    zlibtcl     tkimg/compat/libz
    pngtcl      tkimg/compat/libpng   zlibtcl
    jpegtcl     tkimg/compat/libjpeg
    tifftcl     tkimg/compat/libtiff
    -------------------------------------------------

The package 'pngtcl' depends on 'zlibtcl' and has to be built after
it. Beyond that the order of building is free. Their TEA build systems
can be found in the directories listed above.

The configure/Makefile's in the directories

    tkimg/compat/libz
    tkimg/compat/libpng
    tkimg/compat/libjpeg
    tkimg/compat/libtiff

must _not_ be used directly under any circumstances.


At the next level is the package 'tkimg'. It provides utility
functions used by all format handlers, and therefore has to be built
before any of them. Its TEA build system can be found in the directory

    Name        Directory       Dependency
    -------------------------------------------------
    img::base   tkimg/base
    -------------------------------------------------

Beyond that are the packages providing the various format
handlers. They can be built in any order. Some of them depend on
supporting packages, as noted below. Their names and directories are

    Name        Directory     Dependency
    -------------------------------------------------
    img::bmp    tkimg/bmp
    img::gif    tkimg/gif
    img::ico    tkimg/ico
    img::jpeg   tkimg/jpeg    jpegtcl
    img::pcx    tkimg/pcx
    img::pixmap tkimg/pixmap
    img::png    tkimg/png     pngtcl, zlibtcl
    img::ppm    tkimg/ppm
    img::sgi    tkimg/sgi
    img::sun    tkimg/sun
    img::tga    tkimg/tga
    img::tiff   tkimg/tiff    tifftcl, zlibtcl, jpegtcl
    img::window tkimg/window
    img::xbm    tkimg/xbm
    img::xpm    tkimg/xpm

    img::ps     tkimg/ps

    img::dted   tkimg/dted
    img::flir   tkimg/flir
    img::raw    tkimg/raw
    -------------------------------------------------

The packages img::dted, img::flir, img::raw and img::ps are special, because
they are not included when doing a "package require Img". They must be 
explicitely loaded via a "package require img::FMT".
img::ps reads Postscript or PDF files and transforms the first page into a
photo image using external program "gs".
As the current implementation might hang using larger PostScript files, 
it is not automatically loaded.
img::dted reads Digital Terrain Elevation Data and transforms the elevation
data into photo images.
img::flir reads FLIR files and transforms the temperature information
into photo images.
img::raw can transform any form of binary matrix data
(8-bit, 16-bit and 32-bit integer, 32-bit and 64-bit float) into a photo image.
As DTED and RAW files do not have a magic key or other identifier at the
beginning of the file, it is not possible to automatically detect the
format by reading some file header.

CONFIGURE

The source distributions have "configure", which  has the following
possibilities:
    configure ?options?

Some possible options:
    --prefix=<dir>      Install headers in <dir>/include.
                Default: "/usr/local"
    --exec-prefix=<dir> Install libraries in <dir>/lib.
                Default: "${prefix}"
    --with-tcl=<dir>    Find Tcl libraries in <dir> and include files in
                <dir>/../include or <dir>/../generic.
                Default: "${exec-prefix}/lib" or a sibling directory
                of the Img build directory.
    --with-tk=<dir>     Find Tk libraries in <dir> and include files in
                <dir>/../include or <dir>/../generic.
                Default: the same values as given by --with-tcl
                or a sibling directory of the Img build directory.

    Packages dependent on one or more of the support packages have
    appropriate options to locate their libraries and headers, if
    they cannot be found via --prefix and --exec-prefix

    Use configure --help to query each configure for the full set
    of options available to it.


MAKE & INSTALL

    'make' or 'make all' will build any package.

    'make install' will install its headers and libraries in the
    directories specified via --prefix/include and --exec-prefix/lib.

USE

If you want to use one or more of new image formats to be available in
your own scripts, add a line like the following somewhere in your
script:

    package require img::FORMAT

where FORMAT stands for the name of the format requested. See the list
in section 'PACKAGES AND THEIR DEPENDENCIES' for the available
formats. Each format will automatically load all of the packages it is
dependent on.

The line
    package require Img

is still legal and will load all format handlers provided by this
extension except dted, flir, ps and raw.

As an example, have a look at the file "demo.tcl"

For further options see the manpages.


DOCUMENTATION

The documentation coming with the distribution is written in the
doctools format (see tcllib).

PLATFORMS
    Tested:
        Linux           (gcc)
        Raspberry Pi OS (gcc)
        RiscV Debian    (gcc)
        Windows         (MSys/MinGW, Visual Studio C++)
        Darwin          (gcc)

    Other machines and OS's should work too.

Feedback about other OS's and compilers is appreciated. Please
help us in making this package better.

Jan Nijtmans    (nijtmans@users.sourceforge.net)
Andreas Kupries (andreas_kupries@users.sourceforge.net)
Paul Obermeier  (obermeier@users.sourceforge.net)