source-engine/thirdparty/libpng/contrib/gregbook/README

                     ===========================
                      PNG: The Definitive Guide
                     ===========================

                             Source Code

Chapters 13, 14 and 15 of "PNG: The Definitive Guide" discuss three free,
cross-platform demo programs that show how to use the libpng reference
library:  rpng, rpng2 and wpng.  rpng and rpng2 are viewers; the first is
a very simple example that that shows how a standard file-viewer might use
libpng, while the second is designed to process streaming data and shows
how a web browser might be written.  wpng is a simple command-line program
that reads binary PGM and PPM files (the ``raw'' grayscale and RGB subsets
of PBMPLUS/NetPBM) and converts them to PNG.

The source code for all three demo programs currently compiles under
Unix, OpenVMS, and 32-bit Windows.  (Special thanks to Martin Zinser,
zinser at decus.de, for making the necessary changes for OpenVMS and for
providing an appropriate build script.)  Build instructions can be found
below.

Files:

   README             this file
   LICENSE            terms of distribution and reuse (BSD-like or GNU GPL)
   COPYING            GNU General Public License (GPL)

   Makefile.unx       Unix makefile
   Makefile.w32       Windows (MSVC) makefile
   makevms.com        OpenVMS build script

   rpng-win.c         Windows front end for the basic viewer
   rpng-x.c           X Window System (Unix, OpenVMS) front end
   readpng.c          generic back end for the basic viewer
   readpng.h          header file for the basic viewer

   rpng2-win.c        Windows front end for the progressive viewer
   rpng2-x.c          X front end for the progressive viewer
   readpng2.c         generic back end for the progressive viewer
   readpng2.h         header file for the progressive viewer

   wpng.c             generic (text) front end for the converter
   writepng.c         generic back end for the converter
   writepng.h         header file for the converter

   toucan.png         transparent PNG for testing (by Stefan Schneider)

Note that, although the programs are designed to be functional, their
primary purpose is to illustrate how to use libpng to add PNG support to
other programs.  As such, their user interfaces are crude and definitely
are not intended for everyday use.

Please see http://www.libpng.org/pub/png/pngbook.html for further infor-
mation and links to the latest version of the source code, and Chapters
13-15 of the book for detailed discussion of the three programs.

Greg Roelofs
https://pobox.com/~newt/greg_contact.html
16 March 2008


BUILD INSTRUCTIONS

 - Prerequisites (in order of compilation):

      - zlib            https://zlib.net/
      - libpng          http://www.libpng.org/pub/png/libpng.html
      - pngbook         http://www.libpng.org/pub/png/book/sources.html

     The pngbook demo programs are explicitly designed to demonstrate proper
     coding techniques for using the libpng reference library.  As a result,
     you need to download and build both zlib (on which libpng depends) and
     libpng.  A common build setup is to place the zlib, libpng and pngbook
     subdirectory trees ("folders") in the same parent directory.  Then the
     libpng build can refer to files in ../zlib (or ..\zlib or [-.zlib]),
     and similarly for the pngbook build.

     Note that all three packages are designed to be built from a command
     line by default; those who wish to use a graphical or other integrated
     development environments are on their own.


 - Unix:

     Unpack the latest pngbook sources (which should correspond to this
     README file) into a directory and change into that directory.

     Copy Makefile.unx to Makefile and edit the PNG* and Z* variables
     appropriately (possibly also the X* variables if necessary).

     make

     There is no "install" target, so copy the three executables somewhere
     in your path or run them from the current directory.  All three will
     print a basic usage screen when run without any command-line arguments;
     see the book for more details.


 - Windows:

     Unpack the latest pngbook sources (which should correspond to this
     README file) into a folder, open a "DOS shell" or "command prompt"
     or equivalent command-line window, and cd into the folder where you
     unpacked the source code.

     For MSVC, set up the necessary environment variables by invoking

        %devstudio%\vc\bin\vcvars32.bat

     where where %devstudio% is the installation directory for MSVC /
     DevStudio.  If you get "environment out of space" errors under 95/98,
     create a desktop shortcut with "c:\windows\command.com /e:4096" as
     the program command line and set the working directory to the pngbook
     directory.  Then double-click to open the new DOS-prompt window with
     a bigger environment and retry the commands above.

     Copy Makefile.w32 to Makefile and edit the PNGPATH and ZPATH variables
     appropriately (possibly also the "INC" and "LIB" variables if needed).
     Note that the names of the dynamic and static libpng and zlib libraries
     used in the makefile may change in later releases of the libraries.
     Also note that, as of libpng version 1.0.5, MSVC DLL builds do not work.
     This makefile therefore builds statically linked executables, but if
     the DLL problems ever get fixed, uncommenting the appropriate PNGLIB
     and ZLIB lines will build dynamically linked executables instead.

     Do the build by typing

        nmake

     The result should be three executables:  rpng-win.exe, rpng2-win.exe,
     and wpng.exe.  Copy them somewhere in your PATH or run them from the
     current folder.  Like the Unix versions, the two windowed programs
     (rpng and rpng2) now display a usage screen in a console window when
     invoked without command-line arguments; this is new behavior as of
     the June 2001 release.  Note that the programs use the Unix-style "-"
     character to specify options, instead of the more common DOS/Windows
     "/" character.  (For example:  "rpng2-win -bgpat 4 foo.png", not
     "rpng2-win /bgpat 4 foo.png")


 - OpenVMS:

     Unpack the pngbook sources into a subdirectory and change into that
     subdirectory.

     Edit makevms.com appropriately, specifically the zpath and pngpath
     variables.

     @makevms

     To run the programs, they probably first need to be set up as "foreign
     symbols," with "disk" and "dir" set appropriately:

     $ rpng  == "$disk:[dir]rpng-x.exe"
     $ rpng2 == "$disk:[dir]rpng2-x.exe"
     $ wpng  == "$disk:[dir]wpng.exe"

     All three will print a basic usage screen when run without any command-
     line arguments; see the book for more details.  Note that the options
     style is Unix-like, i.e., preceded by "-" rather than "/".


RUNNING THE PROGRAMS:  (VERY) BRIEF INTRO

     rpng is a simple PNG viewer that can display transparent PNGs with a
     specified background color; for example,

        rpng -bgcolor \#ff0000 toucan.png

     would display the image with a red background.  rpng2 is a progressive
     viewer that simulates a web browser in some respects; it can display
     images against either a background color or a dynamically generated
     background image.  For example:

        rpng2 -bgpat 16 toucan.png

     wpng is a purely command-line image converter from binary PBMPLUS/NetPBM
     format (.pgm or .ppm) to PNG; for example,

        wpng -time < toucan-notrans.ppm > toucan-notrans.png

     would convert the specified PPM file (using redirection) to PNG, auto-
     matically setting the PNG modification-time chunk.

     All options can be abbreviated to the shortest unique value; for example,
     "-bgc" for -bgcolor (versus "-bgp" for -bgpat), or "-g" for -gamma.