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PNG: The Definitive Guide

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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@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

http://pobox.com/~newt/greg_contact.html

16 March 2008

BUILD INSTRUCTIONS

- Prerequisites (in order of compilation):

- zlib http://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.