FreeBASIC PNG Library (v1.9.0)

  Copyright (C) 2007 Simon Nash
  zlib code Copyright (C) 1995-2005 Jean-loup Gailly and Mark Adler
  See license.txt and zlib/zlib.h for more information.

  This library provides easy to use functions for using PNG images in your FreeBASIC
  programs.  The functions provide a way to load PNG images to old or new style PUT buffers
  and also in a format ready for use with OpenGL.  Images can be loaded from file, or 
  memory buffer.

  Compiling
  =========

  In order to compile you need GNU make, FreeBASIC 0.16 or newer, and GCC if you wish to
  compile in the zlib.  Just type 'make' in the main directory to make the default build.
  You can also do 'make STATICZ=1' to build the library to include zlib.  Other options
  are 'DEBUG=1', 'PROFILE=1' and 'EXX=1'.

  Notes for users of previous versions (before v1.8.4)
  ====================================================

  The librarys interface has changed, due to the new target parameter, and the old
  redundant target depth has been removed, the library always returns a 32 bit image.
  There is also now no error global variable, however if you compile with make DEBUG=1
  then much debugging info will be printed to the console

  Usage
  =====

  Once compiled you will need two files, 'build/libfbpng.a' and 'inc/fbpng.bi'.  These
  should be placed either in your projects directory, or in the lib/ and inc/ dirs of your
  FreeBASIC installation, along with the other libary and header files.

  There are 5 functions for users, I will give the details here:

  ------------------------------------------------------

  For those functions that accept a target, the following are the allowed values

  For an old style FreeBASIC buffer, as used in older versions of FB
	PNG_TARGET_FBOLD
  For a new style FreeBASIC buffer, as used in the newer versions of FB
	PNG_TARGET_FBNEW
  For a buffer that is ready to be used with OpenGL
	PNG_TARGET_OPENGL

  ------------------------------------------------------

	declare function png_load cdecl alias "png_load" _
		( _
			byref filename as string, _
			byval target   as png_target_e = PNG_TARGET_FBOLD _
		) as any ptr

  The filename parameter should be obvious, something like "foo.png"
  The target parameter is one of the values listed above, ie PNG_TARGET_FBOLD

  The return value will be a pointer to a buffer that contains the image in the format
  specified by target.  The returned buffer will always be a 32-bit image.

  If the function fails, then the return will be NULL

  It is the users responsibity to free the returned image when finished with, using
  the normal DEALLOCATE/free

  Example

    dim as any ptr img
	screenres 640, 480, 32
	img = png_load( "test.png" )
	if img <> NULL then
	  put( 0, 0 ), img
	  deallocate( img )
    else
      print "Failed to load"
    end if

  ------------------------------------------------------

	declare function png_load_mem cdecl alias "png_load_mem" _
		( _
			byval buffer     as any ptr, _
			byval buffer_len as integer, _
			byval target     as png_target_e = PNG_TARGET_FBOLD _
		) as any ptr

  The buffer parameter is a pointer to a memory location that holds a PNG image
  The buffer_len parameter is the size of this buffer, ie the files size
  The target parameter is one of the values listed above, ie PNG_TARGET_FBOLD

  The return value will be a pointer to a buffer that contains the image in the format
  specified by target.  The returned buffer will always be a 32-bit image.

  If the function fails, then the return will be NULL

  It is the users responsibity to free the returned image when finished with, using
  the normal DEALLOCATE/free

  ------------------------------------------------------

	declare function png_save cdecl alias "png_save" _
		( _
			byref filename as string, _
			byval img      as any ptr _
		) as integer

  The filename parameter should be obvious, something like "foo.png"
  The img parameter is a pointer to either a new or old style FreeBASIC buffer, the
  library will determine what type it is, it must be in 32-bit format.

  The return value will be 0 (zero) on success, and non zero otherwise

  ------------------------------------------------------

	declare sub png_dimensions cdecl alias "png_dimensions" _
		( _
			byref filename as string, _
			byref w        as uinteger, _
			byref h        as uinteger _
		)

  The filename parameter should be obvious, something like "foo.png"
  The w and h parameters (note the byref) are how the dimensions are returned

  If the sub fails, then then w and h will be zero

  Example

    dim as uinteger w, h
	png_dimensions( "test.png", w, h )
	print w, h

  ------------------------------------------------------

	declare sub png_dimensions_mem cdecl alias "png_dimensions_mem" _
		( _
			byval buffer as any ptr, _
			byref w      as uinteger, _
			byref h      as uinteger _
		)

  The buffer parameter is a pointer to a memory location that holds a PNG image
  The w and h parameters (note the byref) are how the dimensions are returned

  If the sub fails, then then w and h will be zero

  Credits
  =======

  Technical credits:
    victor for the FreeBASIC compiler, and the rest of the team for their work on it.
    The creators of the PNG format, and the RFC that was very useful for me.
    Willem van Schaik for the pngsuite of testing images.
    The creators of zlib, for the compression, and decompression routines.
    counting_pine, for one line of code that has since been eliminated, but was
      very helpful at the time.
    DrV for the memory leak detector
    Coderjeff and others for the Wiki manual
    The makers of all the other tools I use, especially GDB, valgrind, gcc, fasm, make
    cha0s for building the windows prebuilt version
  General greetings:
    All FreeBASIC users, especially those who are on the IRC channel and the forum, in
    particular (but in no particular order)
      mr_cha0s, stylin, {1000101}, voodooattack, {Nathan}, spaz, pritchard, 
      shadowwolf, insomninja, ijjekw, DJ Peters, relsoft, Dr_D

  Notes on the zlib usage
  =======================

  The source files for zlib are just taken directly from an official zlib distribution
  I haven't modified them in any way