Source

gd-libgd / src / readme.txt

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                                   gd 1.7.2
                                       
A graphics library for fast image creation

Follow this link to the latest version of this document.

     _HEY! READ THIS!_ gd 1.7.2 creates PNG images, not GIF images. This
     is a good thing. PNG is a more compact format, and full compression
     is available. Existing code will need modification to call
     gdImagePng instead of gdImageGif. _Please do not ask us to send you
     the old GIF version of GD._ Unisys holds a patent on the LZW
     compression algorithm, which is used in fully compressed GIF
     images. We are still investigating the legal issues surrounding
     various alternative means of producing a valid GIF file.
     
     gd 1.7.2 _requires_ that the following libraries also be installed:
     
     libpng
     
     zlib
     
     If you want to use the TrueType font support, you must also install
     the _Freetype library_, including the _freetype.h header file_. See
     the Freetype Home Page. No, I cannot explain why that site is down
     on a particular day, and no, I can't send you a copy.
     
     If you want to use the Xpm color bitmap loading support, you must
     also have the X Window System and the Xpm library installed (Xpm is
     often included in modern X distributions).
     
     Please read the documentation and install the required libraries.
     Do not send email asking why png.h is not found. See the
     requirements section for more information. Thank you!
     
  Table of Contents
  
     * Credits and license terms
     * What's new in version 1.7.2?
     * What's new in version 1.7.1?
     * What's new in version 1.7?
     * What's new in version 1.6.3?
     * What's new in version 1.6.2?
     * What's new in version 1.6.1?
     * What's new in version 1.6?
     * What is gd?
     * What if I want to use another programming language?
     * What else do I need to use gd?
     * How do I get gd?
     * How do I build gd?
     * gd basics: using gd in your program
     * webpng: a useful example
     * Function and type reference by category
     * About the additional .gd image file format
     * Please tell us you're using gd!
     * If you have problems
     * Alphabetical quick index
       
   Up to the Boutell.Com, Inc. Home Page
   
  Credits and license terms
  
   In order to resolve any possible confusion regarding the authorship of
   gd, the following copyright statement covers all of the authors who
   have required such a statement. _If you are aware of any oversights in
   this copyright notice, please contact Thomas Boutell who will be
   pleased to correct them._

COPYRIGHT STATEMENT FOLLOWS THIS LINE

     Portions copyright 1994, 1995, 1996, 1997, 1998, 1999, by Cold
     Spring Harbor Laboratory. Funded under Grant P41-RR02188 by the
     National Institutes of Health.
     
     Portions copyright 1996, 1997, 1998, 1999, by Boutell.Com, Inc.
     
     Portions relating to GD2 format copyright 1999 Philip Warner.
     
     Portions relating to PNG copyright 1999, Greg Roelofs.
     
     Portions relating to libttf copyright 1999, John Ellson
     (ellson@lucent.com).
     
     _Permission has been granted to copy and distribute gd in any
     context without fee, including a commercial application, provided
     that this notice is present in user-accessible supporting
     documentation._
     
     This does not affect your ownership of the derived work itself, and
     the intent is to assure proper credit for the authors of gd, not to
     interfere with your productive use of gd. If you have questions,
     ask. "Derived works" includes all programs that utilize the
     library. Credit must be given in user-accessible documentation.
     
     _This software is provided "AS IS."_ The copyright holders disclaim
     all warranties, either express or implied, including but not
     limited to implied warranties of merchantability and fitness for a
     particular purpose, with respect to this code and accompanying
     documentation.
     
     Although their code does not appear in gd 1.7.2, the authors wish
     to thank David Koblas, David Rowley, and Hutchison Avenue Software
     Corporation for their prior contributions.
     
END OF COPYRIGHT STATEMENT

  What is gd?
  
   gd is a graphics library. It allows your code to quickly draw images
   complete with lines, arcs, text, multiple colors, cut and paste from
   other images, and flood fills, and write out the result as a .PNG
   file. This is particularly useful in World Wide Web applications,
   where .PNG is one of the formats accepted for inline images by most
   browsers.
   
   gd is not a paint program. If you are looking for a paint program, you
   are looking in the wrong place. If you are not a programmer, you are
   looking in the wrong place.
   
   gd does not provide for every possible desirable graphics operation.
   It is not necessary or desirable for gd to become a kitchen-sink
   graphics package, but version 1.7.2 incorporates most of the commonly
   requested features for an 8-bit 2D package. Support for truecolor
   images, JPEG and truecolor PNG is planned for version 2.0.
   
  What if I want to use another programming language?
  
    Perl
    
   gd can also be used from Perl, courtesy of Lincoln Stein's GD.pm
   library, which uses gd as the basis for a set of Perl 5.x classes.
   Updated to gd 1.6 and up.
   
    Tcl
    
   gd can be used from Tcl with John Ellson's Gdtclft dynamically loaded
   extension package. (Gdtclft2.0 or later is needed for gd-1.6 and up
   with PNG output.)
   
    Any Language
    
   There are, at the moment, at least three simple interpreters that
   perform gd operations. You can output the desired commands to a simple
   text file from whatever scripting language you prefer to use, then
   invoke the interpreter.
   
   These packages have not been updated to gd 1.6 and up as of this
   writing.
     * tgd, by Bradley K. Sherman
     * fly, by Martin Gleeson
       
  What's new in version 1.7.2?
  
   An uninitialized-pointer bug in gdtestttf.c was corrected. This bug
   caused crashes at the end of each call to gdImageStringTTF on some
   platforms. Thanks to Wolfgang Haefelinger.
   
   Documentation fixes. Thanks to Dohn Arms.
   
   Makefile fixes to permit linking with all libraries required on
   platforms with order- dependent linkers.
   
  What's new in version 1.7.1?
  
   A minor buglet in the Makefile was corrected, as well as an inaccurate
   error message in gdtestttf.c. Thanks to Masahito Yamaga.
   
  What's new in version 1.7?
  
   Version 1.7 contains the following changes:
     * Japanese language support for the TrueType functions. Thanks to
       Masahito Yamaga.
     * autoconf and configure have been removed, in favor of a carefully
       designed Makefile which produces and properly installs the library
       and the binaries. System-dependent variables are at the top of the
       Makefile for easy modification. I'm sorry, folks, but autoconf
       generated _many, many confused email messages_ from people who
       didn't have things where autoconf expected to find them. I am not
       an autoconf/automake wizard, and gd is a simple, very compact
       library which does not need to be a shared library. I _did_ make
       many improvements over the old gd 1.3 Makefile, which were
       directly inspired by the autoconf version found in the 1.6 series
       (thanks to John Ellson).
     * Completely ANSI C compliant, according to the -pedantic-errors
       flag of gcc. Several pieces of not-quite-ANSI-C code were causing
       problems for those with non-gcc compilers.
     * gdttf.c patched to allow the use of Windows symbol fonts, when
       present (thanks to Joseph Peppin).
     * extern "C" wrappers added to gd.h and the font header files for
       the convenience of C++ programmers. bdftogd was also modified to
       automatically insert these wrappers into future font header files.
       Thanks to John Lindal.
     * Compiles correctly on platforms that don't define SEEK_SET. Thanks
       to Robert Bonomi.
     * Loads Xpm images via the gdImageCreateFromXpm function, if the Xpm
       library is available. Thanks to Caolan McNamara.
       
  What's new in version 1.6.3?
  
   Version 1.6.3 corrects a memory leak in gd_png.c. This leak caused a
   significant amount of memory to be allocated and not freed when
   writing a PNG image.
   
  What's new in version 1.6.2?
  
   Version 1.6.2 from John Ellson adds two new functions:
     * gdImageStringTTF - scalable, rotatable, anti-aliased, TrueType
       strings using the FreeType library, but only if libttf is found by
       configure. _We do not provide TrueType fonts. Obtaining them is
       entirely up to you._
     * gdImageColorResolve - an efficient alternative for the common code
       fragment:


      if ((color=gdImageColorExact(im,R,G,B)) < 0)
          if ((color=gdImageColorAllocate(im,R,G,B)) < 0)
              color=gdImageColorClosest(im,R,G,B);

   Also in this release the build process has been converted to GNU
   autoconf/automake/libtool conventions so that both (or either) static
   and shared libraries can be built.
   
  What's new in version 1.6.1?
  
   Version 1.6.1 incorporates superior PNG reading and writing code from
   Greg Roelofs, with minor modifications by Tom Boutell. Specifically, I
   altered his code to read non-palette images (converting them to
   palette images badly, by dithering them), and to tolerate palette
   images with types of transparency that gd doesn't actually support (it
   just ignores the advanced transparency features). Any bugs in this
   area are therefore my fault, not Greg's.
   
   Unlike gd 1.6, users should have no trouble linking with gd 1.6.1 if
   they follow the instructions and install all of the pieces. However,
   _If you get undefined symbol errors, be sure to check for older
   versions of libpng in your library directories!_
   
  What's new in version 1.6?
  
   Version 1.6 features the following changes:
   
   _Support for 8-bit palette PNG images has been added. Support for GIF
   has been removed._ This step was taken to completely avoid the legal
   controversy regarding the LZW compression algorithm used in GIF.
   Unisys holds a patent which is relevant to LZW compression. PNG is a
   superior image format in any case. Now that PNG is supported by both
   Microsoft Internet Explorer and Netscape (in their recent releases),
   we highly recommend that GD users upgrade in order to get
   well-compressed images in a format which is legally unemcumbered.
   
  What's new in version 1.5?
  
   Version 1.5 featured the following changes:
   
   _New GD2 format_
          An improvement over the GD format, the GD2 format uses the zlib
          compression library to compress the image in chunks. This
          results in file sizes comparable to GIFs, with the ability to
          access parts of large images without having to read the entire
          image into memory.
          
          This format also supports version numbers and rudimentary
          validity checks, so it should be more 'supportable' than the
          previous GD format.
          
   _Re-arranged source files_
          gd.c has been broken into constituant parts: io, gif, gd, gd2
          and graphics functions are now in separate files.
          
   _Extended I/O capabilities._
          The source/sink feature has been extended to support GD2 file
          formats (which require seek/tell functions), and to allow more
          general non-file I/O.
          
   _Better support for Lincoln Stein's Perl Module_
          The new gdImage*Ptr function returns the chosen format stored
          in a block of memory. This can be directly used by the GD perl
          module.
          
   _Added functions_
          gdImageCreateFromGd2Part - allows retrieval of part of an image
          (good for huge images, like maps),
          gdImagePaletteCopy - Copies a palette from one image to
          another, doing it's best to match the colors in the target
          image to the colors in the source palette.
          gdImageGd2, gdImageCreateFromGd2 - Support for new format
          gdImageCopyMerge - Merges two images (useful to highlight part
          of an image)
          gdImageCopyMergeGray - Similar to gdImageCopyMerge, but tries
          to preserve source image hue.
          gdImagePngPtr, gdImageGdPtr, gdImageGd2Ptr - return memort
          blocks for each type of image.
          gdImageCreateFromPngCtx, gdImageCreateFromGdCtx,
          gdImageCreateFromGd2Ctx, gdImageCreateFromGd2PartCtx - Support
          for new I/O context.
          
   _NOTE:_ In fairness to Thomas Boutell, any bug/problems with any of
   the above features should probably be reported to Philip Warner.
   
  What's new in version 1.4?
  
   Version 1.4 features the following changes:
   
   Fixed polygon fill routine (again)
          Thanks to Kirsten Schulz, version 1.4 is able to fill numerous
          types of polygons that caused problems with previous releases,
          including version 1.3.
          
   Support for alternate data sources
          Programmers who wish to load a GIF from something other than a
          stdio FILE * stream can use the new gdImageCreateFromPngSource
          function.
          
   Support for alternate data destinations
          Programmers who wish to write a GIF to something other than a
          stdio FILE * stream can use the new gdImagePngToSink function.
          
   More tolerant when reading GIFs
          Version 1.4 does not crash when reading certain animated GIFs,
          although it still only reads the first frame. Version 1.4 also
          has overflow testing code to prevent crashes when reading
          damaged GIFs.
          
  What's new in version 1.3?
  
   Version 1.3 features the following changes:
   
   Non-LZW-based GIF compression code
          Version 1.3 contained GIF compression code that uses simple Run
          Length Encoding instead of LZW compression, while still
          retaining compatibility with normal LZW-based GIF decoders
          (your browser will still like your GIFs). _LZW compression is
          patented by Unisys. We are currently reevaluating the approach
          taken by gd 1.3. The current release of gd does not support
          this approach. We recommend that you use the current release,
          and generate PNG images._ Thanks to Hutchison Avenue Software
          Corporation for contributing the RLE GIF code.
          
   8-bit fonts, and 8-bit font support
          This improves support for European languages. Thanks are due to
          Honza Pazdziora and also to Jan Pazdziora . Also see the
          provided bdftogd Perl script if you wish to convert fixed-width
          X11 fonts to gd fonts.
          
   16-bit font support (no fonts provided)
          Although no such fonts are provided in the distribution, fonts
          containing more than 256 characters should work if the
          gdImageString16 and gdImageStringUp16 routines are used.
          
   Improvements to the "webpng" example/utility
          The "webpng" utility is now a slightly more useful application.
          Thanks to Brian Dowling for this code.
          
   Corrections to the color resolution field of GIF output
          Thanks to Bruno Aureli.
          
   Fixed polygon fills
          A one-line patch for the infamous polygon fill bug, courtesy of
          Jim Mason. I believe this fix is sufficient. However, if you
          find a situation where polygon fills still fail to behave
          properly, please send code that demonstrates the problem, _and_
          a fix if you have one. Verifying the fix is important.
          
   Row-major, not column-major
          Internally, gd now represents the array of pixels as an array
          of rows of pixels, rather than an array of columns of pixels.
          This improves the performance of compression and decompression
          routines slightly, because horizontally adjacent pixels are now
          next to each other in memory. _This should not affect properly
          written gd applications, but applications that directly
          manipulate the pixels array will require changes._
          
  What else do I need to use gd?
  
   To use gd, you will need an ANSI C compiler. _All popular Windows 95
   and NT C compilers are ANSI C compliant._ Any full-ANSI-standard C
   compiler should be adequate. _The cc compiler released with SunOS
   4.1.3 is not an ANSI C compiler. Most Unix users who do not already
   have gcc should get it. gcc is free, ANSI compliant and a de facto
   industry standard. Ask your ISP why it is missing._
   
   As of version 1.6, you also need the zlib compression library, and the
   libpng library. As of version 1.6.2, you can draw text using
   antialiased TrueType fonts if you also have the libttf library
   installed, but this is not mandatory. zlib is available for a variety
   of platforms from the zlib web site. libpng is available for a variety
   of platforms from the PNG web site.
   
   You will also want a PNG viewer, if you do not already have one for
   your system, since you will need a good way to check the results of
   your work. Netscape 4.04 and higher, and Microsoft Internet Explorer
   4.0 or higher, both support PNG. For some purposes you might be
   happier with a package like Lview Pro for Windows or xv for X. There
   are PNG viewers available for every graphics-capable modern operating
   system, so consult newsgroups relevant to your particular system.
   
  How do I get gd?
  
    By HTTP
    
     * Gzipped Tar File (Unix)
     * .ZIP File (Windows)
       
    By FTP
    
     * Gzipped Tar File (Unix)
     * .ZIP File (Windows)
       
  How do I build gd?
  
   In order to build gd, you must first unpack the archive you have
   downloaded. If you are not familiar with tar and gunzip (Unix) or ZIP
   (Windows), please consult with an experienced user of your system.
   Sorry, we cannot answer questions about basic Internet skills.
   
   Unpacking the archive will produce a directory called "gd-1.7.2".
   
    For Unix
    
   cd to the 1.7.2 directory. Edit the Makefile with your preferred text
   editor and make any necessary changes to the settings at the top,
   especially if you want Xpm or TrueType support. Next, type "make". If
   you are the system administrator, and you wish to make the gd library
   available to other programs, you may also wish to type "make install".
   
   If you get errors, edit the Makefile again, paying special attention
   to the INCLUDEDIRS and LIBDIRS settings.
   
    For Windows, Mac, Et Cetera
    
   Create a project using your favorite programming environment. Copy all
   of the gd files to the project directory. Add gd.c to your project.
   Add other source files as appropriate. Learning the basic skills of
   creating projects with your chosen C environment is up to you.
   
   You have now built both the gd library and a demonstration program
   which shows off the capabilities of gd. To see it in action, type
   "gddemo".
   
   gddemo should execute without incident, creating the file demoout.png.
   (Note there is also a file named demoin.png, which is provided in the
   package as part of the demonstration.)
   
   Display demoout.png in your PNG viewer. The image should be 128x128
   pixels and should contain an image of the space shuttle with quite a
   lot of graphical elements drawn on top of it.
   
   (If you are missing the demoin.png file, the other items should appear
   anyway.)
   
   Look at demoin.png to see the original space shuttle image which was
   scaled and copied into the output image.
   
  gd basics: using gd in your program
  
   gd lets you create PNG images on the fly. To use gd in your program,
   include the file gd.h, and link with the libgd.a library produced by
   "make libgd.a", under Unix. Under other operating systems you will add
   gd.c to your own project.
   
   If you want to use the provided fonts, include gdfontt.h, gdfonts.h,
   gdfontmb.h, gdfontl.h and/or gdfontg.h. For more impressive results,
   install libttf and use the new gdImageStringTTF function. If you are
   not using the provided Makefile and/or a library-based approach, be
   sure to include the source modules as well in your project. (They may
   be too large for 16-bit memory models, that is, 16-bit DOS and
   Windows.)
   
   Here is a short example program. _(For a more advanced example, see
   gddemo.c, included in the distribution. gddemo.c is NOT the same
   program; it demonstrates additional features!)_
   
/* Bring in gd library functions */
#include "gd.h"

/* Bring in standard I/O so we can output the PNG to a file */
#include <stdio.h>

int main() {
        /* Declare the image */
        gdImagePtr im;
        /* Declare an output file */
        FILE *out;
        /* Declare color indexes */
        int black;
        int white;

        /* Allocate the image: 64 pixels across by 64 pixels tall */
        im = gdImageCreate(64, 64);

        /* Allocate the color black (red, green and blue all minimum).
                Since this is the first color in a new image, it will
                be the background color. */
        black = gdImageColorAllocate(im, 0, 0, 0);

        /* Allocate the color white (red, green and blue all maximum). */
        white = gdImageColorAllocate(im, 255, 255, 255);
        
        /* Draw a line from the upper left to the lower right,
                using white color index. */
        gdImageLine(im, 0, 0, 63, 63, white);

        /* Open a file for writing. "wb" means "write binary", important
                under MSDOS, harmless under Unix. */
        out = fopen("test.png", "wb");

        /* Output the image to the disk file. */
        gdImagePng(im, out);

        /* Close the file. */
        fclose(out);

        /* Destroy the image in memory. */
        gdImageDestroy(im);
}

   When executed, this program creates an image, allocates two colors
   (the first color allocated becomes the background color), draws a
   diagonal line (note that 0, 0 is the upper left corner), writes the
   image to a PNG file, and destroys the image.
   
   The above example program should give you an idea of how the package
   works. gd provides many additional functions, which are listed in the
   following reference chapters, complete with code snippets
   demonstrating each. There is also an alphabetical index.
   
  Webpng: a more powerful gd example
  
   Webpng is a simple utility program to manipulate PNGs from the command
   line. It is written for Unix and similar command-line systems, but
   should be easily adapted for other environments. Webpng allows you to
   set transparency and interlacing and output interesting information
   about the PNG in question.
   
   webpng.c is provided in the distribution. Unix users can simply type
   "make webpng" to compile the program. Type "webpng" with no arguments
   to see the available options.
   
Function and type reference

     * Types
     * Image creation, destruction, loading and saving
     * Drawing, styling, brushing, tiling and filling functions
     * Query functions (not color-related)
     * Font and text-handling functions
     * Color handling functions
     * Copying and resizing functions
     * Miscellaneous Functions
     * Constants
       
  Types
  
   gdImage_(TYPE)_
          The data structure in which gd stores images. gdImageCreate
          returns a pointer to this type, and the other functions expect
          to receive a pointer to this type as their first argument. You
          may read the members sx (size on X axis), sy (size on Y axis),
          colorsTotal (total colors), red (red component of colors; an
          array of 256 integers between 0 and 255), green (green
          component of colors, as above), blue (blue component of colors,
          as above), and transparent (index of transparent color, -1 if
          none); please do so using the macros provided. Do NOT set the
          members directly from your code; use the functions provided.
          

typedef struct {
        unsigned char ** pixels;
        int sx;
        int sy;
        int colorsTotal;
        int red[gdMaxColors];
        int green[gdMaxColors];
        int blue[gdMaxColors];
        int open[gdMaxColors];
        int transparent;
} gdImage;

   gdImagePtr _(TYPE)_
          A pointer to an image structure. gdImageCreate returns this
          type, and the other functions expect it as the first argument.
          
   gdFont _(TYPE)_
          A font structure. Used to declare the characteristics of a
          font. Plese see the files gdfontl.c and gdfontl.h for an
          example of the proper declaration of this structure. You can
          provide your own font data by providing such a structure and
          the associated pixel array. You can determine the width and
          height of a single character in a font by examining the w and h
          members of the structure. If you will not be creating your own
          fonts, you will not need to concern yourself with the rest of
          the components of this structure.
          

typedef struct {
        /* # of characters in font */
        int nchars;
        /* First character is numbered... (usually 32 = space) */
        int offset;
        /* Character width and height */
        int w;
        int h;
        /* Font data; array of characters, one row after another.
                Easily included in code, also easily loaded from
                data files. */
        char *data;
} gdFont;

   gdFontPtr _(TYPE)_
          A pointer to a font structure. Text-output functions expect
          these as their second argument, following the gdImagePtr
          argument. Two such pointers are declared in the provided
          include files gdfonts.h and gdfontl.h.
          
   gdPoint _(TYPE)_
          Represents a point in the coordinate space of the image; used
          by gdImagePolygon and gdImageFilledPolygon.
          

typedef struct {
        int x, y;
} gdPoint, *gdPointPtr;

   gdPointPtr _(TYPE)_
          A pointer to a gdPoint structure; passed as an argument to
          gdImagePolygon and gdImageFilledPolygon.
          
   gdSource _(TYPE)_

typedef struct {
        int (*source) (void *context, char *buffer, int len);
        void *context;
} gdSource, *gdSourcePtr;

   Represents a source from which a PNG can be read. Programmers who do
   not wish to read PNGs from a file can provide their own alternate
   input mechanism, using the gdImageCreateFromPngSource function. See
   the documentation of that function for an example of the proper use of
   this type.
   
   gdSink _(TYPE)_

typedef struct {
        int (*sink) (void *context, char *buffer, int len);
        void *context;
} gdSink, *gdSinkPtr;

   Represents a "sink" (destination) to which a PNG can be written.
   Programmers who do not wish to write PNGs to a file can provide their
   own alternate output mechanism, using the gdImagePngToSink function.
   See the documentation of that function for an example of the proper
   use of this type.
   
  Image creation, destruction, loading and saving
  
   gdImageCreate(sx, sy) _(FUNCTION)_
          gdImageCreate is called to create images. Invoke gdImageCreate
          with the x and y dimensions of the desired image. gdImageCreate
          returns a gdImagePtr to the new image, or NULL if unable to
          allocate the image. The image must eventually be destroyed
          using gdImageDestroy().
          

... inside a function ...
gdImagePtr im;
im = gdImageCreate(64, 64);
/* ... Use the image ... */
gdImageDestroy(im);

   gdImageCreateFromPng(FILE *in) _(FUNCTION)_
          gdImageCreateFromPngCtx(gdIOCtx *in) _(FUNCTION)_
          
          
          gdImageCreateFromPng is called to load images from PNG format
          files. Invoke gdImageCreateFromPng with an already opened
          pointer to a file containing the desired image.
          gdImageCreateFromPng returns a gdImagePtr to the new image, or
          NULL if unable to load the image (most often because the file
          is corrupt or does not contain a PNG image).
          gdImageCreateFromPng does _not_ close the file. You can inspect
          the sx and sy members of the image to determine its size. The
          image must eventually be destroyed using gdImageDestroy().
          

gdImagePtr im;
... inside a function ...
FILE *in;
in = fopen("mypng.png", "rb");
im = gdImageCreateFromPng(in);
fclose(in);
/* ... Use the image ... */
gdImageDestroy(im);

   gdImageCreateFromPngSource(gdSourcePtr in) _(FUNCTION)_
          gdImageCreateFromPngSource is called to load a PNG from a data
          source other than a file. Usage is very similar to the
          gdImageCreateFromPng function, except that the programmer
          provides a custom data source.
          
          The programmer must write an input function which accepts a
          context pointer, a buffer, and a number of bytes to be read as
          arguments. This function must read the number of bytes
          requested, unless the end of the file has been reached, in
          which case the function should return zero, or an error has
          occurred, in which case the function should return -1. The
          programmer then creates a gdSource structure and sets the
          source pointer to the input function and the context pointer to
          any value which is useful to the programmer.
          
          The example below implements gdImageCreateFromPng by creating a
          custom data source and invoking gdImageCreateFromPngSource.
          

static int freadWrapper(void *context, char *buf, int len);

gdImagePtr gdImageCreateFromPng(FILE *in)
{
        gdSource s;
        s.source = freadWrapper;
        s.context = in;
        return gdImageCreateFromPngSource(&s);
}

static int freadWrapper(void *context, char *buf, int len)
{
        int got = fread(buf, 1, len, (FILE *) context);
        return got;
}

   gdImageCreateFromGd(FILE *in) _(FUNCTION)_
          gdImageCreateFromGdCtx(gdIOCtx *in) _(FUNCTION)_
          
          
          gdImageCreateFromGd is called to load images from gd format
          files. Invoke gdImageCreateFromGd with an already opened
          pointer to a file containing the desired image in the gd file
          format, which is specific to gd and intended for very fast
          loading. (It is _not_ intended for compression; for
          compression, use PNG.) gdImageCreateFromGd returns a gdImagePtr
          to the new image, or NULL if unable to load the image (most
          often because the file is corrupt or does not contain a gd
          format image). gdImageCreateFromGd does _not_ close the file.
          You can inspect the sx and sy members of the image to determine
          its size. The image must eventually be destroyed using
          gdImageDestroy().
          

... inside a function ...
gdImagePtr im;
FILE *in;
in = fopen("mygd.gd", "rb");
im = gdImageCreateFromGd(in);
fclose(in);
/* ... Use the image ... */
gdImageDestroy(im);

   gdImageCreateFromGd2(FILE *in) _(FUNCTION)_
          gdImageCreateFromGd2Ctx(gdIOCtx *in) _(FUNCTION)_
          
          
          gdImageCreateFromGd2 is called to load images from gd2 format
          files. Invoke gdImageCreateFromGd2 with an already opened
          pointer to a file containing the desired image in the gd2 file
          format, which is specific to gd2 and intended for fast loading
          of parts of large images. (It is a compressed format, but
          generally not as good a LZW compression). gdImageCreateFromGd
          returns a gdImagePtr to the new image, or NULL if unable to
          load the image (most often because the file is corrupt or does
          not contain a gd format image). gdImageCreateFromGd2 does _not_
          close the file. You can inspect the sx and sy members of the
          image to determine its size. The image must eventually be
          destroyed using gdImageDestroy().
          

... inside a function ...
gdImagePtr im;
FILE *in;
in = fopen("mygd.gd2", "rb");
im = gdImageCreateFromGd2(in);
fclose(in);
/* ... Use the image ... */
gdImageDestroy(im);

   gdImageCreateFromGd2Part(FILE *in, int srcX, int srcY, int w, int h)
          _(FUNCTION)_
          gdImageCreateFromGd2PartCtx(gdIOCtx *in) _(FUNCTION)_
          
          
          gdImageCreateFromGd2Part is called to load parts of images from
          gd2 format files. Invoked in the same way as
          gdImageCreateFromGd2, but with extra parameters indicating the
          source (x, y) and width/height of the desired image.
          gdImageCreateFromGd2Part returns a gdImagePtr to the new image,
          or NULL if unable to load the image. The image must eventually
          be destroyed using gdImageDestroy().
          
   gdImageCreateFromXbm(FILE *in) _(FUNCTION)_
          gdImageCreateFromXbm is called to load images from X bitmap
          format files. Invoke gdImageCreateFromXbm with an already
          opened pointer to a file containing the desired image.
          gdImageCreateFromXbm returns a gdImagePtr to the new image, or
          NULL if unable to load the image (most often because the file
          is corrupt or does not contain an X bitmap format image).
          gdImageCreateFromXbm does _not_ close the file. You can inspect
          the sx and sy members of the image to determine its size. The
          image must eventually be destroyed using gdImageDestroy().
          

... inside a function ...
gdImagePtr im;
FILE *in;
in = fopen("myxbm.xbm", "rb");
im = gdImageCreateFromXbm(in);
fclose(in);
/* ... Use the image ... */
gdImageDestroy(im);

   gdImageCreateFromXpm(FILE *in) _(FUNCTION)_
          gdImageCreateFromXbm is called to load images from XPM X Window
          System color bitmap format files. This function is available
          only if HAVE_XPM is selected in the Makefile and the Xpm
          library is linked with the application. Invoke
          gdImageCreateFromXpm with an already opened pointer to a file
          containing the desired image. gdImageCreateFromXpm returns a
          gdImagePtr to the new image, or NULL if unable to load the
          image (most often because the file is corrupt or does not
          contain an XPM bitmap format image). gdImageCreateFromXpm does
          _not_ close the file. You can inspect the sx and sy members of
          the image to determine its size. The image must eventually be
          destroyed using gdImageDestroy().
          

... inside a function ...
gdImagePtr im;
FILE *in;
in = fopen("myxpm.xpm", "rb");
im = gdImageCreateFromXpm(in);
fclose(in);
/* ... Use the image ... */
gdImageDestroy(im);

   gdImageDestroy(gdImagePtr im) _(FUNCTION)_
          gdImageDestroy is used to free the memory associated with an
          image. It is important to invoke gdImageDestroy before exiting
          your program or assigning a new image to a gdImagePtr variable.
          

... inside a function ...
gdImagePtr im;
im = gdImageCreate(10, 10);
/* ... Use the image ... */
/* Now destroy it */
gdImageDestroy(im);

   void gdImagePng(gdImagePtr im, FILE *out) _(FUNCTION)_
          gdImagePng outputs the specified image to the specified file in
          PNG format. The file must be open for writing. Under MSDOS and
          all versions of Windows, it is important to use "wb" as opposed
          to simply "w" as the mode when opening the file, and under Unix
          there is no penalty for doing so. gdImagePng does _not_ close
          the file; your code must do so.
          

... inside a function ...
gdImagePtr im;
int black, white;
FILE *out;
/* Create the image */
im = gdImageCreate(100, 100);
/* Allocate background */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Allocate drawing color */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Draw rectangle */
gdImageRectangle(im, 0, 0, 99, 99, black);
/* Open output file in binary mode */
out = fopen("rect.png", "wb");
/* Write PNG */
gdImagePng(im, out);
/* Close file */
fclose(out);
/* Destroy image */
gdImageDestroy(im);

   void* gdImagePngPtr(gdImagePtr im, int *size) _(FUNCTION)_
          Identical to gdImagePng except that it returns a pointer to a
          memory area with the PNG data. This memory must be freed by the
          caller when it is no longer needed. The 'size' parameter
          received the total size of the block of memory.
          
   gdImagePngToSink(gdImagePtr im, gdSinkPtr out) _(FUNCTION)_
          gdImagePngToSink is called to write a PNG to a data "sink"
          (destination) other than a file. Usage is very similar to the
          gdImagePng function, except that the programmer provides a
          custom data sink.
          
          The programmer must write an output function which accepts a
          context pointer, a buffer, and a number of bytes to be written
          as arguments. This function must write the number of bytes
          requested and return that number, unless an error has occurred,
          in which case the function should return -1. The programmer
          then creates a gdSink structure and sets the sink pointer to
          the output function and the context pointer to any value which
          is useful to the programmer.
          
          The example below implements gdImagePng by creating a custom
          data source and invoking gdImagePngFromSink.
          

static int stdioSink(void *context, char *buffer, int len)
{
        return fwrite(buffer, 1, len, (FILE *) context);
}

void gdImagePng(gdImagePtr im, FILE *out)
{
        gdSink mySink;
        mySink.context = (void *) out;
        mySink.sink = stdioSink;
        gdImagePngToSink(im, &mySink);
}

   void gdImageGd(gdImagePtr im, FILE *out) _(FUNCTION)_
          gdImageGd outputs the specified image to the specified file in
          the gd image format. The file must be open for writing. Under
          MSDOS and all versions of Windows, it is important to use "wb"
          as opposed to simply "w" as the mode when opening the file, and
          under Unix there is no penalty for doing so. gdImagePng does
          _not_ close the file; your code must do so.
          
          The gd image format is intended for fast reads and writes of
          images your program will need frequently to build other images.
          It is _not_ a compressed format, and is not intended for
          general use.
          

... inside a function ...
gdImagePtr im;
int black, white;
FILE *out;
/* Create the image */
im = gdImageCreate(100, 100);
/* Allocate background */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Allocate drawing color */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Draw rectangle */
gdImageRectangle(im, 0, 0, 99, 99, black);
/* Open output file in binary mode */
out = fopen("rect.gd", "wb");
/* Write gd format file */
gdImageGd(im, out);
/* Close file */
fclose(out);
/* Destroy image */
gdImageDestroy(im);

   void* gdImageGdPtr(gdImagePtr im, int *size) _(FUNCTION)_
          Identical to gdImageGd except that it returns a pointer to a
          memory area with the GD data. This memory must be freed by the
          caller when it is no longer needed. The 'size' parameter
          received the total size of the block of memory.
          
   void gdImageGd2(gdImagePtr im, FILE *out, int chunkSize, int fmt)
          _(FUNCTION)_
          gdImageGd2 outputs the specified image to the specified file in
          the gd2 image format. The file must be open for writing. Under
          MSDOS and all versions of Windows, it is important to use "wb"
          as opposed to simply "w" as the mode when opening the file, and
          under Unix there is no penalty for doing so. gdImageGd2 does
          _not_ close the file; your code must do so.
          
          The gd2 image format is intended for fast reads and writes of
          parts of images. It is a compressed format, and well suited to
          retrieving smll sections of much larger images. The third and
          fourth parameters are the 'chunk size' and format
          resposectively.
          
          The file is stored as a series of compressed subimages, and the
          _Chunk Size_ determines the sub-image size - a value of zero
          causes the GD library to use the default.
          
          It is also possible to store GD2 files in an uncompressed
          format, in which case the fourth parameter should be
          GD2_FMT_RAW.
          

... inside a function ...
gdImagePtr im;
int black, white;
FILE *out;
/* Create the image */
im = gdImageCreate(100, 100);
/* Allocate background */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Allocate drawing color */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Draw rectangle */
gdImageRectangle(im, 0, 0, 99, 99, black);
/* Open output file in binary mode */
out = fopen("rect.gd", "wb");
/* Write gd2 format file */
gdImageGd2(im, out, 0, GD2_FMT_COMPRESSED);
/* Close file */
fclose(out);
/* Destroy image */
gdImageDestroy(im);

   void* gdImageGd2Ptr(gdImagePtr im, int chunkSize, int fmt, int *size)
          _(FUNCTION)_
          Identical to gdImageGd2 except that it returns a pointer to a
          memory area with the GD2 data. This memory must be freed by the
          caller when it is no longer needed. The 'size' parameter
          received the total size of the block of memory.
          
  Drawing Functions
  
   void gdImageSetPixel(gdImagePtr im, int x, int y, int color)
          _(FUNCTION)_
          gdImageSetPixel sets a pixel to a particular color index.
          Always use this function or one of the other drawing functions
          to access pixels; do not access the pixels of the gdImage
          structure directly.
          

... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Set a pixel near the center. */
gdImageSetPixel(im, 50, 50, white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageLine(gdImagePtr im, int x1, int y1, int x2, int y2, int
          color) _(FUNCTION)_
          gdImageLine is used to draw a line between two endpoints (x1,y1
          and x2, y2). The line is drawn using the color index specified.
          Note that the color index can be an actual color returned by
          gdImageColorAllocate or one of gdStyled, gdBrushed or
          gdStyledBrushed.
          

... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a line from the upper left corner to the lower right corner. */
gdImageLine(im, 0, 0, 99, 99, white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageDashedLine(gdImagePtr im, int x1, int y1, int x2, int y2,
          int color) _(FUNCTION)_
          gdImageDashedLine is provided _solely for backwards
          compatibility _with gd 1.0. New programs should draw dashed
          lines using the normal gdImageLine function and the new
          gdImageSetStyle function.
          
          gdImageDashedLine is used to draw a dashed line between two
          endpoints (x1,y1 and x2, y2). The line is drawn using the color
          index specified. The portions of the line that are not drawn
          are left transparent so the background is visible.
          

... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a dashed line from the upper left corner to the lower right corner. */
gdImageDashedLine(im, 0, 0, 99, 99);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImagePolygon(gdImagePtr im, gdPointPtr points, int pointsTotal,
          int color) _(FUNCTION)_
          gdImagePolygon is used to draw a polygon with the verticies (at
          least 3) specified, using the color index specified. See also
          gdImageFilledPolygon.
          

... inside a function ...
gdImagePtr im;
int black;
int white;
/* Points of polygon */
gdPoint points[3];
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a triangle. */
points[0].x = 50;
points[0].y = 0;
points[1].x = 99;
points[1].y = 99;
points[2].x = 0;
points[2].y = 99;
gdImagePolygon(im, points, 3, white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageRectangle(gdImagePtr im, int x1, int y1, int x2, int y2,
          int color) _(FUNCTION)_
          gdImageRectangle is used to draw a rectangle with the two
          corners (upper left first, then lower right) specified, using
          the color index specified.
          

... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a rectangle occupying the central area. */
gdImageRectangle(im, 25, 25, 74, 74, white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageFilledPolygon(gdImagePtr im, gdPointPtr points, int
          pointsTotal, int color) _(FUNCTION)_
          gdImageFilledPolygon is used to fill a polygon with the
          verticies (at least 3) specified, using the color index
          specified. See also gdImagePolygon.
          

... inside a function ...
gdImagePtr im;
int black;
int white;
int red;
/* Points of polygon */
gdPoint points[3];
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Allocate the color red. */
red = gdImageColorAllocate(im, 255, 0, 0);
/* Draw a triangle. */
points[0].x = 50;
points[0].y = 0;
points[1].x = 99;
points[1].y = 99;
points[2].x = 0;
points[2].y = 99;
/* Paint it in white */
gdImageFilledPolygon(im, points, 3, white);
/* Outline it in red; must be done second */
gdImagePolygon(im, points, 3, red);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageFilledRectangle(gdImagePtr im, int x1, int y1, int x2, int
          y2, int color) _(FUNCTION)_
          gdImageFilledRectangle is used to draw a solid rectangle with
          the two corners (upper left first, then lower right) specified,
          using the color index specified.
          

... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = int gdImageColorAllocate(im, 255, 255, 255);
/* Draw a filled rectangle occupying the central area. */
gdImageFilledRectangle(im, 25, 25, 74, 74, white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageArc(gdImagePtr im, int cx, int cy, int w, int h, int s,
          int e, int color) _(FUNCTION)_
          gdImageArc is used to draw a partial ellipse centered at the
          given point, with the specified width and height in pixels. The
          arc begins at the position in degrees specified by s and ends
          at the position specified by e. The arc is drawn in the color
          specified by the last argument. A circle can be drawn by
          beginning from 0 degrees and ending at 360 degrees, with width
          and height being equal. e must be greater than s. Values
          greater than 360 are interpreted modulo 360.
          

... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 50);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Inscribe an ellipse in the image. */
gdImageArc(im, 50, 25, 98, 48, 0, 360, white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageFillToBorder(gdImagePtr im, int x, int y, int border, int
          color) _(FUNCTION)_
          gdImageFillToBorder floods a portion of the image with the
          specified color, beginning at the specified point and stopping
          at the specified border color. For a way of flooding an area
          defined by the color of the starting point, see gdImageFill.
          
          The border color _cannot_ be a special color such as gdTiled;
          it must be a proper solid color. The fill color can be,
          however.
          
          Note that gdImageFillToBorder is recursive. It is not the most
          naive implementation possible, and the implementation is
          expected to improve, but there will always be degenerate cases
          in which the stack can become very deep. This can be a problem
          in MSDOS and MS Windows 3.1 environments. (Of course, in a Unix
          or Windows 95/98/NT environment with a proper stack, this is
          not a problem at all.)
          

... inside a function ...
gdImagePtr im;
int black;
int white;
int red;
im = gdImageCreate(100, 50);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Allocate the color red. */
red = gdImageColorAllocate(im, 255, 0, 0);
/* Inscribe an ellipse in the image. */
gdImageArc(im, 50, 25, 98, 48, 0, 360, white);
/* Flood-fill the ellipse. Fill color is red, border color is
        white (ellipse). */
gdImageFillToBorder(im, 50, 50, white, red);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageFill(gdImagePtr im, int x, int y, int color) _(FUNCTION)_
          gdImageFill floods a portion of the image with the specified
          color, beginning at the specified point and flooding the
          surrounding region of the same color as the starting point. For
          a way of flooding a region defined by a specific border color
          rather than by its interior color, see gdImageFillToBorder.
          
          The fill color can be gdTiled, resulting in a tile fill using
          another image as the tile. However, the tile image cannot be
          transparent. If the image you wish to fill with has a
          transparent color index, call gdImageTransparent on the tile
          image and set the transparent color index to -1 to turn off its
          transparency.
          
          Note that gdImageFill is recursive. It is not the most naive
          implementation possible, and the implementation is expected to
          improve, but there will always be degenerate cases in which the
          stack can become very deep. This can be a problem in MSDOS and
          MS Windows environments. (Of course, in a Unix or Windows
          95/98/NT environment with a proper stack, this is not a problem
          at all.)
          

... inside a function ...
gdImagePtr im;
int black;
int white;
int red;
im = gdImageCreate(100, 50);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Allocate the color red. */
red = gdImageColorAllocate(im, 255, 0, 0);
/* Inscribe an ellipse in the image. */
gdImageArc(im, 50, 25, 98, 48, 0, 360, white);
/* Flood-fill the ellipse. Fill color is red, and will replace the
        black interior of the ellipse. */
gdImageFill(im, 50, 50, red);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

   void gdImageSetBrush(gdImagePtr im, gdImagePtr brush) _(FUNCTION)_
          A "brush" is an image used to draw wide, shaped strokes in
          another image. Just as a paintbrush is not a single point, a
          brush image need not be a single pixel. _Any_ gd image can be
          used as a brush, and by setting the transparent color index of
          the brush image with gdImageColorTransparent, a brush of any
          shape can be created. All line-drawing functions, such as
          gdImageLine and gdImagePolygon, will use the current brush if
          the special "color" gdBrushed or gdStyledBrushed is used when
          calling them.
          
          gdImageSetBrush is used to specify the brush to be used in a
          particular image. You can set any image to be the brush. If the
          brush image does not have the same color map as the first
          image, any colors missing from the first image will be
          allocated. If not enough colors can be allocated, the closest
          colors already available will be used. This allows arbitrary
          PNGs to be used as brush images. It also means, however, that
          you should not set a brush unless you will actually use it; if
          you set a rapid succession of different brush images, you can
          quickly fill your color map, and the results will not be
          optimal.
          
          You need not take any special action when you are finished with
          a brush. As for any other image, if you will not be using the
          brush image for any further purpose, you should call
          gdImageDestroy. You must not use the color gdBrushed if the
          current brush has been destroyed; you can of course set a new
          brush to replace it.
          

... inside a function ...
gdImagePtr im, brush;
FILE *in;
int black;
im = gdImageCreate(100, 100);
/* Open the brush PNG. For best results, portions of the
        brush that should be transparent (ie, not part of the
        brush shape) should have the transparent color index. */
in = fopen("star.png", "rb");
brush = gdImageCreateFromPng(in);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
gdImageSetBrush(im, brush);
/* Draw a line from the upper left corner to the lower right corner
        using the brush. */
gdImageLine(im, 0, 0, 99, 99, gdBrushed);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);
/* Destroy the brush image */
gdImageDestroy(brush);

   void gdImageSetTile(gdImagePtr im, gdImagePtr tile) _(FUNCTION)_
          A "tile" is an image used to fill an area with a repeated
          pattern. _Any_ gd image can be used as a tile, and by setting
          the transparent color index of the tile image with
          gdImageColorTransparent, a tile that allows certain parts of
          the underlying area to shine through can be created. All
          region-filling functions, such as gdImageFill and
          gdImageFilledPolygon, will use the current tile if the special
          "color" gdTiled is used when calling them.
          
          gdImageSetTile is used to specify the tile to be used in a
          particular image. You can set any image to be the tile. If the
          tile image does not have the same color map as the first image,
          any colors missing from the first image will be allocated. If
          not enough colors can be allocated, the closest colors already
          available will be used. This allows arbitrary PNGs to be used
          as tile images. It also means, however, that you should not set
          a tile unless you will actually use it; if you set a rapid
          succession of different tile images, you can quickly fill your
          color map, and the results will not be optimal.
          
          You need not take any special action when you are finished with
          a tile. As for any other image, if you will not be using the
          tile image for any further purpose, you should call
          gdImageDestroy. You must not use the color gdTiled if the
          current tile has been destroyed; you can of course set a new
          tile to replace it.
          

... inside a function ...
gdImagePtr im, tile;
FILE *in;
int black;
im = gdImageCreate(100, 100);
/* Open the tile PNG. For best results, portions of the
        tile that should be transparent (ie, allowing the
        background to shine through) should have the transparent
        color index. */
in = fopen("star.png", "rb");
tile = gdImageCreateFromPng(in);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
gdImageSetTile(im, tile);
/* Fill an area using the tile. */
gdImageFilledRectangle(im, 25, 25, 75, 75, gdTiled);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);
/* Destroy the tile image */
gdImageDestroy(tile);

   void gdImageSetStyle(gdImagePtr im, int *style, int styleLength)
          _(FUNCTION)_
          It is often desirable to draw dashed lines, dotted lines, and
          other variations on a broken line. gdImageSetStyle can be used
          to set any desired series of colors, including a special color
          that leaves the background intact, to be repeated during the
          drawing of a line.
          
          To use gdImageSetStyle, create an array of integers and assign
          them the desired series of color values to be repeated. You can
          assign the special color value gdTransparent to indicate that
          the existing color should be left unchanged for that particular
          pixel (allowing a dashed line to be attractively drawn over an
          existing image).
          
          Then, to draw a line using the style, use the normal
          gdImageLine function with the special color value gdStyled.
          
          As of version 1.1.1, the style array is copied when you set the
          style, so you need not be concerned with keeping the array
          around indefinitely. This should not break existing code that
          assumes styles are not copied.
          
          You can also combine styles and brushes to draw the brush image
          at intervals instead of in a continuous stroke. When creating a
          style for use with a brush, the style values are interpreted
          differently: zero (0) indicates pixels at which the brush
          should not be drawn, while one (1) indicates pixels at which
          the brush should be drawn. To draw a styled, brushed line, you
          must use the special color value gdStyledBrushed. For an
          example of this feature in use, see gddemo.c (provided in the
          distribution).
          

gdImagePtr im;
int styleDotted[2], styleDashed[6];
FILE *in;
int black;
int red;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
red = gdImageColorAllocate(im, 255, 0, 0);
/* Set up dotted style. Leave every other pixel alone. */
styleDotted[0] = red;
styleDotted[1] = gdTransparent;
/* Set up dashed style. Three on, three off. */
styleDashed[0] = red;
styleDashed[1] = red;
styleDashed[2] = red;
styleDashed[3] = gdTransparent;
styleDashed[4] = gdTransparent;
styleDashed[5] = gdTransparent;
/* Set dotted style. Note that we have to specify how many pixels are
        in the style! */
gdImageSetStyle(im, styleDotted, 2);
/* Draw a line from the upper left corner to the lower right corner. */
gdImageLine(im, 0, 0, 99, 99, gdStyled);
/* Now the dashed line. */
gdImageSetStyle(im, styleDashed, 6);
gdImageLine(im, 0, 99, 0, 99, gdStyled);

/* ... Do something with the image, such as saving it to a file ... */

/* Destroy it */
gdImageDestroy(im);

  Query Functions
  
        int gdImageBlue(gdImagePtr im, int color) _(MACRO)_
                gdImageBlue is a macro which returns the blue component
                of the specified color index. Use this macro rather than
                accessing the structure members directly.
                
        int gdImageGetPixel(gdImagePtr im, int x, int y) _(FUNCTION)_
                gdImageGetPixel() retrieves the color index of a
                particular pixel. Always use this function to query
                pixels; do not access the pixels of the gdImage structure
                directly.
                

... inside a function ...
FILE *in;
gdImagePtr im;
int c;
in = fopen("mypng.png", "rb");
im = gdImageCreateFromPng(in);
fclose(in);
c = gdImageGetPixel(im, gdImageSX(im) / 2, gdImageSY(im) / 2);
printf("The value of the center pixel is %d; RGB values are %d,%d,%d\n",
        c, im->red[c], im->green[c], im->blue[c]);
gdImageDestroy(im);

        int gdImageBoundsSafe(gdImagePtr im, int x, int y) _(FUNCTION)_
                gdImageBoundsSafe returns true (1) if the specified point
                is within the bounds of the image, false (0) if not. This
                function is intended primarily for use by those who wish
                to add functions to gd. All of the gd drawing functions
                already clip safely to the edges of the image.
                

... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 100);
if (gdImageBoundsSafe(im, 50, 50)) {
        printf("50, 50 is within the image bounds\n");
} else {
        printf("50, 50 is outside the image bounds\n");
}
gdImageDestroy(im);

        int gdImageGreen(gdImagePtr im, int color) _(MACRO)_
                gdImageGreen is a macro which returns the green component
                of the specified color index. Use this macro rather than
                accessing the structure members directly.
                
        int gdImageRed(gdImagePtr im, int color) _(MACRO)_
                gdImageRed is a macro which returns the red component of
                the specified color index. Use this macro rather than
                accessing the structure members directly.
                
        int gdImageSX(gdImagePtr im) _(MACRO)_
                gdImageSX is a macro which returns the width of the image
                in pixels. Use this macro rather than accessing the
                structure members directly.
                
        int gdImageSY(gdImagePtr im) _(MACRO)_
                gdImageSY is a macro which returns the height of the
                image in pixels. Use this macro rather than accessing the
                structure members directly.
                
  Fonts and text-handling functions
  
        void gdImageChar(gdImagePtr im, gdFontPtr font, int x, int y, int
                c, int color) _(FUNCTION)_
                gdImageChar is used to draw single characters on the
                image. (To draw multiple characters, use gdImageString or
                gdImageString16. See also gdImageStringTTF, new with
                gd-1.6.2.) The second argument is a pointer to a font
                definition structure; five fonts are provided with gd,
                gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge,
                and gdFontGiant. You must include the files "gdfontt.h",
                "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h"
                respectively and (if you are not using a library-based
                approach) link with the corresponding .c files to use the
                provided fonts. The character specified by the fifth
                argument is drawn from left to right in the specified
                color. (See gdImageCharUp for a way of drawing vertical
                text.) Pixels not set by a particular character retain
                their previous color.
                

#include "gd.h"
#include "gdfontl.h"
... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a character. */
gdImageChar(im, gdFontLarge, 0, 0, 'Q', white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        void gdImageCharUp(gdImagePtr im, gdFontPtr font, int x, int y,
                int c, int color) _(FUNCTION)_
                gdImageCharUp is used to draw single characters on the
                image, rotated 90 degrees. (To draw multiple characters,
                use gdImageStringUp or gdImageStringUp16.) The second
                argument is a pointer to a font definition structure;
                five fonts are provided with gd, gdFontTiny, gdFontSmall,
                gdFontMediumBold, gdFontLarge, and gdFontGiant. You must
                include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h",
                "gdfontl.h" and "gdfontg.h" respectively and (if you are
                not using a library-based approach) link with the
                corresponding .c files to use the provided fonts. The
                character specified by the fifth argument is drawn from
                bottom to top, rotated at a 90-degree angle, in the
                specified color. (See gdImageChar for a way of drawing
                horizontal text.) Pixels not set by a particular
                character retain their previous color.
                

#include "gd.h"
#include "gdfontl.h"
... inside a function ...
gdImagePtr im;
int black;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a character upwards so it rests against the top of the image. */
gdImageCharUp(im, gdFontLarge,
        0, gdFontLarge->h, 'Q', white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        void gdImageString(gdImagePtr im, gdFontPtr font, int x, int y,
                unsigned char *s, int color) _(FUNCTION)_
                gdImageString is used to draw multiple characters on the
                image. (To draw single characters, use gdImageChar.) The
                second argument is a pointer to a font definition
                structure; five fonts are provided with gd, gdFontTiny,
                gdFontSmall, gdFontMediumBold, gdFontLarge, and
                gdFontGiant. You must include the files "gdfontt.h",
                "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h"
                respectively and (if you are not using a library-based
                approach) link with the corresponding .c files to use the
                provided fonts. The null-terminated C string specified by
                the fifth argument is drawn from left to right in the
                specified color. (See gdImageStringUp for a way of
                drawing vertical text. See also gdImageStringTTF, new
                with gd-1.6.2.) Pixels not set by a particular character
                retain their previous color.
                

#include "gd.h"
#include "gdfontl.h"
#include <string.h>
... inside a function ...
gdImagePtr im;
int black;
int white;
/* String to draw. */
char *s = "Hello.";
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a centered string. */
gdImageString(im, gdFontLarge,
        im->w / 2 - (strlen(s) * gdFontLarge->w / 2),
        im->h / 2 - gdFontLarge->h / 2,
        s, white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        void gdImageString16(gdImagePtr im, gdFontPtr font, int x, int y,
                unsigned short *s, int color) _(FUNCTION)_
                gdImageString is used to draw multiple 16-bit characters
                on the image. (To draw single characters, use
                gdImageChar.) The second argument is a pointer to a font
                definition structure; five fonts are provided with gd,
                gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge,
                and gdFontGiant. You must include the files "gdfontt.h",
                "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h"
                respectively and (if you are not using a library-based
                approach) link with the corresponding .c files to use the
                provided fonts. The null-terminated string of characters
                represented as 16-bit unsigned short integers specified
                by the fifth argument is drawn from left to right in the
                specified color. (See gdImageStringUp16 for a way of
                drawing vertical text.) Pixels not set by a particular
                character retain their previous color.
                
                This function was added in gd1.3 to provide a means of
                rendering fonts with more than 256 characters for those
                who have them. A more frequently used routine is
                gdImageString.
                
        void gdImageStringUp(gdImagePtr im, gdFontPtr font, int x, int y,
                unsigned char *s, int color) _(FUNCTION)_
                gdImageStringUp is used to draw multiple characters on
                the image, rotated 90 degrees. (To draw single
                characters, use gdImageCharUp.) The second argument is a
                pointer to a font definition structure; five fonts are
                provided with gd, gdFontTiny, gdFontSmall,
                gdFontMediumBold, gdFontLarge, and gdFontGiant. You must
                include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h",
                "gdfontl.h" and "gdfontg.h" respectively and (if you are
                not using a library-based approach) link with the
                corresponding .c files to use the provided fonts.The
                null-terminated C string specified by the fifth argument
                is drawn from bottom to top (rotated 90 degrees) in the
                specified color. (See gdImageString for a way of drawing
                horizontal text.) Pixels not set by a particular
                character retain their previous color.
                

#include "gd.h"
#include "gdfontl.h"
#include <string.h>
... inside a function ...
gdImagePtr im;
int black;
int white;
/* String to draw. */
char *s = "Hello.";
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a centered string going upwards. Axes are reversed,
        and Y axis is decreasing as the string is drawn. */
gdImageStringUp(im, gdFontLarge,
        im->w / 2 - gdFontLarge->h / 2,
        im->h / 2 + (strlen(s) * gdFontLarge->w / 2),
        s, white);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        void gdImageStringUp16(gdImagePtr im, gdFontPtr font, int x, int
                y, unsigned short *s, int color) _(FUNCTION)_
                gdImageString is used to draw multiple 16-bit characters
                vertically on the image. (To draw single characters, use
                gdImageChar.) The second argument is a pointer to a font
                definition structure; five fonts are provided with gd,
                gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge,
                and gdFontGiant. You must include the files "gdfontt.h",
                "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h"
                respectively and (if you are not using a library-based
                approach) link with the corresponding .c files to use the
                provided fonts. The null-terminated string of characters
                represented as 16-bit unsigned short integers specified
                by the fifth argument is drawn from bottom to top in the
                specified color. (See gdImageStringUp16 for a way of
                drawing horizontal text.) Pixels not set by a particular
                character retain their previous color.
                
                This function was added in gd1.3 to provide a means of
                rendering fonts with more than 256 characters for those
                who have them. A more frequently used routine is
                gdImageStringUp.
                
        char *gdImageStringTTF(gdImagePtr im, int *brect, int fg, char
                *fontname, double ptsize, double angle, int x, int y,
                char *string) _(FUNCTION)_
                gdImageStringTTF is draws a string of anti-aliased
                characters on the image using the FreeType library to
                print from user-supplied TrueType fonts. _We do not
                provide TrueType fonts. Obtaining them is entirely up to
                you._ The string is anti-aliased, meaning that there
                should be less "jaggies." The fontname is the full
                pathname to a TrueType font file. The string may be
                arbitrarily scaled (ptsize) and rotated (angle in
                radians).
                
                The user-supplied int brect[8] array is filled on return
                from gdImageStringTTF with the 8 elements representing
                the 4 corner coordinates of the bounding rectangle.
                0 lower left corner, X position
                lower left corner, Y position
                lower right corner, X position
                3 lower right corner, Y position
                4 upper right corner, X position
                5 upper right corner, Y position
                6 upper left corner, X position
                7 upper left corner, Y position
                
                The points are relative to the text regardless of the
                angle, so "upper left" means in the top left-hand corner
                seeing the text horizontally.
                
                Use a NULL gdImagePtr to get the bounding rectangle
                without rendering. This is a relatively cheap operation
                if followed by a rendering of the same string, because of
                the caching of the partial rendering during bounding
                rectangle calculation.
                
                The string is rendered in the color indicated by the gf
                color index. Use the negative of the desired color index
                to disable anti-aliasing.
                
                The string may contain UTF-8 sequences like: "&#192;"
                
                gdImageStringTTF will return a null char* on success, or
                an error string on failure.
                

#include "gd.h"
#include <string.h>
... inside a function ...
gdImagePtr im;
int black;
int white;
int brect[8];
int x, y;
char *err;

char *s = "Hello."; /* String to draw. */
double sz = 40.;
char *f = "/usr/local/share/ttf/Times.ttf";  /* User supplied font */

/* obtain brect so that we can size the image */
err = gdImageStringTTF(NULL,&brect[0],0,f,sz,0.,0,0,s);
if (err) {fprintf(stderr,err); return 1;}

/* create an image big enough for the string plus a little whitespace */
x = brect[2]-brect[6] + 6;
y = brect[3]-brect[7] + 6;
im = gdImageCreate(x,y);

/* Background color (first allocated) */
white = gdImageColorResolve(im, 255, 255, 255);
black = gdImageColorResolve(im, 0, 0, 0);

/* render the string, offset origin to center string*/
/* note that we use top-left coordinate for adjustment
 * since gd origin is in top-left with y increasing downwards. */
x = 3 - brect[6];
y = 3 - brect[7];
err = gdImageStringTTF(im,&brect[0],black,f,sz,0.0,x,y,s);
if (err) {fprintf(stderr,err); return 1;}

/* Write img to stdout */
gdImagePng(im, stdout);

/* Destroy it */
gdImageDestroy(im);

  Color-handling functions
  
        int gdImageColorAllocate(gdImagePtr im, int r, int g, int b)
                _(FUNCTION)_
                gdImageColorAllocate finds the first available color
                index in the image specified, sets its RGB values to
                those requested (255 is the maximum for each), and
                returns the index of the new color table entry. When
                creating a new image, the first time you invoke this
                function, you are setting the background color for that
                image.
                
                In the event that all gdMaxColors colors (256) have
                already been allocated, gdImageColorAllocate will return
                -1 to indicate failure. (This is not uncommon when
                working with existing PNG files that already use 256
                colors.) Note that gdImageColorAllocate does not check
                for existing colors that match your request; see
                gdImageColorExact and gdImageColorClosest for ways to
                locate existing colors that approximate the color desired
                in situations where a new color is not available. Also
                see gdImageColorResolve, new in gd-1.6.2.
                

... inside a function ...
gdImagePtr im;
int black;
int red;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color red. */
red = gdImageColorAllocate(im, 255, 0, 0);
/* Draw a dashed line from the upper left corner to the lower right corner. */
gdImageDashedLine(im, 0, 0, 99, 99, red);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        int gdImageColorClosest(gdImagePtr im, int r, int g, int b)
                _(FUNCTION)_
                gdImageColorClosest searches the colors which have been
                defined thus far in the image specified and returns the
                index of the color with RGB values closest to those of
                the request. (Closeness is determined by Euclidian
                distance, which is used to determine the distance in
                three-dimensional color space between colors.)
                
                If no colors have yet been allocated in the image,
                gdImageColorClosest returns -1.
                
                This function is most useful as a backup method for
                choosing a drawing color when an image already contains
                gdMaxColors (256) colors and no more can be allocated.
                (This is not uncommon when working with existing PNG
                files that already use many colors.) See
                gdImageColorExact for a method of locating exact matches
                only.
                

... inside a function ...
gdImagePtr im;
FILE *in;
int red;
/* Let's suppose that photo.png is a scanned photograph with
        many colors. */
in = fopen("photo.png", "rb");
im = gdImageCreateFromPng(in);
fclose(in);
/* Try to allocate red directly */
red = gdImageColorAllocate(im, 255, 0, 0);
/* If we fail to allocate red... */
if (red == (-1)) {
        /* Find the _closest_ color instead. */
        red = gdImageColorClosest(im, 255, 0, 0);
}
/* Draw a dashed line from the upper left corner to the lower right corner */
gdImageDashedLine(im, 0, 0, 99, 99, red);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        int gdImageColorExact(gdImagePtr im, int r, int g, int b)
                _(FUNCTION)_
                gdImageColorExact searches the colors which have been
                defined thus far in the image specified and returns the
                index of the first color with RGB values which exactly
                match those of the request. If no allocated color matches
                the request precisely, gdImageColorExact returns -1. See
                gdImageColorClosest for a way to find the color closest
                to the color requested.
                

... inside a function ...
gdImagePtr im;
int red;
in = fopen("photo.png", "rb");
im = gdImageCreateFromPng(in);
fclose(in);
/* The image may already contain red; if it does, we'll save a slot
        in the color table by using that color. */
/* Try to allocate red directly */
red = gdImageColorExact(im, 255, 0, 0);
/* If red isn't already present... */
if (red == (-1)) {
        /* Second best: try to allocate it directly. */
        red = gdImageColorAllocate(im, 255, 0, 0);
        /* Out of colors, so find the _closest_ color instead. */
        red = gdImageColorClosest(im, 255, 0, 0);
}
/* Draw a dashed line from the upper left corner to the lower right corner */
gdImageDashedLine(im, 0, 0, 99, 99, red);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        int gdImageColorResolve(gdImagePtr im, int r, int g, int b)
                _(FUNCTION)_
                gdImageColorResolve searches the colors which have been
                defined thus far in the image specified and returns the
                index of the first color with RGB values which exactly
                match those of the request. If no allocated color matches
                the request precisely, then gdImageColorResolve tries to
                allocate the exact color. If there is no space left in
                the color table then gdImageColorResolve returns the
                closest color (as in gdImageColorClosest). This function
                always returns an index of a color.
                

... inside a function ...
gdImagePtr im;
int red;
in = fopen("photo.png", "rb");
im = gdImageCreateFromPng(in);
fclose(in);
/* The image may already contain red; if it does, we'll save a slot
        in the color table by using that color. */
/* Get index of red, or color closest to red */
red = gdImageColorResolve(im, 255, 0, 0);
/* Draw a dashed line from the upper left corner to the lower right corner */
gdImageDashedLine(im, 0, 0, 99, 99, red);
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        int gdImageColorsTotal(gdImagePtr im) _(MACRO)_
                gdImageColorsTotal is a macro which returns the number of
                colors currently allocated in the image. Use this macro
                to obtain this information; do not access the structure
                directly.
                
        int gdImageColorRed(gdImagePtr im, int c) _(MACRO)_
                gdImageColorRed is a macro which returns the red portion
                of the specified color in the image. Use this macro to
                obtain this information; do not access the structure
                directly.
                
        int gdImageColorGreen(gdImagePtr im, int c) _(MACRO)_
                gdImageColorGreen is a macro which returns the green
                portion of the specified color in the image. Use this
                macro to obtain this information; do not access the
                structure directly.
                
        int gdImageColorBlue(gdImagePtr im, int c) _(MACRO)_
                gdImageColorBlue is a macro which returns the green
                portion of the specified color in the image. Use this
                macro to obtain this information; do not access the
                structure directly.
                
        int gdImageGetInterlaced(gdImagePtr im) _(MACRO)_
                gdImageGetInterlaced is a macro which returns true (1) if
                the image is interlaced, false (0) if not. Use this macro
                to obtain this information; do not access the structure
                directly. See gdImageInterlace for a means of interlacing
                images.
                
        int gdImageGetTransparent(gdImagePtr im) _(MACRO)_
                gdImageGetTransparent is a macro which returns the
                current transparent color index in the image. If there is
                no transparent color, gdImageGetTransparent returns -1.
                Use this macro to obtain this information; do not access
                the structure directly.
                
        void gdImageColorDeallocate(gdImagePtr im, int color) _(FUNCTION)_
                
                gdImageColorDeallocate marks the specified color as being
                available for reuse. It does not attempt to determine
                whether the color index is still in use in the image.
                After a call to this function, the next call to
                gdImageColorAllocate for the same image will set new RGB
                values for that color index, changing the color of any
                pixels which have that index as a result. If multiple
                calls to gdImageColorDeallocate are made consecutively,
                the lowest-numbered index among them will be reused by
                the next gdImageColorAllocate call.
                

... inside a function ...
gdImagePtr im;
int red, blue;
in = fopen("photo.png", "rb");
im = gdImageCreateFromPng(in);
fclose(in);
/* Look for red in the color table. */
red = gdImageColorExact(im, 255, 0, 0);
/* If red is present... */
if (red != (-1)) {
        /* Deallocate it. */
        gdImageColorDeallocate(im, red);
        /* Allocate blue, reusing slot in table.
                Existing red pixels will change color. */
        blue = gdImageColorAllocate(im, 0, 0, 255);
}
/* ... Do something with the image, such as saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

        void gdImageColorTransparent(gdImagePtr im, int color)
                _(FUNCTION)_
                gdImageColorTransparent sets the transparent color index
                for the specified image to the specified index. To
                indicate that there should be _no_ transparent color,
                invoke gdImageColorTransparent with a color index of -1.
                
                The color index used should be an index allocated by
                gdImageColorAllocate, whether explicitly invoked by your
                code or implicitly invoked by loading an image. In order
                to ensure that your image has a reasonable appearance
                when viewed by users who do not have transparent
                background capabilities, be sure to give reasonable RGB
                values to the color you allocate for use as a transparent
                color, _even though it will be transparent on systems
                that support transparency_.
                

... inside a function ...
gdImagePtr im;
int black;
FILE *in, *out;
in = fopen("photo.png", "rb");
im = gdImageCreateFromPng(in);
fclose(in);
/* Look for black in the color table and make it transparent. */
black = gdImageColorExact(im, 0, 0, 0);
/* If black is present... */
if (black != (-1)) {
        /* Make it transparent */
        gdImageColorTransparent(im, black);
}
/* Save the newly-transparent image back to the file */
out = fopen("photo.png", "wb");
gdImagePng(im, out);
fclose(out);
/* Destroy it */
gdImageDestroy(im);

  Copying and resizing functions
  
        void gdImageCopy(gdImagePtr dst, gdImagePtr src, int dstX, int
                dstY, int srcX, int srcY, int w, int h) _(FUNCTION)_
                gdImageCopy is used to copy a rectangular portion of one
                image to another image. (For a way of stretching or
                shrinking the image in the process, see
                gdImageCopyResized.)
                
                The dst argument is the destination image to which the
                region will be copied. The src argument is the source
                image from which the region is copied. The dstX and dstY
                arguments specify the point in the destination image to
                which the region will be copied. The srcX and srcY
                arguments specify the upper left corner of the region in
                the source image. The w and h arguments specify the width
                and height of the region.
                
                When you copy a region from one location in an image to
                another location in the same image, gdImageCopy will
                perform as expected unless the regions overlap, in which
                case the result is unpredictable.
                
                _Important note on copying between images:_ since
                different images do not necessarily have the same color
                tables, pixels are not simply set to the same color index
                values to copy them. gdImageCopy will attempt to find an
                identical RGB value in the destination image for each
                pixel in the copied portion of the source image by
                invoking gdImageColorExact. If such a value is not found,
                gdImageCopy will attempt to allocate colors as needed
                using gdImageColorAllocate. If both of these methods
                fail, gdImageCopy will invoke gdImageColorClosest to find
                the color in the destination image which most closely
                approximates the color of the pixel being copied.
                

... Inside a function ...
gdImagePtr im_in;
gdImagePtr im_out;
int x, y;
FILE *in;
FILE *out;
/* Load a small png to tile the larger one with */
in = fopen("small.png", "rb");
im_in = gdImageCreateFromPng(in);
fclose(in);
/* Make the output image four times as large on both axes */
im_out = gdImageCreate(im_in->sx * 4, im_in->sy * 4);
/* Now tile the larger image using the smaller one */
for (y = 0; (y < 4); y++) {
        for (x = 0; (x < 4); x++) {
                gdImageCopy(im_out, im_in,
                        x * im_in->sx, y * im_in->sy,
                        0, 0,
                        im_in->sx, im_in->sy);
        }
}
out = fopen("tiled.png", "wb");
gdImagePng(im_out, out);
fclose(out);
gdImageDestroy(im_in);
gdImageDestroy(im_out);

        void gdImageCopyResized(gdImagePtr dst, gdImagePtr src, int dstX,
                int dstY, int srcX, int srcY, int destW, int destH, int
                srcW, int srcH) _(FUNCTION)_
                gdImageCopyResized is used to copy a rectangular portion
                of one image to another image. The X and Y dimensions of
                the original region and the destination region can vary,
                resulting in stretching or shrinking of the region as
                appropriate. (For a simpler version of this function
                which does not deal with resizing, see gdImageCopy.)
                
                The dst argument is the destination image to which the
                region will be copied. The src argument is the source
                image from which the region is copied. The dstX and dstY
                arguments specify the point in the destination image to
                which the region will be copied. The srcX and srcY
                arguments specify the upper left corner of the region in
                the source image. The dstW and dstH arguments specify the
                width and height of the destination region. The srcW and
                srcH arguments specify the width and height of the source
                region and can differ from the destination size, allowing
                a region to be scaled during the copying process.
                
                When you copy a region from one location in an image to
                another location in the same image, gdImageCopy will
                perform as expected unless the regions overlap, in which
                case the result is unpredictable. If this presents a
                problem, create a scratch image in which to keep
                intermediate results.
                
                _Important note on copying between images:_ since images
                do not necessarily have the same color tables, pixels are
                not simply set to the same color index values to copy
                them. gdImageCopy will attempt to find an identical RGB
                value in the destination image for each pixel in the
                copied portion of the source image by invoking
                gdImageColorExact. If such a value is not found,
                gdImageCopy will attempt to allocate colors as needed
                using gdImageColorAllocate. If both of these methods
                fail, gdImageCopy will invoke gdImageColorClosest to find
                the color in the destination image which most closely
                approximates the color of the pixel being copied.
                

... Inside a function ...
gdImagePtr im_in;
gdImagePtr im_out;
int x, y;
FILE *in;
FILE *out;
/* Load a small png to expand in the larger one */
in = fopen("small.png", "rb");
im_in = gdImageCreateFromPng(in);
fclose(in);
/* Make the output image four times as large on both axes */
im_out = gdImageCreate(im_in->sx * 4, im_in->sy * 4);
/* Now copy the smaller image, but four times larger */
gdImageCopyResized(im_out, im_in, 0, 0, 0, 0,
        im_out->sx, im_out->sy,
        im_in->sx, im_in->sy);
out = fopen("large.png", "wb");
gdImagePng(im_out, out);
fclose(out);
gdImageDestroy(im_in);
gdImageDestroy(im_out);

        void gdImageCopyMerge(gdImagePtr dst, gdImagePtr src, int dstX,
                int dstY, int srcX, int srcY, int w, int h, int pct)
                _(FUNCTION)_
                gdImageCopyMerge is almost identical to gdImageCopy,
                except that it 'merges' the two images by an amount
                specified in the last parameter. If the last parameter is
                100, then it will function identically to gdImageCopy -
                the source image replaces the pixels in the destination.
                
                If, however, the _pct_ parameter is less than 100, then
                the two images are merged. With pct = 0, no action is
                taken.
                
                This feature is most useful to 'highlight' sections of an
                image by merging a solid color with pct = 50:
                

... Inside a function ...
gdImageCopyMerge(im_out, im_in, 100, 200, 0, 0, 30, 50, 50);

        void gdImageCopyMergeGray(gdImagePtr dst, gdImagePtr src, int
                dstX, int dstY, int srcX, int srcY, int w, int h, int
                pct) _(FUNCTION)_
                gdImageCopyMergeGray is almost identical to
                gdImageCopyMerge, except that when merging images it
                preserves the hue of the source by converting the
                destination pixels to grey scale before the copy
                operation.
                

... Inside a function ...
gdImageCopyMergeGray(im_out, im_in, 100, 200, 0, 0, 30, 50, 50);

        void gdImagePaletteCopy(gdImagePtr dst, gdImagePtr src)
                _(FUNCTION)_
                Copies a palette from one image to another, doing it's
                best to match the colors in the target image to the
                colors in the source palette.
                
  Miscellaneous Functions
  
              int gdImageCompare(gdImagePtr im1, gdImagePtr im2)
                      _(FUNCTION)_
                      gdImageCompare returns a bitmap indicating if the
                      two images are different. The members of the bitmap
                      are defined in gd.h, but the most important is
                      GD_CMP_IMAGE, which indicated that the images will
                      actually appear different when displayed. Other,
                      less important, differences relate to pallette
                      entries. Any difference in the transparent colour
                      is assumed to make images display differently, even
                      if the transparent colour is not used.
                      

... Inside a function ...
cmpMask = gdImageCompare(im1, im2);

              gdImageInterlace(gdImagePtr im, int interlace) _(FUNCTION)_
                      
                      gdImageInterlace is used to determine whether an
                      image should be stored in a linear fashion, in
                      which lines will appear on the display from first
                      to last, or in an interlaced fashion, in which the
                      image will "fade in" over several passes. By
                      default, images are not interlaced.
                      
                      A nonzero value for the interlace argument turns on
                      interlace; a zero value turns it off. Note that
                      interlace has no effect on other functions, and has
                      no meaning unless you save the image in PNG format;
                      the gd and xbm formats do not support interlace.
                      
                      When a PNG is loaded with gdImageCreateFromPng ,
                      interlace will be set according to the setting in
                      the PNG file.
                      
                      Note that many PNG viewers and web browsers do _not_
                      support interlace. However, the interlaced PNG
                      should still display; it will simply appear all at
                      once, just as other images do.
                      

gdImagePtr im;
FILE *out;
/* ... Create or load the image... */

/* Now turn on interlace */
gdImageInterlace(im, 1);
/* And open an output file */
out = fopen("test.png", "wb");
/* And save the image */
gdImagePng(im, out);
fclose(out);
gdImageDestroy(im);

  Constants
  
                    gdBrushed _(CONSTANT)_
                            Used in place of a color when invoking a
                            line-drawing function such as gdImageLine or
                            gdImageRectangle. When gdBrushed is used as
                            the color, the brush image set with
                            gdImageSetBrush is drawn in place of each
                            pixel of the line (the brush is usually
                            larger than one pixel, creating the effect of
                            a wide paintbrush). See also gdStyledBrushed
                            for a way to draw broken lines with a series
                            of distinct copies of an image.
                            
                    gdMaxColors_(CONSTANT)_
                            The constant 256. This is the maximum number
                            of colors in a PNG file according to the PNG
                            standard, and is also the maximum number of
                            colors in a gd image.
                            
                    gdStyled _(CONSTANT)_
                            Used in place of a color when invoking a
                            line-drawing function such as gdImageLine or
                            gdImageRectangle. When gdStyled is used as
                            the color, the colors of the pixels are drawn
                            successively from the style that has been set
                            with gdImageSetStyle. If the color of a pixel
                            is equal to gdTransparent, that pixel is not
                            altered. (This mechanism is completely
                            unrelated to the "transparent color" of the
                            image itself; see gdImageColorTransparent
                            gdImageColorTransparent for that mechanism.)
                            See also gdStyledBrushed.
                            
                    gdStyledBrushed _(CONSTANT)_
                            Used in place of a color when invoking a
                            line-drawing function such as gdImageLine or
                            gdImageRectangle. When gdStyledBrushed is
                            used as the color, the brush image set with
                            gdImageSetBrush is drawn at each pixel of the
                            line, providing that the style set with
                            gdImageSetStyle contains a nonzero value (OR
                            gdTransparent, which does not equal zero but
                            is supported for consistency) for the current
                            pixel. (Pixels are drawn successively from
                            the style as the line is drawn, returning to
                            the beginning when the available pixels in
                            the style are exhausted.) Note that this
                            differs from the behavior of gdStyled, in
                            which the values in the style are used as
                            actual pixel colors, except for
                            gdTransparent.
                            
                    gdDashSize _(CONSTANT)_
                            The length of a dash in a dashed line.
                            Defined to be 4 for backwards compatibility
                            with programs that use gdImageDashedLine. New
                            programs should use gdImageSetStyle and call
                            the standard gdImageLine function with the
                            special "color" gdStyled or gdStyledBrushed.
                            
                    gdTiled _(CONSTANT)_
                            Used in place of a normal color in
                            gdImageFilledRectangle, gdImageFilledPolygon,
                            gdImageFill, and gdImageFillToBorder. gdTiled
                            selects a pixel from the tile image set with
                            gdImageSetTile in such a way as to ensure
                            that the filled area will be tiled with
                            copies of the tile image. See the discussions
                            of gdImageFill and gdImageFillToBorder for
                            special restrictions regarding those
                            functions.
                            
                    gdTransparent _(CONSTANT)_
                            Used in place of a normal color in a style to
                            be set with gdImageSetStyle. gdTransparent is
                            _not_ the transparent color index of the
                            image; for that functionality please see
                            gdImageColorTransparent.
                            
  About the additional .gd image file format
  
                            In addition to reading and writing the PNG
                            format and reading the X Bitmap format, gd
                            has the capability to read and write its own
                            ".gd" format. This format is _not_ intended
                            for general purpose use and should never be
                            used to distribute images. It is not a
                            compressed format. Its purpose is solely to
                            allow very fast loading of images your
                            program needs often in order to build other
                            images for output. If you are experiencing
                            performance problems when loading large,
                            fixed PNG images your program needs to
                            produce its output images, you may wish to
                            examine the functions gdImageCreateFromGd and
                            gdImageGd, which read and write .gd format
                            images.
                            
                            The program "pngtogd.c" is provided as a
                            simple way of converting .png files to .gd
                            format. I emphasize again that you will not
                            need to use this format unless you have a
                            need for high-speed loading of a few
                            frequently-used images in your program.
                            
  About the .gd2 image file format
  
                            In addition to reading and writing the PNG
                            format and reading the X Bitmap format, gd
                            has the capability to read and write its own
                            ".gd2" format. This format is _not_ intended
                            for general purpose use and should never be
                            used to distribute images. It is a compressed
                            format allowing pseudo-random access to large
                            image files. Its purpose is solely to allow
                            very fast loading of _parts_ of images If you
                            are experiencing performance problems when
                            loading large, fixed PNG images your program
                            needs to produce its output images, you may
                            wish to examine the functions
                            gdImageCreateFromGd2,
                            gdImageCreateFromGd2Part and gdImageGd2,
                            which read and write .gd2 format images.
                            
                            The program "pngtogd2.c" is provided as a
                            simple way of converting .png files to .gd2
                            format.
                            
  About the gdIOCtx structure
  
                            Version 1.5 of GD added a new style of I/O
                            based on an IOCtx structure (the most
                            up-to-date version can be found in gd_io.h):
                            

typedef struct gdIOCtx {
        int     (*getC)(struct gdIOCtx*);
        int     (*getBuf)(struct gdIOCtx*, void*, int);

        void     (*putC)(struct gdIOCtx*, int);
        int     (*putBuf)(struct gdIOCtx*, const void*, int);

        int     (*seek)(struct gdIOCtx*, const int);
        long    (*tell)(struct gdIOCtx*);

        void    (*free)(struct gdIOCtx*);

} gdIOCtx;

                    Most functions that accepted files in previous
                            versions now also have a counterpart that
                            accepts an I/O context. These functions have
                            a 'Ctx' suffix.
                            
                            The Ctx routines use the function pointers in
                            the I/O context pointed to by gdIOCtx to
                            perform all I/O. Examples of how to implement
                            an I/O context can be found in io_file.c
                            (which provides a wrapper for file routines),
                            and io_dp.c (which implements in-memory
                            storage).
                            
                            It is not necessary to implement all
                            functions in an I/O context if you know that
                            it will only be used in limited
                            cirsumstances. At the time of writing
                            (Version 1.6.1, July 1999), the known
                            requirements are:
                            
                            All   Must have 'free',
                            Anything that reads from the context Must
                            have 'getC' and 'getBuf',
                            Anything that writes to the context Must have
                            'putC' and 'putBuf'.
                            If gdCreateFromGd2Part is called Must also
                            have 'seek' and 'tell'.
                            If gdImageGd2 is called Must also have 'seek'
                            and 'tell'.
                            
  Please tell us you're using gd!
  
                            When you contact us and let us know you are
                            using gd, you help us justify the time spent
                            in maintaining and improving it. So please
                            let us know. If the results are publicly
                            visible on the web, a URL is a wonderful
                            thing to receive, but if it's not a publicly
                            visible project, a simple note is just as
                            welcome.
                            
  If you have problems
  
                            If you have any difficulties with gd, feel
                            free to contact the author, Thomas Boutell.
                            Problems relating to the gd2 format should be
                            addressed to Philip Warner.
                            
                            _Be sure to read this manual carefully first.
                            _
  Alphabetical quick index
  
                            gdBrushed | gdDashSize | gdFont | gdFontPtr |
                            gdImage | gdImageArc | gdImageBlue |
                            gdImageBoundsSafe | gdImageChar |
                            gdImageCharUp | gdImageColorAllocate |
                            gdImageColorClosest | gdImageColorDeallocate
                            | gdImageColorExact | gdImageColorResolve |
                            gdImageColorTransparent | gdImageCopy |
                            gdImageCopyResized | gdImageCreate |
                            gdImageCreateFromGd | gdImageCreateFromGd2 |
                            gdImageCreateFromGd2Part |
                            gdImageCreateFromPng |
                            gdImageCreateFromPngSource |
                            gdImageCreateFromXbm | gdImageCreateFromXpm |
                            gdImageDashedLine | gdImageDestroy |
                            gdImageFill | gdImageFillToBorder |
                            gdImageFilledRectangle | gdImageGd |
                            gdImageGd2 | gdImageGetInterlaced |
                            gdImageGetPixel | gdImageGetTransparent |
                            gdImageGreen | gdImageInterlace | gdImageLine
                            | gdImageFilledPolygon | gdImagePaletteCopy |
                            gdImagePng | gdImagePngToSink |
                            gdImagePolygon | gdImagePtr |
                            gdImageRectangle | gdImageRed |
                            gdImageSetBrush | gdImageSetPixel |
                            gdImageSetStyle | gdImageSetTile |
                            gdImageString | gdImageString16 |
                            gdImageStringTTF | gdImageStringUp |
                            gdImageStringUp16 | gdMaxColors | gdPoint |
                            gdStyled | gdStyledBrushed | gdTiled |
                            gdTransparent
                            
                            _Boutell.Com, Inc._
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