gd 1.2

A graphics library for fast GIF creation

Follow this link to the latest version of this document.

Table of Contents

• Credits and license terms
• What's new in version 1.2?
• What's new in version 1.1.1?
• What is gd?
• What if I want to use Perl instead of C?
• What if I want to use Tcl instead of C?
• What if I want to use another scripting 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
• webgif: 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
• Using gd from tcl
• Alphabetical quick index

Up to the Quest Home Page

Credits and license terms

gd 1.2 is copyright 1994, 1995, Quest Protein Database Center, Cold Spring Harbor Labs. Permission granted to copy and distribute this work provided that this notice remains intact. Credit for the library must be given to the Quest Protein Database Center, Cold Spring Harbor Labs, in all derived works. This does not affect your ownership of the derived work itself, and the intent is to assure proper credit for Quest, not to interfere with your use of gd. If you have questions, ask. ("Derived works" includes all programs that utilize the library. Credit must be given in user-visible documentation.)

If you wish to release modifications to gd, please clear them first by sending email to boutell@boutell.com; if this is not done, any modified version of the gd library must be clearly labeled as such.

The Quest Protein Database Center is funded under Grant P41-RR02188 by the National Institutes of Health.

Written by Thomas Boutell, 2/94 - 7/95.

The GIF compression code is based on that found in the pbmplus utilities, which in turn is based on GIFENCOD by David Rowley. See the notice below:

/*
** Based on GIFENCOD by David Rowley .A
** Lempel-Zim compression based on "compress".
**
** Modified by Marcel Wijkstra 
**
** Copyright (C) 1989 by Jef Poskanzer.
**
** Permission to use, copy, modify, and distribute this software and its
** documentation for any purpose and without fee is hereby granted, provided
** that the above copyright notice appear in all copies and that both that
** copyright notice and this permission notice appear in supporting
** documentation.  This software is provided "as is" without express or
** implied warranty.
**
** The Graphics Interchange Format(c) is the Copyright property of
** CompuServe Incorporated.  GIF(sm) is a Service Mark property of
** CompuServe Incorporated.
*/

The GIF decompression is based on that found in the pbmplus utilities, which in turn is based on GIFDECOD by David Koblas. See the notice below:

/* +-------------------------------------------------------------------+ */
/* | Copyright 1990, 1991, 1993, David Koblas.  (koblas@netcom.com)    | */
/* |   Permission to use, copy, modify, and distribute this software   | */
/* |   and its documentation for any purpose and without fee is hereby | */
/* |   granted, provided that the above copyright notice appear in all | */
/* |   copies and that both that copyright notice and this permission  | */
/* |   notice appear in supporting documentation.  This software is    | */
/* |   provided "as is" without express or implied warranty.           | */
/* +-------------------------------------------------------------------+ */

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 .GIF file. This is particularly useful in World Wide Web applications, where .GIF is the format used for inline images.

gd is not a paint program. If you are looking for a paint program, try xpaint by David Koblas, available by anonymous FTP from ftp.netcom.com in pub/ko/koblas. (That package is for the X Window System; for the Mac and the PC, paint programs are considerably easier to find.)

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 1.2 incorporates most of the commonly requested features for a 2D package. Font support does need improvement, and support for the PNG graphics format will arrive in a forthcoming release.

What if I want to use Perl instead of C?

These packages are based on gd 1.1.1 as of this writing but should be compatible with gd 1.2 with minimal tweaking.

• gdit, by David Harvey-George
• tgd, by Bradley K. Sherman
• fly, by Martin Gleeson

What's new in version 1.2?

Version 1.2 moves gd to ANSI standard C. Non-ANSI C compilers, such as the old SunOS 4.1.3 cc compiler, will not work. The use of pre-ANSI C led to several long-standing bugs, and the ANSI C standard has been with us for nearly ten years now. If your compiler does not support ANSI, upgrade to a recent release of your compiler, or get gcc, which is free and does support ANSI C.

The provided Unix Makefile has been changed to be a bit more broadly compatible, and to acknowledge the changes that may be necessary on various systems.

Version 1.2 also includes the following improvements:

• gdImageCopy and gdImageCopyResized now ignore pixels which are transparent in the source image. This is allows easy copying of non-square regions, which could previously be accomplished only with brushes.
• gdImageFilledPolygon now draws horizontal edges correctly, correcting a long-standing bug. In addition, gdImageFilledPolygon copes with polygons which have several horizontal segments on the same scan line. There can still be a few pixels of disagreement between gdImagePolygon and gdImageFilledPolygon with regard to the borders of the polygon, however.
• Several new public-domain fonts are included, courtesy of Joseph M. Orost at AT&T.
• gd now properly recognizes an existing image with a high color slot number transparent.
• Bugs in the gdImageCreateFromXbm function have been corrected. Previously the function was incorrect for image widths not evenly divisible by eight.

What's new in version 1.1.1?

gdImageSetStyle now copies the style array to make it easier to take advantage of the line styling feature; it is now safe to free the memory associated with your style array after setting a style (or allocate styles on the stack...). This should not break existing code.

webgif, a small but powerful GIF-manipulating utility program, has been added as an additional code example.

An access macro to determine whether an image is interlaced has been added; see gdImageGetInterlaced.

A better Unix Makefile, provided by Mark Scott. Note that an actual library (libgd.a) is now produced; you will want to link with this library in your own gd apps, in the same manner that gddemo and giftogd link with it. You no longer need to explicitly list the standard font files on the link line. No doubt many users have already made this enhancement themselves.

Important: depending on your system you may need to rewrite this Makefile. Basic code-compiling skills are expected for the use of this library.

David Koblas has been given proper credit for the original GIF decoding routine; previously I erroneously credited David Rowley with both the encoder and the decoder.

gdImageFill no longer crashes when attempting to fill a region with the color it already has. Also, attempting to fill a region with the special color gdTiled no longer crashes.

However, filling a region with a transparent tile has been forbidden (gdImageFill simply draws nothing in this case). Otherwise, gd would not know when to stop drawing without the use of an additional image to keep track of which pixels have been visited.

Invoking gdImageFillToBorder with a special border color such as gdTiled now fails, for similar reasons. However, the color you are filling with can be gdTiled, even if it is transparent. See the discussion of gdImageFillToBorder for additional caveats.

Many documentation fixes.

What's new in version 1.1?

• Polygon fills
• Line styling
• "Brushing" of lines with a brush image
• Tiling of polygon, rectangle and flood-fills
• Interlaced GIFs for gradual fade-in
• Macros to access image size, etc.

What else do I need to use gd?

To use gd, you will need an ANSI C compiler. Any full-ANSI-standard C compiler should be adequate, although those with PCs will need to replace the Makefile with one of their own. The cc compiler released with SunOS 4.1.3 is not an ANSI C compiler. Get gcc, which is freely available. See the Sun-related newsgroups for more information.

You will also want a GIF 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. lview is a good package for Windows PCs; xv is a good package for X11. There are GIF viewers available for every graphics-capable computer out there, so consult newsgroups relevant to your particular system.

How do I get gd?

You can fetch gd as a compressed tar file, Or you can FTP it directly from isis.cshl.org, in the subdirectory pub/gd.

How do I build gd?

In order to build gd, first uncompress and untar the gd.tar file with the following commands:

Note: if you have a non-Unix system, you will need to acquire versions of "uncompress" and "tar" suitable for your system. Both have been ported to PC and Mac environments. Consult newsgroups relevant to your particular system.

uncompress gd1.2.tar.Z
tar -xf gd1.2.tar

cd to this directory and examine the Makefile, which you may need to change slightly depending on your installation (or more than slightly for a Windows or Mac environment).

Now, to build the demonstration program, just type "make gddemo" if you are working in a command-line environment. If all goes well, the program "gddemo" will be compiled and linked without incident. Depending on your system you may need to edit the Makefile. Understanding the basic techniques of compiling and linking programs on your system is up to you.

You have now built 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.gif. (Note there is also a file named demoin.gif, which is provided in the package as part of the demonstration.)

Display demoout.gif in your GIF viewer. The image should be 128x128 pixels and should contain an image of the space shuttle with the word "hi" written in the upper left corner twice (once across and once upwards), an arc in the middle and an oval intersecting the arc (these are somewhat faint).

In addition, a diagonal line made up of tiny space shuttle images should appear from the lower left to the upper right corner. A blue frame with green interior trim should surround the picture.

(If you are missing the demoin.gif file, the other items should appear anyway.)

Look at demoin.gif to see the original space shuttle image which was scaled and copied into the output image.

gd basics: using gd in your program

If you want to use the provided fonts, include gdfontt.h, gdfonts.h, gdfontmb.h, gdfontl.h and/or gdfontg.h. 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 GIF 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.gif", "wb");

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

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

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

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.

Webgif: a more powerful gd example

webgif.c is provided in the distribution. Unix users can simply type "make webgif" to compile the program. Type "webgif" with no arguments to see the available options. A discussion of the code follows.

/* Bring in the gd library functions */
#include "gd.h"

/* Bring in standard I/O and string manipulation functions */
#include 
#include 

int main(argc, argv) 
	int argc;
	char *argv[];
{
	FILE *in;
	FILE *out;
	/* Declare our image pointer */
	gdImagePtr im = 0;
	int i;
       /* We'll clear 'no' once we know the user has made a
		reasonable request. */
	int no = 1;
	/* We'll set 'write' once we know the user's request
		requires that the image be written back to disk. */
	int write = 0;
	/* C programs always get at least one argument; we want at
		least one more (the image), more in practice. */
	if (argc < 2) {
		no = 1;	
		goto usage;
	}
	/* The last argument should be the image. Open the file. */
	in = fopen(argv[argc-1], "rb");	
	if (!in) {
		fprintf(stderr,
			"Error: can't open file %s.\n", argv[argc-1]);
	}
	/* Now load the image. */	
	im = gdImageCreateFromGif(in);
	fclose(in);
	/* If the load failed, it must not be a GIF file. */
	if (!im) {
		fprintf(stderr,
			"Error: %s is not a valid gif file.\n", argv[1]);
		exit(1);	
	}
	/* Consider each argument in turn. */
	for (i=1; (i < (argc-1)); i++) {
		/* -i turns on and off interlacing. */
		if (!strcmp(argv[i], "-i")) {
			if (i == (argc-2)) {
				fprintf(stderr, 
				"Error: -i specified without y or n.\n");
				no = 1;
				goto usage;
			}
			if (!strcmp(argv[i+1], "y")) {
				/* Set interlace. */
				gdImageInterlace(im, 1);
			} else if (!strcmp(argv[i+1], "n")) {
				/* Clear interlace. */
				gdImageInterlace(im, 0);
			} else {
				fprintf(stderr,
				"Error: -i specified without y or n.\n");
				no = 1;
				goto usage;
			}
			i++;
			no = 0;
			write = 1;
		} else if (!strcmp(argv[i], "-t")) {
			/* Set transparent index (or none). */
			int index;
			if (i == (argc-2)) {
				fprintf(stderr,
		"Error: -t specified without a color table index.\n");
				no = 1;
				goto usage;
			}
			if (!strcmp(argv[i+1], "none")) {
				/* -1 means not transparent. */
				gdImageColorTransparent(im, -1);
			} else {
				/* OK, get an integer and set the index. */
				index = atoi(argv[i+1]);
				gdImageColorTransparent(im, index);
			}
			i++;
			write = 1;
			no = 0;
		} else if (!strcmp(argv[i], "-l")) {
			/* List the colors in the color table. */
			int j;
			/* Tabs used below. */
			printf("Index	Red	Green	Blue\n");
			for (j=0; (j < gdImageColorsTotal(im)); j++) {
				/* Use access macros to learn colors. */
				printf("%d	%d	%d	%d\n",
					j, 
					gdImageRed(im, j),
					gdImageGreen(im, j),
					gdImageBlue(im, j));
			}
			no = 0;
		} else if (!strcmp(argv[i], "-d")) {
			/* Output dimensions, etc. */
			int t;
			printf("Width: %d Height: %d Colors: %d\n",
				gdImageSX(im), gdImageSY(im),
				gdImageColorsTotal(im));
			t = gdImageGetTransparent(im);
			if (t != (-1)) {
				printf("Transparent index: %d\n", t);
			} else {
				/* -1 means the image is not transparent. */
				printf("Transparent index: none\n");
			}
			if (gdImageGetInterlaced(im)) {
				printf("Interlaced: yes\n");	
			} else {
				printf("Interlaced: no\n");	
			}
			no = 0;
		} else {
			fprintf(stderr, "Unknown argument: %s\n", argv[i]);
			break;	
		}
	}
usage:
	if (no) {
		/* If the command failed, output an explanation. */
		fprintf(stderr, 
	"Usage: webgif [-i y|n ] [-l] [-t index|off ] [-d] gifname.gif\n");
		fprintf(stderr, 
	"Where -i controls interlace (specify y or n for yes or no),\n");
		fprintf(stderr, 
	"-l outputs a table of color indexes, -t sets the specified\n");
		fprintf(stderr, 
	"color index (0-255 or none) to be the transparent color, and\n");
		fprintf(stderr,
	"-d reports the dimensions and other characteristics of the image.\n");
		fprintf(stderr, 
	"Note: you may wish to pipe to \"more\" when using the -l option.\n");
	} 
	if (write) {
		/* Open a temporary file. */
		out = fopen("temp.tmp", "wb");
		if (!out) {
			fprintf(stderr,
				"Unable to write to temp.tmp -- exiting\n");
			exit(1);
		}
		/* Write the new gif. */
		gdImageGif(im, out);
		fclose(out);
		/* Erase the old gif. */
		unlink(argv[argc-1]);
		/* Rename the new to the old. */
		rename("temp.tmp", argv[argc-1]);
	}
	/* Delete the image from memory. */
	if (im) {
		gdImageDestroy(im);
	}
	/* All's well that ends well. */
	return 0;
}

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.

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);

gdImageCreateFromGif(FILE *in) (FUNCTION)

gdImageCreateFromGif is called to load images from GIF format files. Invoke gdImageCreateFromGif with an already opened pointer to a file containing the desired image. gdImageCreateFromGif 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 GIF image). gdImageCreateFromGif 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("mygif.gif", "rb");
im = gdImageCreateFromGif(in);
fclose(in);
/* ... Use the image ... */
gdImageDestroy(im);

gdImageCreateFromGd(FILE *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 GIF.) 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);

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);

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 gdImageGif(gdImagePtr im, FILE *out) (FUNCTION)

gdImageGif outputs the specified image to the specified file in GIF format. The file must be open for writing. Under MSDOS, 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. gdImageGif 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.gif", "wb");
/* Write GIF */
gdImageGif(im, out);
/* Close file */
fclose(out);
/* Destroy image */
gdImageDestroy(im);

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, 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. gdImageGif 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);

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 environments. (Of course, in a Unix or 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 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 GIFs 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 GIF. 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.gif", "rb");
brush = gdImageCreateFromGif(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 GIFs 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 GIF. 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.gif", "rb");
tile = gdImageCreateFromGif(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("mygif.gif", "rb");
im = gdImageCreateFromGif(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.) 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.) 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, 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.) 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 gdImageStringUp(gdImagePtr im, gdFontPtr font, int x, int y, 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);

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 GIF 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.

... 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 GIF 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.gif is a scanned photograph with
	many colors. */
in = fopen("photo.gif", "rb");
im = gdImageCreateFromGif(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.gif", "rb");
im = gdImageCreateFromGif(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 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.gif", "rb");
im = gdImageCreateFromGif(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.gif", "rb");
im = gdImageCreateFromGif(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.gif", "wb");
gdImageGif(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 gif to tile the larger one with */
in = fopen("small.gif", "rb");
im_in = gdImageCreateFromGif(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.gif", "wb");
gdImageGif(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 gif to expand in the larger one */
in = fopen("small.gif", "rb");
im_in = gdImageCreateFromGif(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.gif", "wb");
gdImageGif(im_out, out);
fclose(out);
gdImageDestroy(im_in);
gdImageDestroy(im_out);

Miscellaneous Functions

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 GIF format; the gd and xbm formats do not support interlace.

When a GIF is loaded with gdImageCreateFromGif , interlace will be set according to the setting in the GIF file.

Note that many GIF viewers and web browsers do not support interlace. However, the interlaced GIF 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.gif", "wb");
/* And save the image */
gdImageGif(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 GIF file according to the GIF 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.

The program "giftogd.c" is provided as a simple way of converting .gif 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.

Please tell us you're using gd!

Alphabetical quick index

Thomas Boutell, boutell@netcom.com