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

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

Image creation, destruction, loading and saving

gdImageCreate(sx, sy) (FUNCTION)

gdImageCreate is called to create palette-based images, with no more than 256 colors. 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);

gdImageCreateTrueColor(sx, sy) (FUNCTION)

gdImageCreateTrueColor is called to create truecolor images, with an essentially unlimited number of colors. Invoke gdImageCreateTrueColor with the x and y dimensions of the desired image. gdImageCreateTrueColor returns a gdImagePtr to the new image, or NULL if unable to allocate the image. The image must eventually be destroyed using gdImageDestroy().

Truecolor images are always filled with black at creation time. There is no concept of a "background" color index.

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

gdImageCreateFromJpeg(FILE *in) (FUNCTION)
gdImageCreateFromJpegPtr(int size, void *data) (FUNCTION)
gdImageCreateFromJpegCtx(gdIOCtx *in) (FUNCTION)

gdImageCreateFromJpeg is called to load truecolor images from JPEG format files. Invoke gdImageCreateFromJpeg with an already opened pointer to a file containing the desired image. gdImageCreateFromJpeg returns a gdImagePtr to the new truecolor image, or NULL if unable to load the image (most often because the file is corrupt or does not contain a JPEG image). gdImageCreateFromJpeg 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(). The returned image is always a truecolor image.

If you already have the image file in memory, pass the size of the file and a pointer to the file's data to gdImageCreateFromJpegPtr, which is otherwise identical to gdImageCreateFromJpeg.

gdImagePtr im;
... inside a function ...
FILE *in;
in = fopen("myjpeg.jpg", "rb");
im = gdImageCreateFromJpeg(in);
fclose(in);
/* ... Use the image ... */
gdImageDestroy(im);

gdImageCreateFromPng(FILE *in) (FUNCTION)
gdImageCreateFromPngPtr(int size, void *data) (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().

If you already have the image file in memory, pass the size of the file and a pointer to the file's data to gdImageCreateFromPngPtr, which is otherwise identical to gdImageCreateFromPng.

If the PNG image being loaded is a truecolor image, the resulting gdImagePtr will refer to a truecolor image. If the PNG image being loaded is a palette or grayscale image, the resulting gdImagePtr will refer to a palette image. gd retains only 8 bits of resolution for each of the red, green and blue channels, and only 7 bits of resolution for the alpha channel. The former restriction affects only a handful of very rare 48-bit color and 16-bit grayscale PNG images. The second restriction affects all semitransparent PNG images, but the difference is essentially invisible to the eye. 7 bits of alpha channel resolution is, in practice, quite a lot.

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)

Deprecated in favor of gdImageCreateFromPngCtx. Should not be used in new applications.

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;
}

gdImageCreateFromGif(FILE *in) (FUNCTION)
gdImageCreateFromGifPtr(int size, void *data) (FUNCTION)
gdImageCreateFromGifCtx(gdIOCtx *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().

If you already have the image file in memory, pass the size of the file and a pointer to the file's data to gdImageCreateFromGifPtr, which is otherwise identical to gdImageCreateFromGif.

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)

gdImageCreateFromGdPtr(int size, void *data) (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 or JPEG.)

If you already have the image file in memory, pass the size of the file and a pointer to the file's data to gdImageCreateFromGdPtr, which is otherwise identical to gdImageCreateFromGd.

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)
gdImageCreateFromGd2Ptr(int size, void *data) (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 as maximum compression of the entire image would be.)

If you already have the image file in memory, pass the size of the file and a pointer to the file's data to gdImageCreateFromGd2Ptr, which is otherwise identical to gdImageCreateFromGd2.

gdImageCreateFromGd2 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)
gdImageCreateFromGd2PartPtr(int size, void *data, 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().

If you already have the image file in memory, you may use gdImageCreateFromGd2PartPtr. Pass the size of the image file, in bytes, as the first argument and the pointer to the image file data as the second argument.

gdImageCreateFromWBMP(FILE *in) (FUNCTION)
gdImageCreateFromWBMPPtr(int size, void *data) (FUNCTION)
gdImageCreateFromWBMPCtx(gdIOCtx *in) (FUNCTION)

gdImageCreateFromWBMP is called to load images from WBMP format files. Invoke gdImageCreateFromWBMP with an already opened pointer to a file containing the desired image. gdImageCreateFromWBMP 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). gdImageCreateFromWBMP 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().

If you already have the image file in memory, pass the size of the file and a pointer to the file's data to gdImageCreateFromWBMPPtr, which is otherwise identical to gdImageCreateFromWBMP.

gdImagePtr im;
... inside a function ...
FILE *in;
in = fopen("mywbmp.wbmp", "rb");
im = gdImageCreateFromWBMP(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);

gdImageCreateFromXpm(char *filename) (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. Unlike most gd file functions, the Xpm functions require filenames, not file pointers. 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). 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 gdImageJpeg(gdImagePtr im, FILE *out, int quality) (FUNCTION)
void gdImageJpegCtx(gdImagePtr im, gdIOCtx *out, int quality) (FUNCTION)

gdImageJpeg outputs the specified image to the specified file in JPEG 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. gdImageJpeg does not close the file; your code must do so.

If quality is negative, the default IJG JPEG quality value (which should yield a good general quality / size tradeoff for most situations) is used. Otherwise, for practical purposes, quality should be a value in the range 0-95, higher quality values usually implying both higher quality and larger image sizes.

If you have set image interlacing using gdImageInterlace, this function will interpret that to mean you wish to output a progressive JPEG. Some programs (e.g., Web browsers) can display progressive JPEGs incrementally; this can be useful when browsing over a relatively slow communications link, for example. Progressive JPEGs can also be slightly smaller than sequential (non-progressive) JPEGs.

... 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.jpg", "wb");
/* Write JPEG using default quality */
gdImageJpeg(im, out, -1);
/* Close file */
fclose(out);
/* Destroy image */
gdImageDestroy(im);

void* gdImageJpegPtr(gdImagePtr im, int *size, int quality) (FUNCTION)

Identical to gdImageJpeg except that it returns a pointer to a memory area with the JPEG data. This memory must be freed by the caller when it is no longer needed. The caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.

void gdImageGif(gdImagePtr im, FILE *out)
void gdImageGifCtx(gdImagePtr im, gdIOCtx *out) (FUNCTION)

gdImageGif 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. gdImageGif does not close the file; your code must do so.

GIF does not support true color; GIF images can contain a maximum of 256 colors. If the image to be written is a truecolor image, such as those created with gdImageCreateTrueColor or loaded from a JPEG or a truecolor PNG image file, a palette-based temporary image will automatically be created internally using the gdImageCreatePaletteFromTrueColor function. The original image pixels are not modified. This conversion produces high quality palettes but does require some CPU time. If you are regularly converting truecolor to palette in this way, you should consider creating your image as a palette-based image in the first place.

... 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* gdImageGifPtr(gdImagePtr im, int *size) (FUNCTION)

Identical to gdImageGif except that it returns a pointer to a memory area with the GIF data. This memory must be freed by the caller when it is no longer needed. The caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.

void gdImagePng(gdImagePtr im, FILE *out)
void gdImagePngCtx(gdImagePtr im, gdIOCtx *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 gdImagePngEx(gdImagePtr im, FILE *out, int level)
void gdImagePngCtxEx(gdImagePtr im, gdIOCtx *out, int level) (FUNCTION)

Like gdImagePng, gdImagePngEx outputs the specified image to the specified file in PNG format. In addition, gdImagePngEx allows the level of compression to be specified. A compression level of 0 means "no compression." A compression level of 1 means "compressed, but as quickly as possible." A compression level of 9 means "compressed as much as possible to produce the smallest possible file." A compression level of -1 will use the default compression level at the time zlib was compiled on your system.

For more information, see gdImagePng.

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 caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.

void* gdImagePngPtrEx(gdImagePtr im, int *size, int level) (FUNCTION)

Like gdImagePngPtr, gdImagePngPtrEx returns a pointer to a PNG image in allocated memory. In addition, gdImagePngPtrEx allows the level of compression to be specified. A compression level of 0 means "no compression." A compression level of 1 means "compressed, but as quickly as possible." A compression level of 9 means "compressed as much as possible to produce the smallest possible file." A compression level of -1 will use the default compression level at the time zlib was compiled on your system.

For more information, see gdImagePngPtr.

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 gdImageWBMP(gdImagePtr im, int fg, FILE *out)
gdImageWBMPCtx(gdIOCtx *out) (FUNCTION)(FUNCTION)

gdImageWBMP outputs the specified image to the specified file in WBMP 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. gdImageWBMP does not close the file; your code must do so.

WBMP file support is black and white only. The color index specified by the fg argument is the "foreground," and only pixels of this color will be set in the WBMP file. All other pixels will be considered "background."

... 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.wbmp", "wb");
/* Write WBMP, with black as foreground */
gdImageWBMP(im, black, out);
/* Close file */
fclose(out);
/* Destroy image */
gdImageDestroy(im);

void* gdImageWBMPPtr(gdImagePtr im, int *size) (FUNCTION)

Identical to gdImageWBMP except that it returns a pointer to a memory area with the WBMP data. This memory must be freed by the caller when it is no longer needed. The caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.

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 caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.

void gdImageGd2(gdImagePtr im, FILE *out, int chunkSize, int fmt)
void gdImageGd2Ctx(gdImagePtr im, gdIOCtx *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 caller must invoke gdFree(), not free(), unless the caller is absolutely certain that the same implementations of malloc, free, etc. are used both at library build time and at application build time. The 'size' parameter receives the total size of the block of memory.

void gdImageTrueColorToPalette(gdImagePtr im, int ditherFlag, int colorsWanted)
gdImagePtr gdImageCreatePaletteFromTrueColor(gdImagePtr im, int ditherFlag, int colorsWanted) (FUNCTION)

gdImageCreatePaletteFromTrueColor returns a new image. gdImageTrueColorToPalette permanently converts the existing image. The two functions are otherwise identical.

The function converts a truecolor image to a palette-based image, using a high-quality two-pass quantization routine. If ditherFlag is set, the image will be dithered to approximate colors better, at the expense of some obvious "speckling." colorsWanted can be anything up to 256. If the original source image includes photographic information or anything that came out of a JPEG, 256 is strongly recommended. 100% transparency of a single transparent color in the original truecolor image will be preserved. There is no other support for preservation of alpha channel or transparency in the destination image.

For best results, don't use this function -- write real truecolor PNGs and JPEGs. The disk space gain of conversion to palette is not great (for small images it can be negative) and the quality loss is ugly. However, the version of this function included in version 2.0.12 and later does do a better job than the version included prior to 2.0.12.

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 gdImageFilledArc(gdImagePtr im, int cx, int cy, int w, int h, int s, int e, int color, int style) (FUNCTION)

gdImageFilledArc 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 filled in the color specified by the second to 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. The last argument is a bitwise OR of the following possibilities:

• gdArc
• gdChord
• gdPie (synonym for gdChord)
• gdNoFill
• gdEdged

gdArc and gdChord are mutually exclusive; gdChord just connects the starting and ending angles with a straight line, while gdArc produces a rounded edge. gdPie is a synonym for gdArc. gdNoFill indicates that the arc or chord should be outlined, not filled. gdEdged, used together with gdNoFill, indicates that the beginning and ending angles should be connected to the center; this is a good way to outline (rather than fill) a 'pie slice'.

... 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 a filled pie slice in the image. */
gdImageFilledArc(im, 50, 25, 98, 48, 0, 45, white, gdArc);
/* ... Do something with the image, such as 
  saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

void gdImageFilledEllipse(gdImagePtr im, int cx, int cy, int w, int h, int color) (FUNCTION)

gdImageFilledEllipse is used to draw an ellipse centered at the given point, with the specified width and height in pixels. The ellipse is filled in the color specified by the last argument.

... 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 a filled ellipse in the image. */
gdImageFilledEllipse(im, 50, 25, 98, 48, 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 gdImageSetAntiAliased(gdImagePtr im, int c) (FUNCTION)

"Antialiasing" is a process by which jagged edges associated with line drawing can be reduced by blending the foreground color with an appropriate percentage of the background, depending on how much of the pixel in question is actually within the boundaries of the line being drawn. All line-drawing functions, such as gdImageLine and gdImagePolygon, will draw antialiased lines if the special "color" gdAntiAliased is used when calling them.

gdImageSetAntiAliased is used to specify the actual foreground color to be used when drawing antialiased lines. You may set any color to be the foreground, however as of version 2.0.12 an alpha channel component is not supported.

Antialiased lines can be drawn on both truecolor and palette-based images. However, attempts to draw antialiased lines on highly complex palette-based backgrounds may not give satisfactory results, due to the limited number of colors available in the palette. Antialiased line-drawing on simple backgrounds should work well with palette-based images; otherwise create or fetch a truecolor image instead.

You need not take any special action when you are finished with antialised line drawing.

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

See also gdAntiAliased and gdSetAntiAliasedDontBlend.

void gdImageSetAntiAliasedDontBlend(gdImagePtr im, int c) (FUNCTION)

Normally, when drawing lines with the special gdAntiAliased "color," blending with the background to reduce jagged edges is the desired behavior. However, when it is desired that lines not be blended with one particular color when it is encountered in the background, the gdImageSetAntiAliasedDontBlend function can be used to indicate the special color that the foreground should stand out more clearly against.

... inside a function ...
gdImagePtr im, brush;
int black;
int blue;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);  
blue = gdImageColorAllocate(im, 0, 0, 255);
white = gdImageColorAllocate(im, 255, 255, 255);

gdImageSetAntiAliased(im, blue);
/* The portion of the line that crosses this white rectangle will
  not be blended smoothly */
gdImageSetAntiAliasedDontBlend(im, white);
gdImageFilledRectangle(im, 25, 25, 75, 75, white);
/* Draw a smooth line from the upper left corner 
  to the lower right corner. */
gdImageLine(im, 0, 0, 99, 99, gdAntiAliased);
/* ... Do something with the image, such as 
  saving it to a file... */
/* Destroy it */
gdImageDestroy(im);

See also gdAntiAliased and gdSetAntiAliased.

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);

void gdImageSetThickness(gdImagePtr im, int thickness) (FUNCTION)

gdImageSetThickness determines the width of lines drawn by the gdImageLine, gdImagePolygon and related functions, in pixels.

... 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 thickness. */
gdImageSetThickness(im, 4);
/* Draw a fat 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 gdImageAlphaBlending(gdImagePtr im, int blending) (FUNCTION)

The gdImageAlphaBlending function allows for two different modes of drawing on truecolor images. In blending mode, which is on by default (gd 2.0.2 and above), the alpha channel component of the color supplied to all drawing functions, such as gdImageSetPixel, determines how much of the underlying color should be allowed to shine through. As a result, gd automatically blends the existing color at that point with the drawing color, and stores the result in the image. The resulting pixel is opaque. In non-blending mode, the drawing color is copied literally with its alpha channel information, replacing the destination pixel. Blending mode is not available when drawing on palette images.

gdImagePtr im;
int red, blue;
im = gdImageCreateTrueColor(100, 100);
/* Background color */
red = gdTrueColor(255, 0, 0);  
gdImageFilledRectangle(im, 0, 0, 100, 100, red);
/* Drawing color. Full transparency would be an alpha channel value
  of 127 (gd has a 7 bit alpha chnanel). 0 is opaque,
  127 is transparent. So cut gdAlphaTransparent in half to get
  50% blending. */
blue = gdTrueColorAlpha(0, 0, 255, gdAlphaTransparent / 2);  
/* Draw with blending. Result will be 50% red, 50% blue: yellow 
  (emitted light, remember, not reflected light. What you learned 
  in Kindergarten is wrong here). */
gdImageAlphaBlending(im, 1);
gdImageFilledRectangle(im, 0, 0, 25, 25, blue);
/* Draw without blending. Result will be 50% blue, 50%
  the background color of the image viewer or web browser
  used; results in browsers that don't support
  semi-transparent pixels are unpredictable! */
gdImageAlphaBlending(im, 0);
gdImageFilledRectangle(im, 75, 75, 25, 25, blue);
/* Write the image to disk, etc. */

void gdImageSaveAlpha(gdImagePtr im, int saveFlag) (FUNCTION)

By default, gd 2.0.2 and above do not attempt to save full alpha channel information (as opposed to single-color transparency) when saving PNG images. (PNG is currently the only output format supported by gd which can accommodate alpa channel information.) This saves space in the output file. If you wish to create an image with alpha channel information for use with tools that support it, call gdImageSaveAlpha(im, 1) to turn on saving of such information, and call gdImageAlphaBlending(im, 0) to turn off alpha blending within the library so that alpha channel information is actually stored in the image rather than being composited immediately at the time that drawing functions are invoked.

void gdImageSetClip(gdImagePtr im, int x1, int y1, int x2, int y2) (FUNCTION)

Establishes a clipping rectangle. Once gdImageSetClip has been called, all future drawing operations will remain within the specified clipping area, until a new gdImageSetClip call takes place. For instance, if a clipping rectangle of 25, 25, 75, 75 has been set within a 100x100 image, a diagonal line from 0,0 to 99,99 will appear only between 25,25 and 75,75.

If gdImageSetClip is never called, the clipping area will be the entire image.

The parameters passed to gdImageSetClip are checked against the dimensions of the image and limited to "safe" values.

... 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 the clipping rectangle. */
gdImageSetClip(im, 25, 25, 75, 75);
/* Draw a line from the upper left corner to the lower right corner. 
  Only the part within the clipping rectangle will appear. */
gdImageLine(im, 0, 0, 99, 99, white);
/* ... Do something with the image, such as 
  saving it to a file ... */
/* Destroy it */
gdImageDestroy(im);

See also gdImageGetClip.

void gdImageGetClip(gdImagePtr im, int *x1P, int *y1P, int *x2P, int *y2P) (FUNCTION)

Fetches the boundaries of the current clipping rectangle.

... Inside a function ... 
gdImagePtr im = gdImageCreateTrueColor(100, 100);
int x1, y1, x2, y2;
gdImageSetClip(im, 25, 25, 75, 75);
gdImageGetClip(im, &x1, &y1, &x2, &y2);
printf("%d %d %d %d\n", x1, y1, x2, y2);

The above code would print:

25 25 75 75

See also gdImageSetClip.

Query Functions

int gdImageAlpha(gdImagePtr im, int color) (MACRO)

gdImageAlpha is a macro which returns the alpha channel component of the specified color index. Alpha channel values vary between 0 (gdAlphaOpaque), which does not blend at all with the background, through 127 (gdAlphaTransparent), which allows the background to shine through 100%. Use this macro rather than accessing the structure members directly. 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 current clipping rectangle, false (0) if not. The clipping rectangle is set by gdImageSetClip and defaults to the entire image. 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 using this function or its macro equivalent in gd.c, gdImageBoundsSafeMacro.

... 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

gdFontPtr gdFontGetSmall(void) (FUNCTION)

Returns a font pointer for the "small" gd font. Your code must include the header file gdfonts.h before calling this function. Under Windows, due to the nature of DLLs, the use of this function is strongly recommended rather than attempting to use the gdFontSmall pointer directly. (You may safely assign the result to a local gdFontPtr variable in your own code.)

See gdImageString for more information and examples, or gdImageStringFT for a freetype-based alternative that supports truetype fonts.

gdFontPtr gdFontGetLarge(void) (FUNCTION)

Returns a font pointer for the "large" gd font. Your code must include the header file gdfontl.h before calling this function. Under Windows, due to the nature of DLLs, the use of this function is strongly recommended rather than attempting to use the gdFontLarge pointer directly. (You may safely assign the result to a local gdFontPtr variable in your own code.)

See gdImageString for more information and examples, or gdImageStringFT for a freetype-based alternative that supports truetype fonts.

gdFontPtr gdFontGetMediumBold(void) (FUNCTION)

Returns a font pointer for the "medium bold" gd font. Your code must include the header file gdfontmb.h before calling this function. Under Windows, due to the nature of DLLs, the use of this function is strongly recommended rather than attempting to use the gdFontMediumBold pointer directly. (You may safely assign the result to a local gdFontPtr variable in your own code.)

See gdImageString for more information and examples, or gdImageStringFT for a freetype-based alternative that supports truetype fonts.

gdFontPtr gdFontGetGiant(void) (FUNCTION)

Returns a font pointer for the "giant" gd font. Your code must include the header file gdfontg.h before calling this function. Under Windows, due to the nature of DLLs, the use of this function is strongly recommended rather than attempting to use the gdFontGiant pointer directly. (You may safely assign the result to a local gdFontPtr variable in your own code.)

See gdImageString for more information and examples, or gdImageStringFT for a freetype-based alternative that supports truetype fonts.

gdFontPtr gdFontGetTiny(void) (FUNCTION)

Returns a font pointer for the "tiny" gd font. Your code must include the header file gdfontt.h before calling this function. Under Windows, due to the nature of DLLs, the use of this function is strongly recommended rather than attempting to use the gdFontTiny pointer directly. (You may safely assign the result to a local gdFontPtr variable in your own code.)

See gdImageString for more information and examples, or gdImageStringFT for a freetype-based alternative that supports truetype fonts.

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 gdImageStringFT for a high quality solution.) 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.

Windows DLL users: although you can use these DLL-exported pointers directly, you cannot easily assign them to other pointers. This will cause hard-to-debug problems. To avoid such troubles, you should call the functions gdFontGetTiny(), gdFontGetSmall(), gdFontGetMediumBold(), gdFontGetLarge(), and gdFontGetGiant() in order to obtain pointers to the fonts under Windows.

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, gdFontGetLarge(), 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.

Windows DLL users: although you can use these DLL-exported pointers directly, you cannot easily assign them to other pointers. This will cause hard-to-debug problems. To avoid such troubles, you should call the functions gdFontGetTiny(), gdFontGetSmall(), gdFontGetMediumBold(), gdFontGetLarge(), and gdFontGetGiant() in order to obtain pointers to the fonts under Windows.

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, gdFontGetLarge(),
  0, gdFontGetLarge()->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.

Windows DLL users: although you can use these DLL-exported pointers directly, you cannot easily assign them to other pointers. This will cause hard-to-debug problems. To avoid such troubles, you should call the functions gdFontGetTiny(), gdFontGetSmall(), gdFontGetMediumBold(), gdFontGetLarge(), and gdFontGetGiant() in order to obtain pointers to the fonts under Windows.

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 gdImageStringFT for a high quality solution.) 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, gdFontGetLarge(),
  im->sx / 2 - (strlen(s) * gdFontGetLarge()->w / 2),
  im->sy / 2 - gdFontGetLarge()->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)

gdImageString16 is used to draw multiple 16-bit characters on the image. (To draw single characters, use gdImageChar16.) The second argument is a pointer to a font definition structure; no 16-bit fonts are provided with gd as standard equipment and there does not seem to be much momentum to create them although the bdftogd script can do so. The preferred solution is gdImageStringFT, which uses freetype to provide truetype font support.

Windows DLL users: although you can use these DLL-exported pointers directly, you cannot easily assign them to other pointers. This will cause hard-to-debug problems. To avoid such troubles, you should call the functions gdFontGetTiny(), gdFontGetSmall(), gdFontGetMediumBold(), gdFontGetLarge(), and gdFontGetGiant() in order to obtain pointers to the fonts under Windows.

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.

Windows DLL users: although you can use these DLL-exported pointers directly, you cannot easily assign them to other pointers. This will cause hard-to-debug problems. To avoid such troubles, you should call the functions gdFontGetTiny(), gdFontGetSmall(), gdFontGetMediumBold(), gdFontGetLarge(), and gdFontGetGiant() in order to obtain pointers to the fonts under Windows.

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, gdFontGetLarge(),
  im->w / 2 - gdFontGetLarge()->h / 2,
  im->h / 2 + (strlen(s) * gdFontGetLarge()->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.

Windows DLL users: although you can use these DLL-exported pointers directly, you cannot easily assign them to other pointers. This will cause hard-to-debug problems. To avoid such troubles, you should call the functions gdFontGetTiny(), gdFontGetSmall(), gdFontGetMediumBold(), gdFontGetLarge(), and gdFontGetGiant() in order to obtain pointers to the fonts under Windows.

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 *gdImageStringFT(gdImagePtr im, int *brect, int fg, char *fontname, double ptsize, double angle, int x, int y, char *string) (FUNCTION)

RECOMMENDED. New in 1.8.4. gdImageStringFT draws text using the FreeType 2.x library.

gdImageStringFT draws a string of anti-aliased characters on the image using the FreeType library to render user-supplied TrueType fonts. We do not provide TrueType fonts (.ttf and .ttc files). Obtaining them is entirely up to you. The string is anti-aliased, meaning that there should be fewer "jaggies" visible. The fontname is the full pathname to a TrueType font file, or a font face name if the GDFONTPATH environment variable or the compiled-in DEFAULT_FONTPATH macro of gdft.c have been set intelligently. In the absence of a full path, the font face name may be presented with or without extension (2.0.26).

The null-terminated string argument is considered to be encoded via the UTF_8 standard; also, HTML entities are supported, including decimal, hexadecimal, and named entities (2.0.26). Those who are passing ordinary ASCII strings may have difficulty with the & character unless encoded correctly as & but should have no other difficulties.

The string may be arbitrarily scaled (ptsize) and rotated (angle in radians). The direction of rotation is counter-clockwise, with 0 radians (0 degrees) at 3 o'clock and PI/2 radians (90 degrees) at 12 o'clock.

The user-supplied int brect[8] array is filled on return from gdImageStringFT with the 8 elements representing the 4 corner coordinates of the bounding rectangle (the smallest rectangle that completely surrounds the rendered string and does not intersect any pixel of the rendered string).

0	lower left corner, X position
1	lower left corner, Y position
2	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: "À"

gdImageStringFT 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 = gdImageStringFT(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 = gdImageStringFT(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);

See also gdImageStringFTEx.

char *gdImageStringFTEx(gdImagePtr im, int *brect, int fg, char *fontname, double ptsize, double angle, int x, int y, gdFTStringExtraPtr strex) (FUNCTION)

New in 2.0.5, also found in common third-party versions of gd. gdImageStringFTEx extends the capabilities of gdImageStringFT by providing a way to pass additional parameters.

If the strex parameter is not null, it must point to a gdFTStringExtra structure. As of gd 2.0.5, this structure is defined as follows:

typedef struct {
       /* logical OR of gdFTEX_ values */
       int flags; 
       /* fine tune line spacing for '\n' */
       double linespacing; 
       /* Preferred character mapping */
       int charmap;
       /* Rendering resolution */
       int hdpi;
       int vdpi;
} gdFTStringExtra, *gdFTStringExtraPtr;

To output multiline text with a specific line spacing, include gdFTEX_LINESPACE in the setting of flags:

flags |= gdFTEX_LINESPACE;

And also set linespacing to the desired spacing, expressed as a multiple of the font height. Thus a line spacing of 1.0 is the minimum to guarantee that lines of text do not collide.

If gdFTEX_LINESPACE is not present, or strex is null, or gdImageStringFT is called, linespacing defaults to 1.05.

To specify a preference for Unicode, Shift_JIS Big5 character encoding, set or To output multiline text with a specific line spacing, include gdFTEX_CHARMAP in the setting of flags:

flags |= gdFTEX_CHARMAP;

And set charmap to the desired value, which can be any of gdFTEX_Unicode, gdFTEX_Shift_JIS, or gdFTEX_Big5. If you do not specify a preference, Unicode will be tried first. If the preferred character mapping is not found in the font, other character mappings are attempted.

GD operates on the assumption that the output image will be rendered to a computer screen. By default, gd passes a resolution of 96 dpi to the freetype text rendering engine. This influences the "hinting" decisions made by the renderer. To specify a different resolution, set hdpi and vdpi accordingly (in dots per inch) and add gdFTEX_RESOLUTION to flags:

flags | gdFTEX_RESOLUTION;

For more information, see gdImageStringFT.

char *gdImageStringFTCircle(gdImagePtr im, int cx, int cy, double radius, double textRadius, double fillPortion, char *font, double points, char *top, char *bottom, int fgcolor) (FUNCTION)

Draws the text strings specified by top and bottom on im, curved along the edge of a circle of radius radius, with its center at cx and cy. top is written clockwise along the top; bottom is written counterclockwise along the bottom. textRadius determines the "height" of each character; if textRadius is 1/2 of radius, characters extend halfway from the edge to the center. fillPortion varies from 0 to 1.0, with useful values from about 0.4 to 0.9, and determines how much of the 180 degrees of arc assigned to each section of text is actually occupied by text; 0.9 looks better than 1.0 which is rather crowded. font is a freetype font; see gdImageStringFT. points is passed to the freetype engine and has an effect on hinting; although the size of the text is determined by radius, textRadius, and fillPortion, you should pass a point size that "hints" appropriately -- if you know the text will be large, pass a large point size such as 24.0 to get the best results. fgcolor can be any color, and may have an alpha component, do blending, etc.

Returns 0 on success, or an error string otherwise.

#include <stdio.h>
#include <gd.h>

int main (int argc, char *argv[])
{
        FILE *in;
        FILE *out;
        gdImagePtr im;
        int radius;
        /* Create an image of text on a circle, with an
                alpha channel so that we can copy it onto a
                background */
        in = fopen("mypicture.jpg", "rb");
        if (!in) {
                im = gdImageCreateTrueColor(300, 300);
        } else {
                im = gdImageCreateFromJpeg(in);
                fclose(in);
        }
        if (gdImageSX(im) < gdImageSY(im)) {
                radius = gdImageSX(im) / 2;
        } else {
                radius = gdImageSY(im) / 2;
        }
        gdStringFTCircle(
                im,
                gdImageSX(im) / 2,
                gdImageSY(im) / 2,
                radius,
                radius / 2,
                0.8,
                "arial",
                24,
                "top text",
                "bottom text",
                gdTrueColorAlpha(240, 240, 255, 32));
        out = fopen("gdfx.png", "wb");
        if (!out) {
                fprintf(stderr, "Can't create gdfx.png\n");
                return 1;
        }
        gdImagePng(im, out);
        fclose(out);
        gdImageDestroy(im);
        return 0;
}

For more information, see gdImageStringFTEx and gdImageSquareToCircle.

char *gdImageStringTTF(gdImagePtr im, int *brect, int fg, char *fontname, double ptsize, double angle, int x, int y, char *string) (FUNCTION)

DEPRECATED. This function simply invokes gdImageStringFT for backwards compatibility with old code that was written with FreeType 1.x.

int gdFontCacheSetup(void) (FUNCTION)

This function initializes the font cache for freetype text output functions such as gdImageStringFTEx. If this function is not called by the programmer, it is invoked automatically on the first truetype text output call, which is perfectly safe unless the application is multithreaded. Multithreaded applications should directly invoke this function before allowing any thread to use freetype text output. Returns 0 on success, nonzero if the freetype library fails to initialize.

void gdFontCacheShutdown(void) (FUNCTION)

This function releases the memory used by the freetype font cache and the text output mutex. Applications that use gd for their entire lifetime, then exit, need not call this function.

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, or an RGBA value in the case of a truecolor image; in either case you can then use the returned value as a parameter to drawing functions. When creating a new palette-based 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, gdImageColorClosest and gdImageColorClosestHWB 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 gdImageColorAllocateAlpha(gdImagePtr im, int r, int g, int b, int a) (FUNCTION)

gdImageColorAllocateAlpha finds the first available color index in the image specified, sets its RGBA values to those requested (255 is the maximum for red, green and blue, and 127 represents full transparency for alpha), and returns the index of the new color table entry, or an RGBA value in the case of a truecolor image; in either case you can then use the returned value as a parameter to drawing functions. When creating a new palette-based 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 palette-based PNG files that already use 256 colors.) Note that gdImageColorAllocateAlpha does not check for existing colors that match your request; see gdImageColorExactAlpha and gdImageColorClosestAlpha for ways to locate existing colors that approximate the color desired in situations where a new color is not available. Also see gdImageColorResolveAlpha.

... 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, 50% transparent. */
red = gdImageColorAllocateAlpha(im, 255, 0, 0, 64);  
/* 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.

When applied to a truecolor image, this function always succeeds in returning the desired color.

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 gdImageColorClosestAlpha(gdImagePtr im, int r, int g, int b, int a) (FUNCTION)

gdImageColorClosest searches the colors which have been defined thus far in the image specified and returns the index of the color with RGBA values closest to those of the request. (Closeness is determined by Euclidian distance, which is used to determine the distance in four-dimensional color/alpha space between colors.)

If no colors have yet been allocated in the image, gdImageColorClosestAlpha returns -1.

When applied to a truecolor image, this function always succeeds in returning the desired color.

This function is most useful as a backup method for choosing a drawing color when a palette-based image already contains gdMaxColors (256) colors and no more can be allocated. (This is not uncommon when working with existing palette-based PNG files that already use many colors.) See gdImageColorExactAlpha 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, 50% transparent, directly */
red = gdImageColorAllocateAlpha(im, 255, 0, 0, 64);  
/* If we fail to allocate red... */
if (red == (-1)) {
  /* Find the closest color instead. */
  red = gdImageColorClosestAlpha(im, 255, 0, 0, 64);
}
/* 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 gdImageColorClosestHWB(gdImagePtr im, int r, int g, int b) (FUNCTION)

gdImageColorClosestHWB searches the colors which have been defined thus far in the image specified and returns the index of the color with hue, whiteness and blackness closest to the requested color. This scheme is typically superior to the Euclidian distance scheme used by gdImageColorClosest.

If no colors have yet been allocated in the image, gdImageColorClosestHWB returns -1.

When applied to a truecolor image, this function always succeeds in returning the desired color.

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 = gdImageColorClosestHWB(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.

When applied to a truecolor image, this function always succeeds in returning the desired 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. */
/* 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.

When applied to a truecolor image, this function always succeeds in returning the desired 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 gdImageColorResolveAlpha(gdImagePtr im, int r, int g, int b, int a) (FUNCTION)

gdImageColorResolveAlpha searches the colors which have been defined thus far in the image specified and returns the index of the first color with RGBA values which exactly match those of the request. If no allocated color matches the request precisely, then gdImageColorResolveAlpha tries to allocate the exact color. If there is no space left in the color table then gdImageColorResolveAlpha returns the closest color (as in gdImageColorClosestAlpha). This function always returns an index of a color.

When applied to a truecolor image, this function always succeeds in returning the desired 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, 50% transparent, or the next best thing */
red = gdImageColorResolveAlpha(im, 255, 0, 0, 64);
/* 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 a palette image. For truecolor images, the result of this call is undefined and should not be used.

int gdImageRed(gdImagePtr im, int c) (MACRO)

gdImageRed is a macro which returns the red portion of the specified color in the image. This macro works for both palette and truecolor images.

int gdImageGreen(gdImagePtr im, int c) (MACRO)

gdImageGreen is a macro which returns the green portion of the specified color in the image. This macro works for both palette and truecolor images.

int gdImageBlue(gdImagePtr im, int c) (MACRO)

gdImageBlue is a macro which returns the blue portion of the specified color in the image. This macro works for both palette and truecolor images.

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. Note that JPEG images do not support transparency, so this setting has no effect when writing JPEG images.

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 (or when you are writing a JPEG-format file, which does not support transparency), 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 PNG 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);

void gdImageTrueColor(int red, int green, int blue) (MACRO)

gdImageTrueColor returns an RGBA color value for use when drawing on a truecolor image. Red, green, and blue are all in the range between 0 (off) and 255 (maximum). This macro should not be used with palette-based images. If you need to write code which is compatible with both palette-based and truecolor images, use gdImageColorResolve.

void gdTrueColorAlpha(int red, int green, int blue, int alpha) (MACRO)

gdTrueColorAlpha returns an RGBA color value for use when drawing on a truecolor image with alpha channel transparency. Red, green, and blue are all in the range between 0 (off) and 255 (maximum). Alpha is in the range between 0 (opaque) and 127 (fully transparent). This macro should not be used with palette-based images. If you need to write code which is compatible with both palette-based and truecolor images, use gdImageColorResolveAlpha.

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 gdImageCopyResampled(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int destW, int destH, int srcW, int srcH) (FUNCTION)

gdImageCopyResampled is used to copy a rectangular portion of one image to another image, smoothly interpolating pixel values so that, in particular, reducing the size of an image still retains a great deal of clarity. 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. For a version which does not interpolate pixel values, see gdImageCopyResized.

Pixel values are only interpolated if the destination image is a truecolor image. Otherwise, gdImageCopyResized is automatically invoked.

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. If the destination image is a palette image, gd will use the gdImageColorResolve function to determine the best color available.

... Inside a function ...
gdImagePtr im_in;
gdImagePtr im_out;
int x, y;
FILE *in;
FILE *out;
/* Load a large png to shrink in the smaller one */
in = fopen("large.png", "rb");
im_in = gdImageCreateFromPng(in);
fclose(in);
/* Make the output image four times as small on both axes. Use
  a true color image so that we can interpolate colors. */
im_out = gdImageCreateTrueColor(im_in->sx / 4, im_in->sy / 4);
/* Now copy the large image, but four times smaller */
gdImageCopyResampled(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 gdImageCopyRotated(gdImagePtr dst, gdImagePtr src, double dstX, double dstY, int srcX, int srcY, int srcW, int srcH, int angle) (FUNCTION)

gdImageCopyRotated is used to copy a rectangular portion of one image to another image, or to another region of the same image. The srcX and srcY coordinates specify the upper left corner of the source area; however, the dstX and dstY coordinates specify the CENTER of the destination area. This important distinction is made because the rotated rectangle may may or may not be parallel to the X and Y axes. The destination coordinates may be floating point, as the center of the desired destination area may lie at the center of a pixel (0.5 pixels) rather than its upper left corner. The angle specified is an integer number of degrees, between 0 and 360, with 0 degrees causing no change, and counterclockwise rotation as the angle increases.

When you copy a region from one location in an image to another location in the same image, gdImageCopyRotated 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 palette-based images do not necessarily have the same color tables, pixels are not simply set to the same color index values to copy them. If the destination image is not a truecolor image, gdImageColorResolveAlpha is used to choose the destination pixel.

... Inside a function ...
gdImagePtr im_in;
gdImagePtr im_out;
int x, y;
int a;
FILE *in;
FILE *out;
/* Load a small png to rotate 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 rotate the smaller image */
for (a = 0; (a < 360); a += 45) {
        double x = cos(a * .0174532925) * gdImageSX(im_out) / 2;
        double y = -sin(a * .0174532925) * gdImageSY(im_out) / 2;
  gdImageCopyRotated(im_out, im_in, 
                gdImageSX(im_out) / 2 + x, 
                gdImageSY(im_out) / 2 + y, 
    0, 0,
                gdImageSX(im_in),
                gdImageSY(im_in),
                a); 
}
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, attempting to match the colors in the target image to the colors in the source palette.

void gdImageSquareToCircle(gdImagePtr im, int radius) (FUNCTION)

im MUST be square, but can have any size. Returns a new image of width and height radius * 2, in which the X axis of the original has been remapped to theta (angle) and the Y axis of the original has been remapped to rho (distance from center). This is known as a "polar coordinate transform." See also gdImageStringFTCircle, which uses this function internally.

void gdImageSharpen(gdImagePtr im, int pct) (FUNCTION)

Sharpens the specified image. pct is a sharpening percentage, and can be greater than 100. Silently does nothing to non-truecolor images. Silently does nothing for pct<0. Transparency/alpha channel are not altered.

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. (When writing JPEG images, interlacing implies generating progressive JPEG files, which are represented as a series of scans of increasing quality. Noninterlaced gd images result in regular [sequential] JPEG data streams.)

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

When a PNG is loaded with gdImageCreateFromPng or a JPEG is loaded with gdImageCreateFromJpeg, interlace will be set according to the setting in the PNG or JPEG file.

Note that many PNG and JPEG viewers and web browsers do not support interlace or the incremental display of progressive JPEGs. However, the interlaced PNG or progressive JPEG 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  -- could also use gdImageJpeg */
gdImagePng(im, out);
fclose(out);
gdImageDestroy(im);

gdFree(void *ptr) (FUNCTION)

gdFree provides a reliable way to free memory allocated by functions such as gdImagePngPtr which return blocks of memory. Use of this function guarantees that the version of free() that is ultimately called will be intended for use with the version of malloc() that originally allocated the block.

Constants

gdAntiAliased (CONSTANT)

Used in place of a color when invoking a line-drawing function such as gdImageLine or gdImageRectangle. When gdAntiAliased is used as the color, the foreground color set with gdImageSetAntiAliased is used, with antialiasing mechanisms to minimize any "jagged" appearance. For more information, see gdImageSetAntiAliased.

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 palette-based PNG file according to the PNG standard, and is also the maximum number of colors in a palette-based gd image. This of course does not apply to truecolor images.

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 "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

The program "pngtogd2.c" is provided as a simple way of converting .png files to .gd2 format.

About the gdIOCtx structure

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); /* Returns 1 on SUCCESS */
        long    (*tell)(struct gdIOCtx*); 

        void    (*free)(struct gdIOCtx*);

} gdIOCtx;

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'. Note: seek must return 1 on SUCCESS and 0 on FAILURE.
If gdImageGd2 is called		Must also have 'seek' and 'tell'.

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