gd 1.7.2

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 images. Invoke gdImageCreate with the x and y dimensions of the desired image. gdImageCreate returns a gdImagePtr to the new image, or NULL if unable to allocate the image. The image must eventually be destroyed using gdImageDestroy().

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

gdImageCreateFromPng(FILE *in) (FUNCTION)
gdImageCreateFromPngCtx(gdIOCtx *in) (FUNCTION)

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

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

gdImageCreateFromPngSource(gdSourcePtr in) (FUNCTION)

gdImageCreateFromPngSource is called to load a PNG from a data source other than a file. Usage is very similar to the gdImageCreateFromPng function, except that the programmer provides a custom data source.

The programmer must write an input function which accepts a context pointer, a buffer, and a number of bytes to be read as arguments. This function must read the number of bytes requested, unless the end of the file has been reached, in which case the function should return zero, or an error has occurred, in which case the function should return -1. The programmer then creates a gdSource structure and sets the source pointer to the input function and the context pointer to any value which is useful to the programmer.

The example below implements gdImageCreateFromPng by creating a custom data source and invoking gdImageCreateFromPngSource.

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

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

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

gdImageCreateFromGd(FILE *in) (FUNCTION)
gdImageCreateFromGdCtx(gdIOCtx *in) (FUNCTION)

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

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

gdImageCreateFromGd2(FILE *in) (FUNCTION)
gdImageCreateFromGd2Ctx(gdIOCtx *in) (FUNCTION)

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

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

gdImageCreateFromGd2Part(FILE *in, int srcX, int srcY, int w, int h) (FUNCTION)
gdImageCreateFromGd2PartCtx(gdIOCtx *in) (FUNCTION)

gdImageCreateFromGd2Part is called to load parts of images from gd2 format files. Invoked in the same way as gdImageCreateFromGd2, but with extra parameters indicating the source (x, y) and width/height of the desired image. gdImageCreateFromGd2Part returns a gdImagePtr to the new image, or NULL if unable to load the image. The image must eventually be destroyed using gdImageDestroy().

gdImageCreateFromXbm(FILE *in) (FUNCTION)

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

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

gdImageCreateFromXpm(FILE *in) (FUNCTION)

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

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

gdImageDestroy(gdImagePtr im) (FUNCTION)

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

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

void gdImagePng(gdImagePtr im, FILE *out) (FUNCTION)

gdImagePng outputs the specified image to the specified file in PNG format. The file must be open for writing. Under MSDOS and all versions of Windows, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under Unix there is no penalty for doing so. gdImagePng does not close the file; your code must do so.

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

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

Identical to gdImagePng except that it returns a pointer to a memory area with the PNG data. This memory must be freed by the caller when it is no longer needed. The 'size' parameter received the total size of the block of memory.

gdImagePngToSink(gdImagePtr im, gdSinkPtr out) (FUNCTION)

gdImagePngToSink is called to write a PNG to a data "sink" (destination) other than a file. Usage is very similar to the gdImagePng function, except that the programmer provides a custom data sink.

The programmer must write an output function which accepts a context pointer, a buffer, and a number of bytes to be written as arguments. This function must write the number of bytes requested and return that number, unless an error has occurred, in which case the function should return -1. The programmer then creates a gdSink structure and sets the sink pointer to the output function and the context pointer to any value which is useful to the programmer.

The example below implements gdImagePng by creating a custom data source and invoking gdImagePngFromSink.

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

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

void gdImageGd(gdImagePtr im, FILE *out) (FUNCTION)

gdImageGd outputs the specified image to the specified file in the gd image format. The file must be open for writing. Under MSDOS and all versions of Windows, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under Unix there is no penalty for doing so. gdImagePng does not close the file; your code must do so.

The gd image format is intended for fast reads and writes of images your program will need frequently to build other images. It is not a compressed format, and is not intended for general use.

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

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

Identical to gdImageGd except that it returns a pointer to a memory area with the GD data. This memory must be freed by the caller when it is no longer needed. The 'size' parameter received the total size of the block of memory.

void gdImageGd2(gdImagePtr im, FILE *out, int chunkSize, int fmt) (FUNCTION)

gdImageGd2 outputs the specified image to the specified file in the gd2 image format. The file must be open for writing. Under MSDOS and all versions of Windows, it is important to use "wb" as opposed to simply "w" as the mode when opening the file, and under Unix there is no penalty for doing so. gdImageGd2 does not close the file; your code must do so.

The gd2 image format is intended for fast reads and writes of parts of images. It is a compressed format, and well suited to retrieving smll sections of much larger images. The third and fourth parameters are the 'chunk size' and format resposectively.

The file is stored as a series of compressed subimages, and the Chunk Size determines the sub-image size - a value of zero causes the GD library to use the default.

It is also possible to store GD2 files in an uncompressed format, in which case the fourth parameter should be GD2_FMT_RAW.

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

void* gdImageGd2Ptr(gdImagePtr im, int chunkSize, int fmt, int *size) (FUNCTION)

Identical to gdImageGd2 except that it returns a pointer to a memory area with the GD2 data. This memory must be freed by the caller when it is no longer needed. The 'size' parameter received the total size of the block of memory.

Drawing Functions

void gdImageSetPixel(gdImagePtr im, int x, int y, int color) (FUNCTION)

gdImageSetPixel sets a pixel to a particular color index. Always use this function or one of the other drawing functions to access pixels; do not access the pixels of the gdImage structure directly.

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

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

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

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

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

gdImageDashedLine is provided solely for backwards compatibility with gd 1.0. New programs should draw dashed lines using the normal gdImageLine function and the new gdImageSetStyle function.

gdImageDashedLine is used to draw a dashed line between two endpoints (x1,y1 and x2, y2). The line is drawn using the color index specified. The portions of the line that are not drawn are left transparent so the background is visible.

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

void gdImagePolygon(gdImagePtr im, gdPointPtr points, int pointsTotal, int color) (FUNCTION)

gdImagePolygon is used to draw a polygon with the verticies (at least 3) specified, using the color index specified. See also gdImageFilledPolygon.

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

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

gdImageRectangle is used to draw a rectangle with the two corners (upper left first, then lower right) specified, using the color index specified.

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

void gdImageFilledPolygon(gdImagePtr im, gdPointPtr points, int pointsTotal, int color) (FUNCTION)

gdImageFilledPolygon is used to fill a polygon with the verticies (at least 3) specified, using the color index specified. See also gdImagePolygon.

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

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

gdImageFilledRectangle is used to draw a solid rectangle with the two corners (upper left first, then lower right) specified, using the color index specified.

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

void gdImageArc(gdImagePtr im, int cx, int cy, int w, int h, int s, int e, int color) (FUNCTION)

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

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

void gdImageFillToBorder(gdImagePtr im, int x, int y, int border, int color) (FUNCTION)

gdImageFillToBorder floods a portion of the image with the specified color, beginning at the specified point and stopping at the specified border color. For a way of flooding an area defined by the color of the starting point, see gdImageFill.

The border color cannot be a special color such as gdTiled; it must be a proper solid color. The fill color can be, however.

Note that gdImageFillToBorder is recursive. It is not the most naive implementation possible, and the implementation is expected to improve, but there will always be degenerate cases in which the stack can become very deep. This can be a problem in MSDOS and MS Windows 3.1 environments. (Of course, in a Unix or Windows 95/98/NT environment with a proper stack, this is not a problem at all.)

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

void gdImageFill(gdImagePtr im, int x, int y, int color) (FUNCTION)

gdImageFill floods a portion of the image with the specified color, beginning at the specified point and flooding the surrounding region of the same color as the starting point. For a way of flooding a region defined by a specific border color rather than by its interior color, see gdImageFillToBorder.

The fill color can be gdTiled, resulting in a tile fill using another image as the tile. However, the tile image cannot be transparent. If the image you wish to fill with has a transparent color index, call gdImageTransparent on the tile image and set the transparent color index to -1 to turn off its transparency.

Note that gdImageFill is recursive. It is not the most naive implementation possible, and the implementation is expected to improve, but there will always be degenerate cases in which the stack can become very deep. This can be a problem in MSDOS and MS Windows environments. (Of course, in a Unix or Windows 95/98/NT environment with a proper stack, this is not a problem at all.)

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

void gdImageSetBrush(gdImagePtr im, gdImagePtr brush) (FUNCTION)

A "brush" is an image used to draw wide, shaped strokes in another image. Just as a paintbrush is not a single point, a brush image need not be a single pixel. Any gd image can be used as a brush, and by setting the transparent color index of the brush image with gdImageColorTransparent, a brush of any shape can be created. All line-drawing functions, such as gdImageLine and gdImagePolygon, will use the current brush if the special "color" gdBrushed or gdStyledBrushed is used when calling them.

gdImageSetBrush is used to specify the brush to be used in a particular image. You can set any image to be the brush. If the brush image does not have the same color map as the first image, any colors missing from the first image will be allocated. If not enough colors can be allocated, the closest colors already available will be used. This allows arbitrary PNGs to be used as brush images. It also means, however, that you should not set a brush unless you will actually use it; if you set a rapid succession of different brush images, you can quickly fill your color map, and the results will not be optimal.

You need not take any special action when you are finished with a brush. As for any other image, if you will not be using the brush image for any further purpose, you should call gdImageDestroy. You must not use the color gdBrushed if the current brush has been destroyed; you can of course set a new brush to replace it.

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

void gdImageSetTile(gdImagePtr im, gdImagePtr tile) (FUNCTION)

A "tile" is an image used to fill an area with a repeated pattern. Any gd image can be used as a tile, and by setting the transparent color index of the tile image with gdImageColorTransparent, a tile that allows certain parts of the underlying area to shine through can be created. All region-filling functions, such as gdImageFill and gdImageFilledPolygon, will use the current tile if the special "color" gdTiled is used when calling them.

gdImageSetTile is used to specify the tile to be used in a particular image. You can set any image to be the tile. If the tile image does not have the same color map as the first image, any colors missing from the first image will be allocated. If not enough colors can be allocated, the closest colors already available will be used. This allows arbitrary PNGs to be used as tile images. It also means, however, that you should not set a tile unless you will actually use it; if you set a rapid succession of different tile images, you can quickly fill your color map, and the results will not be optimal.

You need not take any special action when you are finished with a tile. As for any other image, if you will not be using the tile image for any further purpose, you should call gdImageDestroy. You must not use the color gdTiled if the current tile has been destroyed; you can of course set a new tile to replace it.

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

void gdImageSetStyle(gdImagePtr im, int *style, int styleLength) (FUNCTION)

It is often desirable to draw dashed lines, dotted lines, and other variations on a broken line. gdImageSetStyle can be used to set any desired series of colors, including a special color that leaves the background intact, to be repeated during the drawing of a line.

To use gdImageSetStyle, create an array of integers and assign them the desired series of color values to be repeated. You can assign the special color value gdTransparent to indicate that the existing color should be left unchanged for that particular pixel (allowing a dashed line to be attractively drawn over an existing image).

Then, to draw a line using the style, use the normal gdImageLine function with the special color value gdStyled.

As of version 1.1.1, the style array is copied when you set the style, so you need not be concerned with keeping the array around indefinitely. This should not break existing code that assumes styles are not copied.

You can also combine styles and brushes to draw the brush image at intervals instead of in a continuous stroke. When creating a style for use with a brush, the style values are interpreted differently: zero (0) indicates pixels at which the brush should not be drawn, while one (1) indicates pixels at which the brush should be drawn. To draw a styled, brushed line, you must use the special color value gdStyledBrushed. For an example of this feature in use, see gddemo.c (provided in the distribution).

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

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

/* Destroy it */
gdImageDestroy(im);

Query Functions

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

gdImageBlue is a macro which returns the blue component of the specified color index. Use this macro rather than accessing the structure members directly.

int gdImageGetPixel(gdImagePtr im, int x, int y) (FUNCTION)

gdImageGetPixel() retrieves the color index of a particular pixel. Always use this function to query pixels; do not access the pixels of the gdImage structure directly.

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

int gdImageBoundsSafe(gdImagePtr im, int x, int y) (FUNCTION)

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

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

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

gdImageGreen is a macro which returns the green component of the specified color index. Use this macro rather than accessing the structure members directly.

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

gdImageRed is a macro which returns the red component of the specified color index. Use this macro rather than accessing the structure members directly.

int gdImageSX(gdImagePtr im) (MACRO)

gdImageSX is a macro which returns the width of the image in pixels. Use this macro rather than accessing the structure members directly.

int gdImageSY(gdImagePtr im) (MACRO)

gdImageSY is a macro which returns the height of the image in pixels. Use this macro rather than accessing the structure members directly.

Fonts and text-handling functions

void gdImageChar(gdImagePtr im, gdFontPtr font, int x, int y, int c, int color) (FUNCTION)

gdImageChar is used to draw single characters on the image. (To draw multiple characters, use gdImageString or gdImageString16. See also gdImageStringTTF, new with gd-1.6.2.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts. The character specified by the fifth argument is drawn from left to right in the specified color. (See gdImageCharUp for a way of drawing vertical text.) Pixels not set by a particular character retain their previous color.

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

void gdImageCharUp(gdImagePtr im, gdFontPtr font, int x, int y, int c, int color) (FUNCTION)

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

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

void gdImageString(gdImagePtr im, gdFontPtr font, int x, int y, unsigned char *s, int color) (FUNCTION)

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

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

void gdImageString16(gdImagePtr im, gdFontPtr font, int x, int y, unsigned short *s, int color) (FUNCTION)

gdImageString is used to draw multiple 16-bit characters on the image. (To draw single characters, use gdImageChar.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts. The null-terminated string of characters represented as 16-bit unsigned short integers specified by the fifth argument is drawn from left to right in the specified color. (See gdImageStringUp16 for a way of drawing vertical text.) Pixels not set by a particular character retain their previous color.

This function was added in gd1.3 to provide a means of rendering fonts with more than 256 characters for those who have them. A more frequently used routine is gdImageString.

void gdImageStringUp(gdImagePtr im, gdFontPtr font, int x, int y, unsigned char *s, int color) (FUNCTION)

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

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

void gdImageStringUp16(gdImagePtr im, gdFontPtr font, int x, int y, unsigned short *s, int color) (FUNCTION)

gdImageString is used to draw multiple 16-bit characters vertically on the image. (To draw single characters, use gdImageChar.) The second argument is a pointer to a font definition structure; five fonts are provided with gd, gdFontTiny, gdFontSmall, gdFontMediumBold, gdFontLarge, and gdFontGiant. You must include the files "gdfontt.h", "gdfonts.h", "gdfontmb.h", "gdfontl.h" and "gdfontg.h" respectively and (if you are not using a library-based approach) link with the corresponding .c files to use the provided fonts. The null-terminated string of characters represented as 16-bit unsigned short integers specified by the fifth argument is drawn from bottom to top in the specified color. (See gdImageStringUp16 for a way of drawing horizontal text.) Pixels not set by a particular character retain their previous color.

This function was added in gd1.3 to provide a means of rendering fonts with more than 256 characters for those who have them. A more frequently used routine is gdImageStringUp.

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

gdImageStringTTF is draws a string of anti-aliased characters on the image using the FreeType library to print from user-supplied TrueType fonts. We do not provide TrueType fonts. Obtaining them is entirely up to you. The string is anti-aliased, meaning that there should be less "jaggies." The fontname is the full pathname to a TrueType font file. The string may be arbitrarily scaled (ptsize) and rotated (angle in radians).

The user-supplied int brect[8] array is filled on return from gdImageStringTTF with the 8 elements representing the 4 corner coordinates of the bounding rectangle.

0	lower left corner, X position
lower left corner, Y position
lower right corner, X position
3	lower right corner, Y position
4	upper right corner, X position
5	upper right corner, Y position
6	upper left corner, X position
7	upper left corner, Y position

The points are relative to the text regardless of the angle, so "upper left" means in the top left-hand corner seeing the text horizontally.

Use a NULL gdImagePtr to get the bounding rectangle without rendering. This is a relatively cheap operation if followed by a rendering of the same string, because of the caching of the partial rendering during bounding rectangle calculation.

The string is rendered in the color indicated by the gf color index. Use the negative of the desired color index to disable anti-aliasing.

The string may contain UTF-8 sequences like: "À"

gdImageStringTTF will return a null char* on success, or an error string on failure.

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

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

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

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

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

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

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

/* Destroy it */
gdImageDestroy(im);

Color-handling functions

int gdImageColorAllocate(gdImagePtr im, int r, int g, int b) (FUNCTION)

gdImageColorAllocate finds the first available color index in the image specified, sets its RGB values to those requested (255 is the maximum for each), and returns the index of the new color table entry. When creating a new image, the first time you invoke this function, you are setting the background color for that image.

In the event that all gdMaxColors colors (256) have already been allocated, gdImageColorAllocate will return -1 to indicate failure. (This is not uncommon when working with existing PNG files that already use 256 colors.) Note that gdImageColorAllocate does not check for existing colors that match your request; see gdImageColorExact and gdImageColorClosest for ways to locate existing colors that approximate the color desired in situations where a new color is not available. Also see gdImageColorResolve, new in gd-1.6.2.

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

int gdImageColorClosest(gdImagePtr im, int r, int g, int b) (FUNCTION)

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

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

This function is most useful as a backup method for choosing a drawing color when an image already contains gdMaxColors (256) colors and no more can be allocated. (This is not uncommon when working with existing PNG files that already use many colors.) See gdImageColorExact for a method of locating exact matches only.

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

int gdImageColorExact(gdImagePtr im, int r, int g, int b) (FUNCTION)

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

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

int gdImageColorResolve(gdImagePtr im, int r, int g, int b) (FUNCTION)

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

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

int gdImageColorsTotal(gdImagePtr im) (MACRO)

gdImageColorsTotal is a macro which returns the number of colors currently allocated in the image. Use this macro to obtain this information; do not access the structure directly.

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

gdImageColorRed is a macro which returns the red portion of the specified color in the image. Use this macro to obtain this information; do not access the structure directly.

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

gdImageColorGreen is a macro which returns the green portion of the specified color in the image. Use this macro to obtain this information; do not access the structure directly.

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

gdImageColorBlue is a macro which returns the green portion of the specified color in the image. Use this macro to obtain this information; do not access the structure directly.

int gdImageGetInterlaced(gdImagePtr im) (MACRO)

gdImageGetInterlaced is a macro which returns true (1) if the image is interlaced, false (0) if not. Use this macro to obtain this information; do not access the structure directly. See gdImageInterlace for a means of interlacing images.

int gdImageGetTransparent(gdImagePtr im) (MACRO)

gdImageGetTransparent is a macro which returns the current transparent color index in the image. If there is no transparent color, gdImageGetTransparent returns -1. Use this macro to obtain this information; do not access the structure directly.

void gdImageColorDeallocate(gdImagePtr im, int color) (FUNCTION)

gdImageColorDeallocate marks the specified color as being available for reuse. It does not attempt to determine whether the color index is still in use in the image. After a call to this function, the next call to gdImageColorAllocate for the same image will set new RGB values for that color index, changing the color of any pixels which have that index as a result. If multiple calls to gdImageColorDeallocate are made consecutively, the lowest-numbered index among them will be reused by the next gdImageColorAllocate call.

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

void gdImageColorTransparent(gdImagePtr im, int color) (FUNCTION)

gdImageColorTransparent sets the transparent color index for the specified image to the specified index. To indicate that there should be no transparent color, invoke gdImageColorTransparent with a color index of -1.

The color index used should be an index allocated by gdImageColorAllocate, whether explicitly invoked by your code or implicitly invoked by loading an image. In order to ensure that your image has a reasonable appearance when viewed by users who do not have transparent background capabilities, be sure to give reasonable RGB values to the color you allocate for use as a transparent color, even though it will be transparent on systems that support transparency.

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

Copying and resizing functions

void gdImageCopy(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h) (FUNCTION)

gdImageCopy is used to copy a rectangular portion of one image to another image. (For a way of stretching or shrinking the image in the process, see gdImageCopyResized.)

The dst argument is the destination image to which the region will be copied. The src argument is the source image from which the region is copied. The dstX and dstY arguments specify the point in the destination image to which the region will be copied. The srcX and srcY arguments specify the upper left corner of the region in the source image. The w and h arguments specify the width and height of the region.

When you copy a region from one location in an image to another location in the same image, gdImageCopy will perform as expected unless the regions overlap, in which case the result is unpredictable.

Important note on copying between images: since different images do not necessarily have the same color tables, pixels are not simply set to the same color index values to copy them. gdImageCopy will attempt to find an identical RGB value in the destination image for each pixel in the copied portion of the source image by invoking gdImageColorExact. If such a value is not found, gdImageCopy will attempt to allocate colors as needed using gdImageColorAllocate. If both of these methods fail, gdImageCopy will invoke gdImageColorClosest to find the color in the destination image which most closely approximates the color of the pixel being copied.

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

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

gdImageCopyResized is used to copy a rectangular portion of one image to another image. The X and Y dimensions of the original region and the destination region can vary, resulting in stretching or shrinking of the region as appropriate. (For a simpler version of this function which does not deal with resizing, see gdImageCopy.)

The dst argument is the destination image to which the region will be copied. The src argument is the source image from which the region is copied. The dstX and dstY arguments specify the point in the destination image to which the region will be copied. The srcX and srcY arguments specify the upper left corner of the region in the source image. The dstW and dstH arguments specify the width and height of the destination region. The srcW and srcH arguments specify the width and height of the source region and can differ from the destination size, allowing a region to be scaled during the copying process.

When you copy a region from one location in an image to another location in the same image, gdImageCopy will perform as expected unless the regions overlap, in which case the result is unpredictable. If this presents a problem, create a scratch image in which to keep intermediate results.

Important note on copying between images: since images do not necessarily have the same color tables, pixels are not simply set to the same color index values to copy them. gdImageCopy will attempt to find an identical RGB value in the destination image for each pixel in the copied portion of the source image by invoking gdImageColorExact. If such a value is not found, gdImageCopy will attempt to allocate colors as needed using gdImageColorAllocate. If both of these methods fail, gdImageCopy will invoke gdImageColorClosest to find the color in the destination image which most closely approximates the color of the pixel being copied.

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

void gdImageCopyMerge(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h, int pct) (FUNCTION)

gdImageCopyMerge is almost identical to gdImageCopy, except that it 'merges' the two images by an amount specified in the last parameter. If the last parameter is 100, then it will function identically to gdImageCopy - the source image replaces the pixels in the destination.

If, however, the pct parameter is less than 100, then the two images are merged. With pct = 0, no action is taken.

This feature is most useful to 'highlight' sections of an image by merging a solid color with pct = 50:

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

void gdImageCopyMergeGray(gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX, int srcY, int w, int h, int pct) (FUNCTION)

gdImageCopyMergeGray is almost identical to gdImageCopyMerge, except that when merging images it preserves the hue of the source by converting the destination pixels to grey scale before the copy operation.

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

void gdImagePaletteCopy(gdImagePtr dst, gdImagePtr src) (FUNCTION)

Copies a palette from one image to another, doing it's best to match the colors in the target image to the colors in the source palette.

Miscellaneous Functions

int gdImageCompare(gdImagePtr im1, gdImagePtr im2) (FUNCTION)

gdImageCompare returns a bitmap indicating if the two images are different. The members of the bitmap are defined in gd.h, but the most important is GD_CMP_IMAGE, which indicated that the images will actually appear different when displayed. Other, less important, differences relate to pallette entries. Any difference in the transparent colour is assumed to make images display differently, even if the transparent colour is not used.

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

gdImageInterlace(gdImagePtr im, int interlace) (FUNCTION)

gdImageInterlace is used to determine whether an image should be stored in a linear fashion, in which lines will appear on the display from first to last, or in an interlaced fashion, in which the image will "fade in" over several passes. By default, images are not interlaced.

A nonzero value for the interlace argument turns on interlace; a zero value turns it off. Note that interlace has no effect on other functions, and has no meaning unless you save the image in PNG format; the gd and xbm formats do not support interlace.

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

Note that many PNG viewers and web browsers do not support interlace. However, the interlaced PNG should still display; it will simply appear all at once, just as other images do.

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

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

Constants

gdBrushed (CONSTANT)

Used in place of a color when invoking a line-drawing function such as gdImageLine or gdImageRectangle. When gdBrushed is used as the color, the brush image set with gdImageSetBrush is drawn in place of each pixel of the line (the brush is usually larger than one pixel, creating the effect of a wide paintbrush). See also gdStyledBrushed for a way to draw broken lines with a series of distinct copies of an image.

gdMaxColors(CONSTANT)

The constant 256. This is the maximum number of colors in a PNG file according to the PNG standard, and is also the maximum number of colors in a gd image.

gdStyled (CONSTANT)

Used in place of a color when invoking a line-drawing function such as gdImageLine or gdImageRectangle. When gdStyled is used as the color, the colors of the pixels are drawn successively from the style that has been set with gdImageSetStyle. If the color of a pixel is equal to gdTransparent, that pixel is not altered. (This mechanism is completely unrelated to the "transparent color" of the image itself; see gdImageColorTransparent gdImageColorTransparent for that mechanism.) See also gdStyledBrushed.

gdStyledBrushed (CONSTANT)

Used in place of a color when invoking a line-drawing function such as gdImageLine or gdImageRectangle. When gdStyledBrushed is used as the color, the brush image set with gdImageSetBrush is drawn at each pixel of the line, providing that the style set with gdImageSetStyle contains a nonzero value (OR gdTransparent, which does not equal zero but is supported for consistency) for the current pixel. (Pixels are drawn successively from the style as the line is drawn, returning to the beginning when the available pixels in the style are exhausted.) Note that this differs from the behavior of gdStyled, in which the values in the style are used as actual pixel colors, except for gdTransparent.

gdDashSize (CONSTANT)

The length of a dash in a dashed line. Defined to be 4 for backwards compatibility with programs that use gdImageDashedLine. New programs should use gdImageSetStyle and call the standard gdImageLine function with the special "color" gdStyled or gdStyledBrushed.

gdTiled (CONSTANT)

Used in place of a normal color in gdImageFilledRectangle, gdImageFilledPolygon, gdImageFill, and gdImageFillToBorder. gdTiled selects a pixel from the tile image set with gdImageSetTile in such a way as to ensure that the filled area will be tiled with copies of the tile image. See the discussions of gdImageFill and gdImageFillToBorder for special restrictions regarding those functions.

gdTransparent (CONSTANT)

Used in place of a normal color in a style to be set with gdImageSetStyle. gdTransparent is not the transparent color index of the image; for that functionality please see gdImageColorTransparent.

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);
        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'.
If gdImageGd2 is called		Must also have 'seek' and 'tell'.

Please tell us you're using gd!

Be sure to read this manual carefully first.

Alphabetical quick index

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