GD.pm - Manual
NAME
GD.pm - Interface to Gd Graphics Library
DESCRIPTION
The gd graphics library
The gd graphics library, written by Thomas Boutell of Cold
Spring Harbor Labs (Boutell@netcom.com), is a package of C
routines for creating, reading, writing, and manipulating
GIF graphics files. It provides graphics primitives for:
o Reading and writing GIF files.
o Drawing lines, rectangles, arcs, ellipses and text.
o Flood fills.
o Using arbitrary images as tiled patterns for filling shapes.
o Using arbitrary images as paintbrushes.
o resizing it.
o Stamping a portion of one image onto another, optionally
o Simple text rendering.
gd can be obtained at URL http://siva.cshl.org/gd/gd.html.
Directions for installing it, and full documentation are
available from that site.
The GD.pm interface
GD.pm is a port of the gd library by Lincoln Stein
(lstein@genome.wi.mit.edu). It is similar to the original C
library, but contains some modifications to take advantage
of perl's object-oriented features. It defines the
following three classes:
GD::Image
An image class, which holds the image data and accepts
graphic primitive method calls.
GD::Font
A font class, which holds static font information and
used for text rendering.
GD::Polygon
A simple polygon object, used for storing lists of
vertices prior to rendering a polygon into an image.
A Simple Example:
#!/usr/local/bin/perl
use GD;
# create a new image
$im = new GD::Image(100,100);
# allocate some colors
$white = $im->colorAllocate(255,255,255);
$black = $im->colorAllocate(0,0,0);
$red = $im->colorAllocate(255,0,0);
$blue = $im->colorAllocate(0,0,255);
# make the background transparent and interlaced
$im->transparent($white);
$im->interlaced('true');
# Put a black frame around the picture
$im->rectangle(0,0,99,99,$black);
# Draw a blue oval
$im->arc(50,50,95,75,0,360,$blue);
# And fill it with red
$im->fill(50,50,$red);
# Convert the image to GIF and print it on standard output
print $im->gif;
Notes:
GD::Image, passing it the width and height of the image you want
to create. An image object will be returned. Other class
methods allow you to initialize an image from a preexisting GIF,
GD or XBM file.
1. To create a new, empty image, send a new() message to
table. colors are added using a colorAllocate() method call. The
three parameters in each call are the red, green and blue (rgb)
triples for the desired color. The method returns the index of
that color in the image's color table. You should store these
indexes for later use.
2. Next you will ordinarily add colors to the image's color
are described below. In this example, we do some text drawing,
create an oval, and create and draw a polygon.
3. Now you can do some drawing! The various graphics primitives
can add points to the returned polygon one at a time using the
addPt() method. The polygon can then be passed to an image for
rendering.
4. Polygons are created with a new() message to GD::Polygon. You
format by sending it a gif() message. It will return a
(potentially large) scalar value containing the binary data for
the image. Ordinarily you will print it out at this point or
write it to a file.
5. When you're done drawing, you can convert the image into GIF
Method Calls
Creating and Saving Images
new GD::Image::new(width,height) [class method]
To create a new, blank image, send a[new() message to
the GD::Image class. For example:
$myImage = new GD::Image(100,100) || die;
This will create an image that is 100 x 100 pixels
wide. If you don't specify the dimensions, a default
of 64 x 64 will be chosen. If something goes wrong
(e.g. insufficient memory), this call will return
undef.
newFromGif
GD::Image::newFromGif(FILEHANDLE) [class method]
This will create an image from a GIF file read in
through the provided filehandle. The filehandle must
previously have been opened on a valid GIF file or
pipe. If successful, this call will return an
initialized image which you can then manipulate as you
please. If it fails, which usually happens if the
thing at the other end of the filehandle is not a valid
GIF file, the call returns undef. Notice that the call
doesn't automatically close the filehandle for you.
To get information about the size and color usage of
the information, you can call the image query methods
described below.
Example usage:
open (GIF,"barnswallow.gif") || die;
$myImage = newFromGif GD::Image(GIF) || die;
close GIF;
newFromXbm
GD::Image::newFromXbm(FILEHANDLE) [class method]
This works in exactly the same way as newFromGif, but
reads the contents of an X Bitmap file:
open (XBM,"coredump.xbm") || die;
$myImage = newFromXbm GD::Image(XBM) || die;
close XBM;
newFromGd
GD::Image::newFromGd(FILEHANDLE) [class method]
This works in exactly the same way as newFromGif, but
reads the contents of a GD file. GD is Tom Boutell's
disk-based storage format, intended for the rare case
when you need to read and write the image to disk
quickly. It's not intended for regular use, because,
unlike GIF or JPEG, no image compression is performed
and these files can become BIG.
open (GDF,"godzilla.gd") || die;
$myImage = newFromGd GD::Image(GDF) || die;
close GDF;
gif GD::Image::gif [object method]
This returns the image data in GIF format. You can
then print it, pipe it to a display program, or write
it to a file. Example:
$gif_data = $myImage->gif;
open (DISPLAY,"| display -") || die;
print DISPLAY $gif_data;
close DISPLAY;
gd GD::Image::gd [object method]
This returns the image data in GD format. You can then
print it, pipe it to a display program, or write it to
a file. Example:
print MYOUTFILE $myImage->gd;
Color Control
colorAllocate
GD::Image::colorAllocate(red,green,blue) [object method]
This allocates a color with the specified red, green
and blue components and returns its index in the color
table, if specified. The first color allocated in this
way becomes the image's background color.
(255,255,255) is white (all pixels on). (0,0,0) is
black (all pixels off). (255,0,0) is fully saturated
red. (127,127,127) is 50% gray. You can find plenty
of examples in /usr/X11/lib/X11/rgb.txt.
If no colors are allocated, then this function returns
-1.
Example:
$white = $myImage->colorAllocate(0,0,0); #background color
$black = $myImage->colorAllocate(255,255,255);
$peachpuff = $myImage->colorAllocate(255,218,185);
colorDeallocate
GD::Image::colorDeallocate(colorIndex) [object method]
This marks the color at the specified index as being
ripe for reallocation. The next time colorAllocate is
used, this entry will be replaced. You can call this
method several times to deallocate multiple colors.
There's no function result from this call.
Example:
$myImage->colorDeallocate($peachpuff);
$peachy = $myImage->colorAllocate(255,210,185);
colorClosest
GD::Image::colorClosest(red,green,blue) [object method]
This returns the index of the color closest in the
color table to the red green and blue components
specified. If no colors have yet been allocated, then
this call returns -1.
Example:
$apricot = $myImage->colorClosest(255,200,180);
colorExact
GD::Image::colorExact(red,green,blue) [object method]
This returns the index of a color that exactly matches
the specified red green and blue components. If such a
color is not in the color table, this call returns -1.
$rosey = $myImage->colorExact(255,100,80);
warn "Everything's coming up roses.\n" if $rosey >= 0;
colorsTotal
GD::Image::colorsTotal) [object method]
This returns the total number of colors allocated in
the object.
$maxColors = $myImage->colorsTotal;
getPixel
GD::Image::getPixel(x,y) [object method]
This returns the color table index underneath the
specified point. It can be combined with[rgb() to
obtain the rgb color underneath the pixel.
Example:
$index = $myImage->getPixel(20,100);
($r,$g,$b) = $myImage->rgb($index);
rgb GD::Image::rgb(colorIndex) [object method]
This returns a list containing the red, green and blue
components of the specified color index.
Example:
@RGB = $myImage->rgb($peachy);
transparent
GD::Image::transparent(colorIndex) [object method]
This marks the color at the specified index as being
transparent. Portions of the image drawn in this color
will be invisible. This is useful for creating
paintbrushes of odd shapes, as well as for making GIF
backgrounds transparent for displaying on the Web.
Only one color can be transparent at any time. To
disable transparency, specify -1 for the index.
If you call this method without any parameters, it will
return the current index of the transparent color, or
-1 if none.
Example:
open(GIF,"test.gif");
$im = newFromGif GD::Image(GIF);
$white = $im->colorClosest(255,255,255); # find white
$im->transparent($white);
print $im->gif;
Special Colors
GD implements a number of special colors that can be used to
achieve special effects. They are constants defined in the
GD:: namespace, but automatically exported into your
namespace when the GD module is loaded.
setBrush
gdBrushed
GD::Image::setBrush( ) and GD::gdBrushed
You can draw lines and shapes using a brush pattern.
Brushes are just images that you can create and
manipulate in the usual way. When you draw with them,
their contents are used for the color and shape of the
lines.
To make a brushed line, you must create or load the
brush first, then assign it to the image using
setBrush. You can then draw in that with that brush
using the gdBrushed special color. It's often useful
to set the background of the brush to transparent so
that the non-colored parts don't overwrite other parts
of your image.
Example:
# Create a brush at an angle
$diagonal_brush = new GD::Image(5,5);
$white = $diagonal_brush->allocateColor(255,255,255);
$black = $diagonal_brush->allocateColor(0,0,0);
$diagonal_brush->transparent($white);
$diagonal_brush->line(0,4,4,0,$black); # NE diagonal
# Set the brush
$myImage->setBrush($diagonal_brush);
# Draw a circle using the brush
$myImage->arc(50,50,25,25,0,360,gdBrushed);
setStyle
gdStyled
GD::Image::setStyle(@colors) and GD::gdStyled
Styled lines consist of an arbitrary series of repeated
colors and are useful for generating dotted and dashed
lines. To create a styled line, use setStyle to
specify a repeating series of colors. It accepts an
array consisting of one or more color indexes. Then
draw using the gdStyled special color. Another special
color, gdTransparent can be used to introduce holes in
the line, as the example shows.
Example:
# Set a style consisting of 4 pixels of yellow,
# 4 pixels of blue, and a 2 pixel gap
$myImage->setStyle($yellow,$yellow,$yellow,$yellow,
$blue,$blue,$blue,$blue,
gdTransparent,gdTransparent);
$myImage->arc(50,50,25,25,0,360,gdStyled);
To combine the gdStyled and gdBrushed behaviors, you
can specify gdStyledBrushed. In this case, a pixel
from the current brush pattern is rendered wherever the
color specified in[setStyle() is neither gdTransparent
nor 0.
gdTiled
Draw filled shapes and flood fills using a pattern.
The pattern is just another image. The image will be
tiled multiple times in order to fill the required
space, creating wallpaper effects. You must call
setTile in order to define the particular tile pattern
you'll use for drawing when you specify the gdTiled
color. details.
gdStyled
The gdStyled color is used for creating dashed and
dotted lines. A styled line can contain any series of
colors and is created using the setStyled command.
Drawing Commands
setPixel
GD::Image::setPixel(x,y,color) [object method]
This sets the pixel at (x,y) to the specified color
index. No value is returned from this method. The
coordinate system starts at the upper left at (0,0) and
gets larger as you go down and to the right. You can
use a real color, or one of the special colors
gdBrushed, gdStyled and gdStyledBrushed can be
specified.
Example:
# This assumes $peach already allocated
$myImage->setPixel(50,50,$peach);
line GD::Image::line(x1,y1,x2,y2,color) [object method]
This draws a line from (x1,y1) to (x2,y2) of the
specified color. You can use a real color, or one of
the special colors gdBrushed, gdStyled and
gdStyledBrushed.
Example:
# Draw a diagonal line using the currently defind
# paintbrush pattern.
$myImage->line(0,0,150,150,gdBrushed);
dashedLine
GD::Image::dashedLine(x1,y1,x2,y2,color) [object method]
This draws a dashed line from (x1,y1) to (x2,y2) in the
specified color. A more powerful way to generate
arbitrary dashed and dotted lines is to use the
[setStyle() method described below and to draw with the
special color gdStyled.
Example:
$myImage->dashedLine(0,0,150,150,$blue);
rectangle
GD::Image::rectangle(x1,y1,x2,y2,color) [object method]
This draws a rectangle with the specified color.
(x1,y1) and (x2,y2) are the upper left and lower right
corners respectively. Both real color indexes and the
special colors gdBrushed, gdStyled and gdStyledBrushed
are accepted.
Example:
$myImage->rectangle(10,10,100,100,$rose);
filledRectangle
GD::Image::filledRectangle(x1,y1,x2,y2,color) [object method]
This draws a rectangle filed with the specified color.
You can use a real color, or the special fill color
gdTiled to fill the polygon with a pattern.
Example:
# read in a fill pattern and set it
open(GIF,"happyface.gif") || die;
$tile = newFromGif GD::Image(GIF);
$myImage->setTile($tile);
# draw the rectangle, filling it with the pattern
$myImage->filledRectangle(10,10,150,200,gdTiled);
polygon
GD::Image::polygon(polygon,color) [object method]
This draws a polygon with the specified color. The
polygon must be created first (see below). The polygon
must have at least three vertices. If the last vertex
doesn't close the polygon, the method will close it for
you. Both real color indexes and the special colors
gdBrushed, gdStyled and gdStyledBrushed can be
specified.
Example:
$poly = new GD::Polygon;
$poly->addPt(50,0);
$poly->addPt(99,99);
$poly->addPt(0,99);
$myImage->polygon($poly,$blue);
filledPolygon
GD::Image::filledPolygon(poly,color) [object method]
This draws a polygon filled with the specified color.
You can use a real color, or the special fill color
gdTiled to fill the polygon with a pattern.
Example:
# make a polygon
$poly = new GD::Polygon;
$poly->addPt(50,0);
$poly->addPt(99,99);
$poly->addPt(0,99);
# draw the polygon, filling it with a color
$myImage->filledPolygon($poly,$peachpuff);
arc GD::Image::arc(cx,cy,width,height,start,end,color)
[object method]
This draws arcs and ellipses. (cx,cy) are the center
of the arc, and (width,height) specify the width and
height, respectively. The portion of the ellipse
covered by the arc are controlled by start and end,
both of which are given in degrees from 0 to 360. Zero
is at the top of the ellipse, and angles increase
clockwise. To specify a complete ellipse, use 0 and
360 as the starting and ending angles. To draw a
circle, use the same value for width and height.
You can specify a normal color or one of the special
colors gdBrushed, gdStyled, or gdStyledBrushed.
Example:
# draw a semicircle centered at 100,100
$myImage->arc(100,100,50,50,0,180,$blue);
fill GD::Image::fill(x,y,color) [object method]
This method flood-fills regions with the specified
color. The color will spread through the image,
starting at point (x,y), until it is stopped by a pixel
of a different color from the starting pixel (this is
similar to the "paintbucket" in many popular drawing
toys). You can specify a normal color, or the special
color gdTiled, to flood-fill with patterns.
Example:
# Draw a rectangle, and then make its interior blue
$myImage->rectangle(10,10,100,100,$black);
$myImage->fill(50,50,$blue);
GD::Image::fillToBorder(x,y,bordercolor,color) [object method]
Like fill, this method flood-fills regions with the
specified color, starting at position (x,y). However,
instead of stopping when it hits a pixel of a different
color than the starting pixel, flooding will only stop
when it hits the color specified by bordercolor. You
must specify a normal indexed color for the
bordercolor. However, you are free to use the gdTiled
color for the fill.
Example:
# This has the same effect as the previous example
$myImage->rectangle(10,10,100,100,$black);
$myImage->fillToBorder(50,50,$black,$blue);
Image Copying Commands
Two methods are provided for copying a rectangular region
from one image to another. One method copies a region
without resizing it. The other allows you to stretch the
region during the copy operation.
With either of these methods it is important to know that
the routines will attempt to flesh out the destination
image's color table to match the colors that are being
copied from the source. If the destination's color table is
already full, then the routines will attempt to find the
best match, with varying results.
copy GD::Image::copy(sourceImage,dstX,dstY,srcX,srcY,width,height)
[object method]
This is the simpler of the two copy operations, copying
the specified region from the source image to the
destination image (the one performing the method call).
(srcX,srcY) specify the upper left corner of a
rectangle in the source image, and (width,height) give
the width and height of the region to copy.
(dstX,dstY) control where in the destination image to
stamp the copy. You can use the same image for both
the source and the destination, but the source and
destination regions must not overlap or strange things
will happen.
Example:
$myImage = new GD::Image(100,100);
... various drawing stuff ...
$srcImage = new GD::Image(50,50);
... more drawing stuff ...
# copy a 25x25 pixel region from $srcImage to
# the rectangle starting at (10,10) in $myImage
$myImage->copy($srcImage,10,10,0,0,25,25);
copyResized
GD::Image::copyResized(sourceImage,dstX,dstY,srcX,srcY,destW,destH,srcW,srcH)
[object method]
This method is similar to copy() but allows you to
choose different sizes for the source and destination
rectangles. The source and destination rectangle's are
specified independently by (srcW,srcH) and
(destW,destH) respectively. copyResized() will stretch
or shrink the image to accomodate the size
requirements.
Example:
$myImage = new GD::Image(100,100);
... various drawing stuff ...
$srcImage = new GD::Image(50,50);
... more drawing stuff ...
# copy a 25x25 pixel region from $srcImage to
# a larger rectangle starting at (10,10) in $myImage
$myImage->copyResized($srcImage,10,10,0,0,50,50,25,25);
Character and String Drawing
Gd allows you to draw characters and strings, either in
normal horizontal orientation or rotated 90 degrees. These
routines use a GD::Font object, described in more detail
below. There are four built-in fonts, available in global
variables gdLargeFont, gdMediumBoldFont, gdSmallFont and
gdTinyFont. Currently there is no way of dynamically
creating your own fonts.
string
GD::Image::string(font,x,y,string,color) [object method]
This method draws a string startin at position (x,y) in
the specified font and color. Your choices of fonts
are gdSmallFont, gdMediumBoldFont, gdTinyFont and
gdLargeFont.
Example:
$myImage->string(gdSmallFont,2,10,"Peachy Keen",$peach);
stringUp
GD::Image::stringUp(font,x,y,string,color) [object method]
Just like the previous call, but draws the text rotated
counterclockwise 90 degrees.
char
charUp
GD::Image::char(font,x,y,char,color) [object method]
GD::Image::charUp(font,x,y,char,color) [object method]
These methods draw single characters at position (x,y)
in the specified font and color. They're carry-overs
from the C interface, where there is a distinction
between characters and strings. Perl is insensible to
such subtle distinctions.
Miscellaneous Image Methods
interlaced
GD::Image::interlaced( ) GD::Image::interlaced(1)
[object method]
This method sets or queries the image's interlaced
setting. Interlace produces a cool venetian blinds
effect on certain viewers. Provide a true parameter to
set the interlace attribute. Provide undef to disable
it. Call the method without parameters to find out the
current setting.
getBounds
GD::Image::getBounds( ) [object method]
This method will return a two-member list containing
the width and height of the image. You query but not
change the size of the image once it's created.
Polygon Methods
A few primitive polygon creation and manipulation methods
are provided. They aren't part of the Gd library, but I
thought they might be handy to have around (they're borrowed
from my qd.pl Quickdraw library).
c
GD::Polygon::new [class method]
Create an empty polygon with no vertices.
$poly = new GD::Polygon;
addPt
GD::Polygon::addPt(x,y) [object method]
Add point (x,y) to the polygon.
$poly->addPt(0,0);
$poly->addPt(0,50);
$poly->addPt(25,25);
$myImage->fillPoly($poly,$blue);
getPt
GD::Polygon::getPt(index) [object method]
Retrieve the point at the specified vertex.
($x,$y) = $poly->getPt(2);
setPt
GD::Polygon::setPt(index,x,y) [object method]
Change the value of an already existing vertex. It is
an error to set a vertex that isn't already defined.
$poly->setPt(2,100,100);
deletePt
GD::Polygon:deletePt(index) [object method]
Delete the specified vertex, returning its value.
($x,$y) = $poly->deletePt(1);
length
GD::Polygon::length [object method]
Return the number of vertices in the polygon.
$points = $poly->length;
vertices
GD::Polygon::vertices [object method]
Return a list of all the verticies in the polygon
object. Each membver of the list is a reference to an
(x,y) array.
@vertices = $poly->vertices;
foreach $v (@vertices)
print join(",",@$v),"\n";
}
bounds
GD::Polygon::bounds [object method]
Return the smallest rectangle that completely encloses
the polygon. The return value is an array containing
the (left,top,right,bottom) of the rectangle.
($left,$top,$right,$bottom) = $poly->bounds;
offset
GD::Polygon::offset(dx,dy) [object method]
Offset all the vertices of the polygon by the specified
horizontal (dh) and vertical (dy) amounts. Positive
numbers move the polygon down and to the right.
$poly->offset(10,30);
map GD::Polygon::map(srcL,srcT,srcR,srcB,destL,dstT,dstR,dstB)
[object method]
Map the polygon from a source rectangle to an
equivalent position in a destination rectangle, moving
it and resizing it as necessary. See polys.pl for an
example of how this works. Both the source and
destination rectangles are given in
(left,top,right,bottom) coordinates. For convenience,
you can use the polygon's own bounding box as the
source rectangle.
# Make the polygon really tall
$poly->map($poly->bounds,0,0,50,200);
Font Utilities
Gd's support for fonts is minimal. Basically you have
access to gdSmallFont and gdLargeFont for drawing, and not
much else. However, for future compatibility, I've made the
fonts into perl objects of type GD::Font that you can query
and, perhaps someday manipulate.
gdSmallFont
GD::Font::gdSmallFont[constant
This is the basic small font, "borrowed" from a well
known public domain 6x12 font.
gdLargeFont
GD::Font::gdLargeFont[constant
This is the basic large font, "borrowed" from a well
known public domain 8x16 font.
gdMediumBoldFont
GD::Font::gdMediumBoldFont[constant
This is a bold font intermediate in size between the
small and large fonts, borrowed from a public domain
7x13 font;
gdTinyFont
GD::Font::gdTinyFont [constant]
This is a tiny, almost unreadable font, 5x8 pixels
wide.
nchars
GD::Font::nchars [object method]
This returns the number of characters in the font.
print "The large font contains ",gdLargeFont->nchars," characters\n";
offset
GD::Font::offset [object method]
This returns the ASCII value of the first character in
the font
width
height
GD::Font::width GD::Font::height [object methods]
These return the width and height of the font.
($w,$h) = (gdLargeFont->width,gdLargeFont->height);
Copyright Information
The GD.pm interface is copyright 1995, Lincoln D. Stein.
You are free to use it for any purpose, commercial or
noncommercial, provided that if you redistribute the source
code this statement of copyright remains attached. The gd
library is covered separately under a 1994 copyright by
Quest Protein Database Center, Cold Spring Harbor Labs. For
usage information see the gd documentation at URL
http://www.boutell.com/gd/
The latest versions of the perl interface are available at
http://www-genome.wi.mit.edu/ftp/pub/software/WWW/GD.html
ftp://ftp-genome.wi.mit.edu/pub/software/WWW/GD.pm.tar.Z