Using PHP's GD library

Using PHP's GD library

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Using PHP's GD library

The GD library is included in php versions >= 4.3.0. It is an image library, that lets you create static or dynamic images, such as the ones you see in some people's profiles, stating their rank. The GD library works in much the same way to other imaging libraries. You start by defining a canvas or a set size, then had a variety of functions available to you to create shapes and text on the canvas.

Creating a canvas

You can create a variety of canvases, starting with either a blank canvas, or a previous image as the background. A common staring canvas can be created with the following code:

$im = imagecreate(400,320); imagecolorallocate($im, 255, 255, 255);

This creates a canvas ($im) which is 400px x 320px, with a white background. All colors in GD are inputed as RGB values, so (255,255,255) is white, and (0,0,0) is black. You could also start with an existing .png file with this code:

$im = imagecreatefrompng("bg.png");

Similar commands exist for other image formats, such as .gif, .jpg/.jpeg, and it even supports loading an image from a variable as a string.

Drawing

Once you have a canvas, you can begin to draw on it. Some common functions to draw are:

imageline — Draw a line imageellipse — Draw an ellipse imagerectangle — Draw a rectangle imagepolygon — Draws a polygon

With these functions, you can draw almost any shape you like. There are also 'filled' variations for each, so for example, there is imagefilledellipse. The only one which doesn't have a 'filled' equivalent is imageline (for hopefully obvious reasons).

Text

For creating text, you can either use GD's inbuild fonts:

imagestring — Draw a string horizontally

Or a postscript font of your choosing, which must be loaded with imagepsloadfont, then used with imagepstext.

Copying images

Occasionally, you might want to include another image in your code. This is entirely possible, using this command:

imagecopy — Copy part of an image

Note You must use this function after you have created your text and drawings, anything you draw afterwards will not be shown! It took me a while to work that one out :D

Finalizing your image and cleaning up

Once you have drawn your image, you must send the correct headers to the browser, and then send the image code for the browser to display it. This is usually done with the following 2 lines (for a png image):

header("Content-type: image/png"); imagepng($im);

You can the free up the resources used in creating the images by disposing of any fonts you might have loaded, and destroying both the image you were creating and any images you may have imported. Assuming you did not load fonts or additional images, you can do this with the following line:

imagedestroy($im);

That pretty much wraps up the basics. You can find more indepth information on GD, as well as syntax at: http://uk3.php.net/manual/en/book.image.php

Below is some sample code I wrote to help you piece together making a simple image with PHP and GD.

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Running this code generated this image:

http://img27.imageshack.us/img27/5297/shapesphp.png