Page 205 - Open Soource Technologies 304.indd

Open Source Technologies

Notes The fifth parameter is for the text to print, and the final parameter the colour of the text.
This is the same colour that was allocated earlier using imagecolorallocate().
• Drawing a Line and Setting the Thickness of the Brush

The imageline() function can be used to draw a line to the image. To set the thickness of
the brush used to draw the line, you may want to call the imagesetthickness() function
as I did in my example. The numeric parameter to imagesetthickness() is the thickness of
the brush in pixels. If you don’t call imagesetthickness(), the line will be 1 pixel thick.

The imageline() function is called with the start and end coordinates of the line, in x,y
format. The line starts from 30,45 and ends on 165,45. That is, it will be a horizontal line 45
pixels from the top, starting 30 pixels from the left edge and ending 165 pixels from that
same edge. Since $line_colour was set to a shade of green earlier, the line will be green.

• How to Output the Image
Since the output of example script is the image itself, send an “image/png” content type
header to the browser telling it that what follows are the bytes of a PNG image. The
function imagepng() is then called to generate the necessary image from $my_img image
identifer. If you prefer to save your image, don’t call the header() function to output the
header, and call imagepng() with the filename of the image for its second parameter, like
the following:

imagepng( $my_img, “my_new_image.png” );
Your image does not have to be a PNG image. You can use imagegif() or imagejpeg() to
create GIF and JPG images respectively. You should of course send the correct content
type header for the type of image you are creating. For example, a jpeg image should
have a content type of “image/jpeg” while a gif image “image/gif”. Note though that
GIF support may or may not necessarily be compiled into the version of the GD library
your web host is using, so if you’re not sure, use one of the other file formats.

• Freeing Resources
On completion, the program releases the resources associated with the image by
callingimagecolordeallocate() and imagedestroy().

Colours are represented by three digits, known as the RGB value. The first
digit denotes the red component, the second the green and the third blue.
These colours are used for web pages as well as numerous other computer
applications.
The fonts have various sizes, ranging from 1 to 5, where 1 is the smallest font
size and 5 the largest.

12.2 Necessary Modifications to PHP

Current versions of the PHP distribution include a bundled version of GD graphics library. The
inclusion of this library eliminates the need to download and install several third-party libraries,
but this library will need to be activated at installation time.

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