Creating and Drawing Images
For now, let’s start with the simplest possible GD example. Example 9-1 is a script that generates a black-filled square. The code works with any version of GD that supports the PNG image format.
Example 9-1. A black square on a white background (black.php)
<?
php
$image
=
imagecreate
(
200
,
200
);
$white
=
imagecolorallocate
(
$image
,
0xFF
,
0xFF
,
0xFF
);
$black
=
imagecolorallocate
(
$image
,
0x00
,
0x00
,
0x00
);
imagefilledrectangle
(
$image
,
50
,
50
,
150
,
150
,
$black
);
header
(
"Content-Type: image/png"
);
imagepng
(
$image
);
Example 9-1 illustrates the basic steps in generating any image: creating the image, allocating colors, drawing the image, and then saving or sending the image. Figure 9-1 shows the output of Example 9-1.
Figure 9-1. A black square on a white background
To see the result, simply point your browser at the black.php page. To embed this image in a web page, use:
<img
src=
"black.php"
/>
The Structure of a Graphics Program
Most dynamic image-generation programs follow the same basic steps outlined in Example 9-1.
You can create a 256-color image with the imagecreate()
function, which returns an image
handle:
$image = imagecreate(width
,height
);
All colors used in an image must be allocated with the
imagecolorallocate()
function. The
first color allocated becomes the background color for the
image[4]:
$color = imagecolorallocate(image
,red
,green
,blue
);
The arguments ...
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