Drupal 7 Module Development

Chapter 11
Finally we can make the modification to our image:
/**
* Image effect callback; add a text watermark to an image.
*
* @param $image
* An image object returned by image_load().
* @param $data
* An array of attributes to use when performing the
* watermark effect.
* @return
* TRUE on success. FALSE on failure.
*/
function watermark_effect(&$image, $data) {
$data['text_color'] = str_replace('#', '', $data['text_color']);
$red = hexdec(substr($data['text_color'], 0, 2));
$green = hexdec(substr($data['text_color'], 2, 2));
$blue = hexdec(substr($data['text_color'], 4));
}
$color = imagecolorallocate($image->resource, $red, $green, $blue);
imagestring($image->resource, 5, 5, 5, $data['text'], $color);
From a Drupal perspective, the important thing is that our effect callback,
watermark_effect(), takes two arguments. The first is an image object just like
we've encountered earlier, which contains a resource handle we can pass to GD
functions for modification. The second is the data array just like the one passed to
our configuration form callback, containing an associative array of user submitted
configuration information. This array is keyed on the field names as specified in the
form callback above. We use the information in $data to properly format our text.
Beyond that this functionality is pretty straightforward. Most of the code is
concerned with properly formatting the color information. In the first four lines we
convert the hex color submitted by the user (found in $data['text_color']) to the
RGB decimal values which we will need later. We do this by parsing each individual
hex value of the string and using hexdec() to convert them to their decimal
equivalent.
The rest of the code relates to the image creation functionality from the GD
image library. We will cover this briefly but for more details refer to the GD
documentation at:
http://in2.php.net/manual/en/book.image.php
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