Drupal 7 Module Development

Working with Files and Images
Creating image effects
Note that this example is not compatible with pluggable image libraries,
and will only work with GD. For more information about making
your image functions compatible with multiple libraries, see the API
documentation on image_toolkit_invoke() at:
http://api.drupal.org/api/function/image_toolkit_
invoke/7
We will begin with the assumption that you have created a standard module .info
file with all the information needed for a module named watermark. The first step in
creating a new image effect is implementing hook_image_effect_info().
/**
* Implements hook_image_effect_info().
*/
function watermark_image_effect_info() {
$effects = array();
$effects['watermark'] = array(
'label' => t('Watermark'),
'help' => t('Add a watermark to an image.'),
'effect callback' => 'watermark_effect',
'form callback' => 'watermark_form',
'summary theme' => 'watermark_summary',
);
return $effects;
}
This kind of hook should look pretty familiar by now. It is very similar to
hook_menu(), which was discussed in Chapter 5, Building an Admin Interface. We
create an associative array of the effects that we are defining, and return it to the
caller. The array is keyed by a unique identifier, in our case, watermark. This array
contains the following information about our image effect:
• label: The label that will be used in the effects drop-down on the styles
page. This text will also be used after you have added your effect, if you
have not defined a summary theme below.
• help: A text description of what your effect does.
• effect callback: A function that will be called to actually execute your
effect on an image. This function name indicates where your image
manipulation code will go.
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