Drupal 7 Module Development

Chapter 11
• form callback: If your effect allows users to enter configuration data
(such as the width and height fields in the previous scale example), then this
indicates the function that defines your configuration form. This value is
optional. If your effect does not require any configuration information,
then this key is not necessary.
• summary theme: After your effect is added to a style, you can create a theme
callback which returns customized text to be displayed on the styles admin
screen. For instance, the rotate effect displays the number of degrees that the
user entered. This value is also optional. If you don't provide it, your effect
will display the value you provided in the label key.
As you can see, we have defined three callbacks that we need to create. First, we will
look at our configuration form. It would be nice for users to be able to specify what
text they would like on watermarked images, so we will offer the option to enter
custom text as well as give them an option to indicate what color it should be.
/**
* Form structure for the watermark configuration form.
*
* @param $data
* The current configuration for this watermark effect.
*/
function watermark_form($data) {
$form['text_color'] = array(
'#type' => 'textfield',
'#default_value' => (isset($data['text_color'])) ? $data['text_
color'] : '#FFFFFF',
'#title' => t('Text color'),
'#description' => t('The color of the text to be used for this
watermark. Use web-style hex colors (#FFFFFF for white, #000000 for
black).'),
'#size' => 7,
'#maxlength' => 7,
'#element_validate' => array('image_effect_color_validate'),
);
$form['text'] = array(
'#type' => 'textfield',
'#default_value' => (isset($data['text'])) ? $data['text'] :
'Drupal loves kittens!',
'#title' => t('Watermark text'),
'#description' => t('Text to be written on the image.'),
'#size' => 30,
'#maxlength' => 60,
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