Create Custom Watermark Placeholders

Creating custom watermark placeholders extends Easy Watermark's functionality with personalized dynamic content for your WordPress watermarks. This developer guide shows how to build PHP classes that generate custom placeholder values for advanced watermarking scenarios.

Each placeholder is defined with a class responsible for replacing a specific string tag with a dynamic value. Placeholder class needs to extend EasyWatermark\Placeholders\Abstracts\Placeholder and should implement the following methods:

1. resolve - returning the value of the placeholder
2. validate - checking if the value is correct
3. sanitize - sanitizing the value

There are also 4 abstract placeholders available that implement the validate and sanitize methods for a given value type:

1. EasyWatermark\Placeholders\Abstracts\EmailPlaceholder
2. EasyWatermark\Placeholders\Abstracts\IntegerPlaceholder
3. EasyWatermark\Placeholders\Abstracts\StringPlaceholder
4. EasyWatermark\Placeholders\Abstracts\UrlPlaceholder

Placeholder class

use EasyWatermark\Placeholders\Abstracts\StringPlaceholder;

/**
 * Abstract placeholder
 */
class FavoriteColorPlaceholder extends StringPlaceholder {

	/**
	 * Constructor
	 *
	 * @return void
	 */
	public function __construct() {

		$this->slug    = 'favorite_color';
		$this->name    = __( 'Favorite color', 'textdomain' );
		$this->example = __( 'blue', 'textdomain' );

	}

	/**
	 * Resolves placeholder
	 *
	 * @param  EasyWatermark\Placeholders\Resolver $resolver Placeholders resolver instance.
	 * @return string
	 */
	public function resolve( $resolver ) {

		$user = wp_get_current_user();
		return get_user_meta( 'favorite_color', $user->ID );

	}
}

The above class will replace a %favorite_color% string in the watermark text with the value of a favorite_color meta for logged-in user.

Registering the Placeholder

/**
 * @param EasyWatermark\Placeholders\Resolver $resolver Placeholders resolver instance.
 */
add_action( 'easy-watermark/placeholders/load', function ( $resolver ) {
    // Add custom placeholder instance to the resolver.
    $resolver->add_placeholder( new FavoriteColorPlaceholder() );
} );