WordPress at a glance
filter is not described

template_directory filter-hook . WP 1.5.0

Filters the current theme directory path.

Usage

add_filter( 'template_directory', 'filter_function_name_8613', 10, 3 );
function filter_function_name_8613( $template_dir, $template, $theme_root ){
	// filter...

	return $template_dir;
}
$template_dir(string)
The URI of the current theme directory.
$template(string)
Directory name of the current theme.
$theme_root(string)
Absolute path to the themes directory.

Where the hook is called

get_template_directory()
wp-includes/theme.php 317
return apply_filters( 'template_directory', $template_dir, $template, $theme_root );

Where the hook is used (in WP core)

Does not used.