Hello,
That function is part of the PHP GD module.
GD is required by HikaSerial (and HikaShop) for image processing.
But, GD module might not include all its functions, such as functions regarding text processing (TrueType fonts)
See :
www.php.net/manual/en/function.imagettfbbox.php
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.