How to write a function of total price

Question

I am using a function to show custom information on an invoice: (app/code/core/Mage/Sales/Model/Order/Pdf/invoice.php)

public function customtext($page)
{    
    $page->drawText(Mage::helper('sales')->__('custom text '), 35, $this->y, 'UTF-8');
}

Added at end of invoice.php, and $this->customtext($page); added to end of public function getPdf($invoices = array()) above $this->_afterGetPdf();

But I want to include in my custom text the value of 20% of my invoice Grand Total. How is this done?

Answer 1

if you can pass yo your function the invoice object you are displaying you can do it like this:

public function customtext($page, $invoice)
{    
    $price = $invoice->getGrandTotal() * 20 /100;
    $order = $invoice->getOrder();
    $page->drawText(Mage::helper('sales')->__($order->formatPriceTxt($price)), 35, $this->y, 'UTF-8');
}