Output Determination in SD

Hi,

this is a simple question, but I wanted to understand it before implementing the change. I know how to add a custom output determination type in SPRO and how to create a smartform or sapscript to print an invoice. My question is again, simple.

The configuration asks for a program name and program routine. When developing standalone forms we usually create an abap program that retrieves all necessary information and then triggers the sapscript or smartform, passing the variables/tables. In this particular scenario, the print will be triggered when printing and invoice. My questions are: how is the interface between the abap program and form being triggered? Since the config asks for the program name and the routine, should we hardcode the form name inside the code? The parameter for this abap program should be the invoice number, only?

I hope I make myself clear and you can understand me. It has been a long time since I've done an output determination and I really don't remember it.

Thanks,

Julio F.