Adding Extensions

One of the most important design points of the GRADD Model is the ability 
to extend or enhance the overall architecture. It is not possible to 
anticipate the changes in future graphics hardware, so we must provide a 
mechanism to extend the architecture in a manner that takes fullest 
advantage of the new hardware. 

There are many ways to extend the GRADD Model. Using the VMI_CMD_EXTENSION 
command, an extension can be written that passes its own defined commands 
to a GRADD. Support for an extension can be added to an existing GRADD, or 
a new GRADD can be written to handle the additional support for a given 
extension.