Inside Macintosh: QuickDraw GX Printing Extensions and Drivers /

Chapter 1 - Introduction to Printing Extensions and Drivers / Using Resources to Create Printing Extensions and Printer Drivers

Overriding Printing Messages

When you decide that you need to override a certain printing message in a printing extension or printer driver, you need to follow these three steps:

1. Write the code to implement your override. You can name your override function with whatever name you want. You need to decide whether your override is going to forward the message to other message handlers (partially override) or not forward the message at all (totally override). If you are partially overriding the message, then you must decide at which point in your code to forward the message to other handlers.
2. Add the message name to one of the override ('over') resources that you include with your extension or driver. Each entry in an override resource specifies the QuickDraw GX message ID, the code segment, and the offset of the jump statement
   to that function in the jump table. The override resource is described in the chapter "Printing Resources" in this book.
3. Add a jump statement for your message override to the assembly-language jump table that you must include in the code for your extension or driver.

The chapters "Printing Extensions" and "Printer Drivers" in this book provide examples of message overrides and override resources and describe the jump table.

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