The Printing Buffer Structure(IM:XP)

Inside Macintosh: QuickDraw GX Printing Extensions and Drivers /

Chapter 4 - Printing Messages / Printing Messages Reference

The Printing Buffer Structure
The printing buffer structure, of data type gxPrintingBuffer, holds the document data that QuickDraw GX sends to the printer. It is used with the GXDumpBuffer and GXFreeBuffer messages, which are described in the section "Device Communications Messages" beginning on page 4-131.
struct gxPrintingBuffer {
   long     size;
   long     userData;
   char     data[1];
};
typedef struct gxPrintingBuffer gxPrintingBuffer;
Field Description

size
The number of bytes in the buffer.
userData
The signature for this buffer, into which a message handler can write a unique ID. If you are writing a driver and overriding the GXDumpBuffer and GXFreeBuffer messages, you can use this value to match your buffers.
data
The data in the buffer. This is an array containing size bytes.