All Databases MacTech Vol 13-1997

New PrGeneral

Volume Number: 13

Issue Number: 6

Column Tag: develop

The New PrGeneral Version Opcode

by Ingrid Kelly

For the past 12 years, printer driver developers have used the print record's wDev

field in the TPrStl data structure to store their device information. Specifically,

they've consistently used the high-order byte of this field - commonly known as the

wDev ID - to store the device code. Unfortunately, due to the design limitations of the

print record and the wDev field, the Printing Manager allowed for a maximum of only

256 IDs. Surprisingly enough (ha ha), with the expansion of the printer market,

we're running out of numbers! As a result, with LaserWriter driver version 8.4,

we've added a PrGeneral opcode and new structures to the Printing Manager so that

developers can work around this limitation.

Both printer driver and application developers need to add code to support this new

information, but the changes are minimal. Accompanying this column on the MacTech

Web site is a sample application, called PrGeneral Version, that shows you how to

properly retrieve the new version information when your application is looking for

the features of a particular printer driver.

The New PrGeneral Opcode:

kprversionop

LaserWriter driver version 8.4 introduced several new PrGeneral opcodes, including

a new opcode for driver version information: kPrVersionOp. Using kPrVersionOp is

now the recommended way for applications to find out the printer driver currently in

use. Remember that for printer drivers that haven't updated to use this new PrGeneral

opcode, your application needs to keep its wDev-checking code as well.

For more information on the extended print record opcodes introduced with

LaserWriter version 8.4, read the Print Hints column "The All-New LaserWriter

Driver Version 8.4" in develop Issue 27. There you'll find a table that lists all the

other PrGeneral opcodes supported in Apple printer drivers. See the article "Meet

PrGeneral, the Trap That Makes the Most of the Printing Manager" in develop Issue 3

for more information on PrGeneral.

What Printer Driver Developers Need to Know

From now on, Apple's Developer Support Center will assign all printer drivers a wDev

ID of 255. If you have an old wDev ID number (which is less than 255), you should

still use the number you were assigned so that you don't break any applications that

vary their behavior based on your driver's wDev. In addition, you should implement

the new kPrVersionOp opcode as described here so that new applications can take

advantage of it with your driver.

Listing 1 shows the new opcode and structures that you'll need to implement in your

PDEF 7 resource. You need to place your creator type in the driver.creator field of the

TPrVersion structure. You should also place your version number in driver.release so

that application developers know what version of the driver is available.

Listing 1. The new version opcode and structures

enum {
   ...

kPrVersionOp = 22 // LaserWriter version 8.4 and later

only

};

typedef struct {

OSType architecture; // Architecture (for example, 'pwpc',

'm68k')

OSType creator; // Driver's creator type (for

example, 'AAPL')

unsigned longrelease; // Release number (for example,

0x8480)

unsigned longinterfaces; // Interfaces version (for example,

0x8480)

} TVersion;

typedef struct {

short iOpCode; // Must be kPrVersionOp

short iError; // For returning errors

long lReserved; // Reserved, set to 0

TVersion driver; // Driver information

TVersion reserved; // Reserved, set to 0

} TPrVersion;

The release and interfaces fields have the same format as the first long in a 'vers'

resource - that is, the following four 1-byte values: a major version number, a

minor version number, a revision stage (development = 0x20, alpha = 0x40, beta =

0x60, and release = 0x80), and a prerelease version number.

That's all you'll need to do to support the new PrGeneral opcode in your driver - hard

to believe, but true!

What Application Developers Need to Know

Although Apple doesn't recommend that application developers check the wDev field of

the print record, many do. They assume that the wDev value means they can count on

certain features being present in the printer. For instance, many developers assume

that a wDev of 3 means the printer driver supports PostScript. In fact, it indicates

only that the current printer uses the Apple LaserWriter driver. This leaves out the

possibility that a user has a non-Apple PostScript printer driver with an ID of, say,

243.

Even though Apple doesn't recommend that application developers rely on the wDev

field (or the new PrGeneral opcode, for that matter), if you're going to change

application behavior based on the number or creator returned, at least do so properly

so that your applications don't break with future releases of printer drivers. We

recommend that you use the PrGeneral kPrVersionOp opcode, if available, to get the

structure and then check the driver.creator and driver.release fields to

determine the current printer driver and version (see Listing 1). You should also

continue to support the old wDev method for printer drivers that have not yet updated

to the new PrGeneral opcode. For your reference, the PrGeneral Version sample that

accompanies this column shows how to properly retrieve the version and wDev

information.

Go Forth and Print!

As you can see, the changes that printer driver and application developers need to make

to support the new PrGeneral opcode are minimal. We've already adopted this new

method with the LaserWriter version 8.4.x drivers. We hope you will, too!

______________________________

WDEV Registration

Although from now on all printer drivers will be assigned a wDev ID of 255, we still

request that you register your printer driver with Apple's Developer Support Center,

to avoid creator type conflicts. To do so, register at

http://www.devworld.apple.com/dev/wdev/. Here is the information you need to

provide:

• Company name and address

• Contact name, phone number, and e-mail address

• Make and model of device supported (for example, Apple LaserWriter

16/600)

• Type of connection (for example, serial)

• Creator type (for example, 'AAPL')

You'll receive confirmation of your registration within five to ten working days. If you

have questions about wDev registration, write to devsupport@apple.com.

______________________________