UniqueID and XUID

C makes it easy to shoot yourself in the foot;

C++ makes it harder, but when you do,

it blows away your whole leg.”

—Bjarne Stroustrup

From: Thomas Phinney of Adobe

Subject: [OpenType] Why you don’t need UniqueIDs

Date: Fri, 04 Mar 2005 10:04:41 -0800

Neither Type 1 nor OpenType CFF fonts require PostScript UniqueIDs.

Back in the mid-80s, when printing might be done on a 57K serial connection

and printers might have 8 MHz processors, the caching of device-generated

bitmaps enabled by UniqueIDs made a noticeable speed difference. With today’s

connection bandwidths and printers, the printing speed difference was

insignificant in our tests (conducted around 2002), and certainly not enough

to outweigh the risks of collisions between UniqueIDs for different fonts and

the trouble of tracking the ID numbers.

For these reasons, Adobe stopped using UniqueIDs (and XUIDs) in our own

OpenType CFF fonts. If we still made Type 1 fonts, we wouldn’t use UniqueIDs

for them, either.

You may of course continue to use UniqueIDs, it’s just that they are not

necessary.

Regards,

T

Thomas W. Phinney

Program Manager

Fonts & Core Technologies

Adobe Systems