Holy cow, I wrote a book!
Last time, we saw one example of a "decoy" used in the service of
application compatibility with respect to the Printers Control Panel.
Today we'll look at another decoy, this time for the Display Control Panel.
When support for multiple monitors was being developed,
a major obstacle was that a large number of display drivers
hacked the Display Control Panel directly instead of using
the documented extension mechanism.
For example, instead of adding a separate page to the Display
Control Panel's property sheet for, say, virtual desktops,
they would just hack into the "Settings" page and add their
Some drivers were so adventuresome as to do what seemed like
a total rewrite of the "Settings" page.
They would take all the controls, move them around, resize them,
hide some, show others, add new buttons of their own,
and generally speaking treat the page as a lump of clay waiting
to be molded into their own image.
(Here's a handy rule of thumb:
If your technique works only if the user speaks English,
you probably should consider the possibility that what you're doing
is relying on an implementation detail rather than something
that will be officially supported going forward.)
In order to support multiple monitors, the Settings page on the
Display Control Panel underwent a major overhaul.
But when you tried to open the Display Control Panel on a
system that had one of these aggressive drivers installed,
it would crash because the driver ran around rearranging things
like it always did,
even though the things it was manipulating weren't what the developers
of the driver intended!
The solution was to create a "decoy" Settings page that looked
exactly like the classic Windows 95 Settings page.
The decoy page's purpose in life was to act as bait for these
aggressive display drivers and allow itself to be abused
mercilessly, letting the driver have its way.
Meanwhile, the real Settings page (which is the one that was
shown to the user), by virtue of having been overlooked,
remained safe and unharmed.
There was no attempt to make this decoy Settings page do anything
interesting at all.
Its sole job was to soak up mistreatment without complaining.
As a result, those drivers lost whatever nifty features their
shenanigans were trying to accomplish, but at least the Display
Control Panel stayed alive and allowed the user to do what they
were trying to do in the first place: Adjust their display settings.