If you have a non Tablet application and you’re thinking about selling it in the Tablet community, your application will probably work fine as is. Even without any changes. That’s because the Tablet PC OS is a superset of XP.
However, for graphical, user-intensive applications there is one difference that deserves special mention. Many of these non-Tablet apps work OK, but they may experience so-so user interaction with the pen. They’ll work fine with the mouse though.
Without any changes to your application, the user will be able to use the pen with it because the pen movements are automatically translated into equivalent mouse events for you. But there are some things that you may have to account for to provide a great user experience.
For instance, when using a stylus, sometimes there are so many synthesized mouse events coming in and if the app is trying to perform a lot of operations for each mouse movement, the UI can get behind. I’ve seen this problem with some legacy CAD products.
Also, even though the Tablet OS automatically generates equivalent mouse events for the stylus there is one noticable difference, particularly when performing freehand drawing. If the stylus is initially moved rapidly in a circular motion, the first part of the curve will be rendered as a straight line. The problem is that the first pen movements are dropped. For instance, if you’re using a brush in Photoshop and you move the stylus rapidly in a circular motion, you’ll more likely than not get a straight segment at the beginning of each curve. Alternatively, let’s say you want the user to use a freehand drawing tool (that responds to mouse events) to handwrite words or for annotation. If the user writes at normal speeds, the beginnings of most pen movements will be dropped. You’ll particularly notice this when writing printed or block characters. It’s less pronounced with cursive handwriting because there are fewer pen up/down events.
Now, in each case if the user slows down and draws or writes slowly the problem is mitigated. However, I’ve found that this is hard to do. The pen is so efficient at drawing that you naturally want to go fast.
Unfortunately, there are not hard and fast rules here. You’ll have to try each application on a case-by-case basis to decide if the stylus is OK for you or not.