Question

I am working on a legacy project in VC++/Win32/MFC. Recently it became a requirement that the application work on a tablet pc, and this ushered in a host of new issues. I have been able to work with, and around these issues, but am left with one wherein I could use some expert suggestions.

I have a particular bug that is induced by the ‘lift’ of the stylus off of the active surface. Basically the mouse cursor disappears and then reappears when you ‘press’ it back onto the screen.

It makes sense that this is unaccounted for in the application. you can’t lift the cursor on a desktop pc. So what I am looking for is a good overview on what happens (in terms of windows messages, etc.) when the lift occurs. Does this translate to just focus changes and mouseover events? My bug seems to also involve cursor changes (may not be lift related though). Certainly the unexpected ‘lift’ is breaking the state of the application’s tool processing.

So the tangible questions are:

1. What happens when a stylus ‘lift’ occurs? A press?
2. What API calls can be used to detect this? Does it just translate into standard messages with flags/values set?
3. Whats a good way to test/emulate this when your development pc is a desktop? Am I just flying blind here? (I only have periodic access to a tablet pc)
4. What represents correct behavior or best practice for tablet stylus awareness?

Thanks for your consideration, ee

Answer 1

As a tablet user I can answer a few of your questions.

First:

You cannot very easily keep a ‘keyboard focus’ on a window when the stylus has to trail out of the focused window to push a key on the virtual keyboard.

Most of the virtual keyboards I’ve used (The windows tablet input panel and one under ubuntu) allow the program they are typing in to keep ‘keyboard focus.’

What happens when a stylus ‘lift’ occurs? A press?

Under Windows, the pressure value drops, but outside of that, there is no event. (I don’t know about linux.)

What API calls can be used to detect this? Does it just translate into standard messages with flags/values set?

As mentioned above, if you can get the pressure value, you can use that.

Whats a good way to test/emulate this when your development pc is a desktop? Am I just flying blind here? (I only have periodic access to a tablet pc)

When the stylus is placed down elsewhere, the global coordinates of the pointer change, so, you can emulate the sudden pointer move with anything that allows you to change the global pointer values. (The Robot class in Java makes this fairly easy.)

What represents correct behavior or best practice for tablet stylus awareness?

I’d recommend you read what Microsoft has to say, the MSDN website has a number of excellent articles. (http://msdn.microsoft.com/en-us/library/ms704849(VS.85).aspx) I’ll point out that the size of the buttons on your applications makes a HUGE difference.

Hope this was of help.