When developing for a tablet PC, how do I determine if the user clicked a mouse or a pen?

Question

How do I check if the user clicked with a mouse or with a pen stylus on a C# control.

For eg. If the user clicks a text box with a pen button then I want an input panel to pop up but if he clicks with a mouse then it shouldn't. So how do I check whether he was using a mouse or a pen?

Edit: Using Windows Forms not WPF

Answer 1

I wrote an article for MSDN that never got published, I guess because Tablet PC development fizzled out by the time I got it to them. But it described how to do this. Long story short, you'll want the GetMessageExtraInfo API. Here's the definitions:

// [DllImport( "user32.dll" )]
// private static extern uint GetMessageExtraInfo( );

uint extra = GetMessageExtraInfo();
bool isPen = ( ( extra &  0xFFFFFF00 ) == 0xFF515700 );

Email me at my first name at Einstein Tech dot net if you want me to send you the article.