Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!mit-eddie!bloom-beacon!LARRY.MCRCIM.MCGILL.EDU!mouse
From: mouse@LARRY.MCRCIM.MCGILL.EDU
Newsgroups: comp.windows.x
Subject: Re:  Substituting tablet for mouse
Message-ID: <9012091744.AA15646@Larry.McRCIM.McGill.EDU>
Date: 9 Dec 90 17:44:56 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 40

> I'd like to be able to use a tablet with a pressure-sensitive stylus
> in place of a mouse on my workstation.

It will be difficult to do this with X.  How do you propose to
implement WarpPointer requests?  Some mysterious force from the
workstation grabs the stylus and shoves it over to where it's been
warped to?

I suppose if you're willing to yank the pointer back to where the
stylus really is when a client warps it away, you could do this, but it
seems contrary to the spirit of XWarpPointer() to do that.  Not that
that makes it illegal.

> My goal is to have the tablet and stylus behave just like a mouse for
> all unwitting applications, but to make it possible for my
> applications to look for the pressure information in the event
> structure, and use that.

You're going to have to define a new event type.  The current event
structure does not have anywhere to put this information.  You say

> [Can I] cram the stylus pressure into the high two bytes of the
> 'state' field in the motion event structure?  The Xlib manual shows
> this field as being unsigned int, and the most of the low order 16
> bits are defined as various button and modifier key masks.  Can I I
> use the high 16 bits for pressure?

but the protocol uses a 16-bit field for this (check out the encoding
in Appendix B).  Expanding it by two more bytes would be an
incompatible change and therefore is highly unlikely to happen.

Your best bet, I would say, is to implement it as an extension.  If no
real pointer device is available, you could have it front for one, more
or less ignoring warps (more precisely, warping right back again), but
I'd consider that as a sort of desperation move.

					der Mouse

			old: mcgill-vision!mouse
			new: mouse@larry.mcrcim.mcgill.edu