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From: newsuser@oliver.SUBLINK.ORG (Ugo Cei)
Newsgroups: comp.windows.x
Subject: Re: Using tablets in X (Was: Re: Moving pointer in software ?)
Message-ID: <919@oliver.SUBLINK.ORG>
Date: 21 Mar 91 21:38:45 GMT
References: <9103131557.AA10051@devnull.Eng.Sun.COM> <1165@dandelion.CI.COM> <1991Mar18.170530.13580@dsd.es.com> <1276@attc.UUCP>
Organization: Oliver, Pavia, Italy
Lines: 51

marbru@attc.UUCP (Martin Brunecky) writes:

>In article <1991Mar18.170530.13580@dsd.es.com> rthomson@dsd.es.com (Rich Thomson) writes:
>>In article <1165@dandelion.CI.COM>
>>	dale@jack.ci.com (Dale Gallaher) writes:
>>>   Has anyone implemented applications which use tablet input instead
>>>   of the mouse.  We have a CAD package where many uses prefer using
>>>   a tablet but I have never seen anyone discuss using tablets in X.
>>
>>The X input extension allows input from a wide variety of devices.
>>However, the support for the input extension must be built into the
>>server (including driving the devices).  It is not plug-and-play in
>>that respect.
>>

>   We have taken a slightly different approach. Since we want to treate
>   the digitizer suface similarly to the screen, i.e. lay windows on the
>   top of it, get enter/leave/button/motion events etc., we decided
>   to strip-down (lobotomize) the MIT X Server.

You could also use a much more simple-minded approach: warp the
pointer when the stylus or the mouse on the digitizer moves. You could
create a program which reads the stylus position and outputs a couple
of coordinates whenever the position changes. Your application has to
open a connection to this program (e.g. using popen) and make the
server listen to it (via XtAddInput). I've tried this and it worked,
even though movement of the pointer either lagged behind the actual
movement of the stylus (too many coordinates being input) or the
movement wasn't smooth enough when I tried to output them less
frequently. Eventually, I obtained satisfying performance by disposing
entirely of XtAddInput and warping the pointer from the program
connected to the digitizer, like this:

	while(forever) {
		read coordinates from digitizer
		if(they have changed)
			warp pointer to the new location
	}

You also need to generate fake ButtonPress/Release events (via
XSendEvent) when the user presses/releases the stylus or mouse
button(s). If you send these events to the root window instead of your
application's main window, you can control the entire X session using
the digitizer, but beware that many applications require a three
button mouse to work properly and even some key+button combinations.
Also, when you stop moving the digitizer, you regain control of the
pointer through the mouse.
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