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From: erik@abblund.se (Erik Sparre)
Newsgroups: comp.windows.x
Subject: How do I pick/hit graphical primitives in X ?
Message-ID: <1991Mar15.100902.16094@abblund.se>
Date: 15 Mar 91 10:09:02 GMT
Sender: erik@abblund.se (Erik Sparre)
Organization: ABB Corporate Research, Lund, Sweden
Lines: 23


When you develop a direct manipulation graphical user interface you
will sooner or later need the ability to detect whether the user pointed
at a certain graphical object (line, ect, circle).

I've seen hardware that supports this by letting you set up a very small clip
window around the cursor hot-spot, redraw all primitives (without
actually doing any drawing). As soon as a primitive draws something inside 
the clip window, a flag is raised and/or an interrupt is signaled.
A straightforward and pretty fast method since no display memory is updated
during the redraw.

Some toolkits/systems, like GKS, supports picking as a part of the API. 

Is there any good way to detect picking in X or any X-based library
without having to do the calculations yourself ?

Thanks
-- 
Erik Sparre                                  | Email erik@abblund.se
ABB Corporate Research                       | Phone +46 46 168527
Dept. KLL, Lab for Man-Machine Communication | Telex        33709
IDEON Research Park, S-223 70 LUND, SWEDEN   | Fax   +46 46 145620