Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hplabs!hpfcso!hpfcdq!stroyan
From: stroyan@hpfcdq.HP.COM (Mike Stroyan)
Newsgroups: comp.sys.hp
Subject: Re: Picking from device independendent Starbase Display List
Message-ID: <350021@hpfcdq.HP.COM>
Date: 13 Dec 89 01:14:15 GMT
References: <1053@esatst.yc.estec.nl>
Organization: Hewlett-Packard - Fort Collins, CO
Lines: 21

>Is it possible to pick from a device independent display list? 

Yes.

>As a first guess I assume that the only way to do it is to traverse
>the display list, issuing display_segment calls and checking for hits
>on the pick aperture, but how do I get the correct segment when using
>hidden surface removal? Do I have to traverse the list twice?

The Starbase device independent display list supports pick_from_segment,
but it does not support hidden surface removal.  You could use a display
device's Z buffer by starting hit mode on the display device and using
display_segment or display_element calls seperated by inquire_hit calls
as you described.  You would need to traverse the list once to set up
the Z buffer and once again to test for hits.  This is discussed in the
hit_mode(3G) manual entry.

The same double traversal is performed inside a pick_from_segment from a
display list on a device which has hidden_surface enabled.

Mike Stroyan, stroyan@hpfcla.hp.com