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From: Emmanuel Astier <emmanuel.astier@wi...>  20020227 12:36:09

But that only works if the light+mesh move is small enougth. You can't insure every edge of the silhouette at trame t as a common triangle with a edge at trame t1 ? And if you're using quad, it's very possible that the silhouette edge come from one of the quad edge to the quad opposite edge... * /* / * * * * * * * * * \ * \* * Here if the light moves ( in the quad world ) is orthogonal to the '*' edges, the silhouette will jump from the first * edge to the second... Am I completely wrong ??? Emmanuel > Original Message > From: Willem H. de Boer [mailto:Willem@...] > Sent: mercredi 27 f=E9vrier 2002 13:10 > To: Ulf Ochsenfahrt; GDAlgorithms List > Subject: RE: [2] [Algorithms] Generating Shadow Volumes with open > geometry >=20 >=20 > "start with the {edge list} of the=20 > last frame and if an edge of the last frame is not a silhouette=20 > edge in this frame, check the edges it connects to." >=20 > Oh, I think I should point out that with {edge list} I mean > the silhouette edge list, not the entire mesh's edge list >=20 > Original Message > From: Ulf Ochsenfahrt [mailto:ulfjack@...] > Sent: 27 February 2002 11:32 > To: GDAlgorithms List > Subject: RE:[2] [Algorithms] Generating Shadow Volumes with open > geometry >=20 >=20 > I think I'd do this differently. >=20 > What about this: > Put in a bit flag for each triangle which show which way the=20 > triangle is > facing. Whenever a triangle changes, you check the adjacent edges. > Some of the are then moved out of the silhouette edges list and some > are inserted. >=20 > This may be more accurate if you have concave objects. >=20 >  Ulf. >=20 > "Willem H. de Boer" <Willem@...> wrote on 27/02/02 10:31:22: > > > >Well, one way of going about speeding up edge detection, would > >be temporal coherence. So, calculate the silhouette edges for > >the shadowcasting object the expensive way (some winged edge > >structure, find the edges connecting a backfacing triangle > >with a frontfacing one), and store it in a list. Then for the=20 > >next frame, or after T frames, start with the edge list of the=20 > >last frame and if an edge of the last frame is not a silhouette=20 > >edge in this frame, check the edges it connects to. This saves=20 > >a lot of edge tracking; more efficient with higher temporal=20 > coherence. > > > >Cheers, > > > >Willem > >MuckyFoot Goat Boy > > > >Original Message > >From: Chris Perry [mailto:perry@...] > >Sent: 27 February 2002 08:16 > >To: gdalgorithmslist@... > >Subject: RE: [Algorithms] Generating Shadow Volumes with=20 > open geometry > > > > > >if a triangle is facing the light, then you can safely=20 > extrude any edges > >that=20 > >either have no neighbor or have a neighbor that is not=20 > facing the light. > > > >It's funny, I'm actually working on shadow volumes right now=20 > and I was > >trying to think of a way to speed up the edge detection process. It > >wouldn't > >work on objects with holes, but if you knew you had a solid object > >you could theoretically trace one edge to the next until you came=20 > >full circle, right? limiting the search space to only child edges. > >I've been wasting too much time trying to create a tree=20 > structure that > >links them together in a way which won't produce endless circles. I=20 > >think you have to treat the edges as symbolic vectors and keep=20 > >a "head" to "tail" orientation... i.e. an edge is a child if=20 > it's "tail" is > >the > >parent edge's "head"... hmmm...who knows, maybe it's impossible... > > > >Chris Perry > >Angel Studios > > > > > > > >Original Message > >From: Jason Zisk [SMTP:ziskj@...] > >Sent: Tuesday, February 26, 2002 8:32 PM > >To: gdalgorithmslist@... > >Subject: [Algorithms] Generating Shadow Volumes with=20 > open geometry > > > >Quick question about shadow volumes. A lot of our geometry=20 > is "open", for > >instance a cylinder with no top or bottom. When generating=20 > a shadow volume > >for it, what do you do with the triangle edges that aren't=20 > shared between > >two triangles when it comes to checking if the edge is a=20 > silhouette? With > >two triangles you just see if one is facing the light and=20 > one isnt, then > >extrude that edge. With only one triangle, do you simply=20 > check if the > >triangle is backfacing, if so extrude? I'd like to hear=20 > what others do in > >this situation. > > > >Thanks, > > > >  Jason Zisk > > nFusion Interactive LLC > > > > > > > > > >_______________________________________________ > >GDAlgorithmslist mailing list > >GDAlgorithmslist@... > >https://lists.sourceforge.net/lists/listinfo/gdalgorithmslist > >Archives: > >http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 > > > >_______________________________________________ > >GDAlgorithmslist mailing list > >GDAlgorithmslist@... > >https://lists.sourceforge.net/lists/listinfo/gdalgorithmslist > >Archives: > >http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 > > > >_______________________________________________ > >GDAlgorithmslist mailing list > >GDAlgorithmslist@... > >https://lists.sourceforge.net/lists/listinfo/gdalgorithmslist > >Archives: > >http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 >=20 >=20 >=20 > _______________________________________________ > GDAlgorithmslist mailing list > GDAlgorithmslist@... > https://lists.sourceforge.net/lists/listinfo/gdalgorithmslist > Archives: > http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 >=20 > _______________________________________________ > GDAlgorithmslist mailing list > GDAlgorithmslist@... > https://lists.sourceforge.net/lists/listinfo/gdalgorithmslist > Archives: > http://sourceforge.net/mailarchive/forum.php?forum_id=3D6188 >=20 