The "odd" algorithm you're referring to is bilinear interpolation which essentially defines a hyperbolic paraboloid (the simplest surface) through 4 non-coplanar points (i.e. the infamous quad).
For intersection purposes in OSG, it's good that it breaks the quad up into two triangles. Planes are easier to intersect than bilinear surfaces... -Shayne -----Original Message----- From: osg-users-boun...@lists.openscenegraph.org [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Mike Garrity Sent: Thursday, August 04, 2011 8:24 AM To: OpenSceneGraph Users Subject: Re: [osg-users] intersection with quad mesh: only 3 verticesreturned > From: osg-users-boun...@lists.openscenegraph.org [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Tueller, Shayne R Civ USAF AFMC 519 SMXS/MXDEC > Sent: Tuesday, August 02, 2011 4:49 PM > To: osg-users@lists.openscenegraph.org > Subject: Re: [osg-users] intersection with quad mesh: only 3 verticesreturned > > It is true that QUAD is an OpenGL primitive but the GL driver tessellates it into two triangles > underneath the hood. > Most (all?) cards today do break them into 2 tris, but nothing in the OpenGL spec says that they have to, or specifies exactly how they should do it. The reason is that the original SGI geometry engine did not split them. It drew quads directly with an odd algorithm for interpolating values across the interior. Quad lives on as a historical quirk, like the panda's thumb. -Mike Garrity -The MathWorks _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.or g _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
