[osg-users] Normal bindings and triangle strips
Greetings All, Is it possible to define a normal for every triangle without using primitive type TRIANGLES? For instance, if I am using TRIANGLE_STRIP, what is the effect of setting normals with BIND_PER_PRIMITIVE? And why does BIND_PER_VERTEX seem so wrong on a triangle strip? If the triangle strip faces are not radically different I guess it works ok. But it seems impossible to declare normal vectors precisely when using triangle strips. Am I missing something obvious? Thanks, John Argentieri Software Engineer GENERAL DYNAMICS C4 Systems [EMAIL PROTECTED] ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Normal bindings and triangle strips
Hi John -- I think normals with BIND_PER_PRIMITIVE on a N-triangle strip would mean you have N-2 normals. As we discussed previously, you'll use the OpenGL slow path (albeit stored in a display list) so the effective OpenGL calls would be: glVertex3f glVertex3f glNormal3f // normal for first triangle glVertex3f glNormal3f // normal for second triangle glVertex3f glNormal3f // normal for third triangle glVertex3f ...etc... This should result in a typical faceted appearance (with glShadeModel set to GL_FLAT). However, if you want smooth shading, you'll want to use BIND_PER_VERTEX of course. Which brings us to the next topic... I'm not sure why you are having problems with BIND_PER_VERTEX in a tri strip. It works just like BIND_PER_VERTEX with any other primitive type. Perhaps you could provide more information about the problem you're encountering. You say it works OK if the faces aren't radically different but I'm not sure why you'd use BIND_PER_VERTEX if you were not trying to get a smooth-shaded result. What type of surface are you trying to render, anyway? Do you encounter the same issue in a vanilla OpenGL app? Paul Martz Skew Matrix Software LLC http://www.skew-matrix.com http://www.skew-matrix.com/ +1 303 859 9466 _ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Argentieri, John-P63223 Sent: Wednesday, October 08, 2008 12:34 PM To: [EMAIL PROTECTED] Subject: [osg-users] Normal bindings and triangle strips Greetings All, Is it possible to define a normal for every triangle without using primitive type TRIANGLES? For instance, if I am using TRIANGLE_STRIP, what is the effect of setting normals with BIND_PER_PRIMITIVE? And why does BIND_PER_VERTEX seem so wrong on a triangle strip? If the triangle strip faces are not radically different I guess it works ok. But it seems impossible to declare normal vectors precisely when using triangle strips. Am I missing something obvious? Thanks, John Argentieri Software Engineer GENERAL DYNAMICS C4 Systems [EMAIL PROTECTED] ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Normal bindings and triangle strips
Paul, I'm just trying to learn how it works. If the way you've described it is in fact how I can give each triangle its own normal in a triangle strip, then I thank you my friend. I hope that this is how it works in OSG when using tri strip and bind per primitive. What about bind per vertex and tri strips? Can a vertex have more than one normal in this case as well? Thanks pal, John From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Martz Sent: Wednesday, October 08, 2008 3:11 PM To: 'OpenSceneGraph Users' Subject: Re: [osg-users] Normal bindings and triangle strips Hi John -- I think normals with BIND_PER_PRIMITIVE on a N-triangle strip would mean you have N-2 normals. As we discussed previously, you'll use the OpenGL slow path (albeit stored in a display list) so the effective OpenGL calls would be: glVertex3f glVertex3f glNormal3f // normal for first triangle glVertex3f glNormal3f // normal for second triangle glVertex3f glNormal3f // normal for third triangle glVertex3f ...etc... This should result in a typical faceted appearance (with glShadeModel set to GL_FLAT). However, if you want smooth shading, you'll want to use BIND_PER_VERTEX of course. Which brings us to the next topic... I'm not sure why you are having problems with BIND_PER_VERTEX in a tri strip. It works just like BIND_PER_VERTEX with any other primitive type. Perhaps you could provide more information about the problem you're encountering. You say it works OK if the faces aren't radically different but I'm not sure why you'd use BIND_PER_VERTEX if you were not trying to get a smooth-shaded result. What type of surface are you trying to render, anyway? Do you encounter the same issue in a vanilla OpenGL app? Paul Martz Skew Matrix Software LLC http://www.skew-matrix.com http://www.skew-matrix.com/ +1 303 859 9466 From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Argentieri, John-P63223 Sent: Wednesday, October 08, 2008 12:34 PM To: [EMAIL PROTECTED] Subject: [osg-users] Normal bindings and triangle strips Greetings All, Is it possible to define a normal for every triangle without using primitive type TRIANGLES? For instance, if I am using TRIANGLE_STRIP, what is the effect of setting normals with BIND_PER_PRIMITIVE? And why does BIND_PER_VERTEX seem so wrong on a triangle strip? If the triangle strip faces are not radically different I guess it works ok. But it seems impossible to declare normal vectors precisely when using triangle strips. Am I missing something obvious? Thanks, John Argentieri Software Engineer GENERAL DYNAMICS C4 Systems [EMAIL PROTECTED] ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
Re: [osg-users] Normal bindings and triangle strips
Hi John -- BIND_PER_VERTEX is BIND_PER_VERTEX, just one normal for each vertex. To approximate a curved surface, apps typically average the facet normals from each facet that shares a vertex, and use that average normal as the normal for that vertex. I'm pretty sure the SmoothingVisitor does this for you. If I remember correctly, the OpenGL red book goes into some detail about why you would want normals per facet or per vertex, and how to compute normals at each vertex. -Paul _ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Argentieri, John-P63223 Sent: Wednesday, October 08, 2008 2:01 PM To: [EMAIL PROTECTED] Subject: Re: [osg-users] Normal bindings and triangle strips Paul, I'm just trying to learn how it works. If the way you've described it is in fact how I can give each triangle its own normal in a triangle strip, then I thank you my friend. I hope that this is how it works in OSG when using tri strip and bind per primitive. What about bind per vertex and tri strips? Can a vertex have more than one normal in this case as well? Thanks pal, John _ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Martz Sent: Wednesday, October 08, 2008 3:11 PM To: 'OpenSceneGraph Users' Subject: Re: [osg-users] Normal bindings and triangle strips Hi John -- I think normals with BIND_PER_PRIMITIVE on a N-triangle strip would mean you have N-2 normals. As we discussed previously, you'll use the OpenGL slow path (albeit stored in a display list) so the effective OpenGL calls would be: glVertex3f glVertex3f glNormal3f // normal for first triangle glVertex3f glNormal3f // normal for second triangle glVertex3f glNormal3f // normal for third triangle glVertex3f ...etc... This should result in a typical faceted appearance (with glShadeModel set to GL_FLAT). However, if you want smooth shading, you'll want to use BIND_PER_VERTEX of course. Which brings us to the next topic... I'm not sure why you are having problems with BIND_PER_VERTEX in a tri strip. It works just like BIND_PER_VERTEX with any other primitive type. Perhaps you could provide more information about the problem you're encountering. You say it works OK if the faces aren't radically different but I'm not sure why you'd use BIND_PER_VERTEX if you were not trying to get a smooth-shaded result. What type of surface are you trying to render, anyway? Do you encounter the same issue in a vanilla OpenGL app? Paul Martz Skew Matrix Software LLC http://www.skew-matrix.com http://www.skew-matrix.com/ +1 303 859 9466 _ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Argentieri, John-P63223 Sent: Wednesday, October 08, 2008 12:34 PM To: [EMAIL PROTECTED] Subject: [osg-users] Normal bindings and triangle strips Greetings All, Is it possible to define a normal for every triangle without using primitive type TRIANGLES? For instance, if I am using TRIANGLE_STRIP, what is the effect of setting normals with BIND_PER_PRIMITIVE? And why does BIND_PER_VERTEX seem so wrong on a triangle strip? If the triangle strip faces are not radically different I guess it works ok. But it seems impossible to declare normal vectors precisely when using triangle strips. Am I missing something obvious? Thanks, John Argentieri Software Engineer GENERAL DYNAMICS C4 Systems [EMAIL PROTECTED] ___ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
