HI Yefei, The OSG's makeLookAt() implements everything exactly the same as gluLookAt so OpenGL docs will be a good guide. The only difference you'll see if there is transpose between the two.
Robert. On Nov 30, 2007 12:23 AM, Yefei He <[EMAIL PROTECTED]> wrote: > Hi, Robert, > > I'm doing some object rotation and translation stuff on my own so I > looked at the OSG math code for inspiration. From what I read before > OSG uses post multiplication, meaning if I want to transform a vector I > need to do a V * M or, in OSG functions, M.preMult(V), where V is the > vector and M is the transformation matrix. This multiplication order seems > to be supported by how a translation matrix is created, by assigning the > translation values to the bottom row of the matrix. But, I got confused > when examining the method of setting the matrix by look at values. In > Matrix_implementation::makeLookAt(eye, center, up), it calculates the > forward, up and side vectors f, u, and s. I assume it used the OpenGL > convention of -z as the default forward direction and +y the default up > direction. Then, it sets the rotation matrix R as: > > s[0] u[0] -f[0] 0 > s[1] u[1] -f[1] 0 > s[2] u[2] -f[2] 0 > 0 0 0 1 > > But, with this matrix, if I apply it to the default forward vector F0 of > (0, 0, -1, 1) via post multiplication, i.e. doing an F0 * R, I get (s[0], > u[0], f[0], 1), instead of the correct value of the current forward vector > (f[0], f[1], f[2], 1). I need to do a pre multiplication or R * F0 to get > the correct value. > > Is my understanding of makeLookAt() wrong? Does the matrix generated > by makeLookAt() mean something else? Or, does OSG use a clever way of > setting translation in the post mult convention by rotation in the pre > mult convention, and always separating them out when applying the > transformation? Can some OSGers help me clear my head on this? Thanks! > > Best Regards, > > Yefei > > > > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
