On Friday 23 February 2007, Robert Osfield wrote: > On 2/23/07, Paul Martz <[EMAIL PROTECTED]> wrote: > > Robert, please correct me if I'm wrong here. I'm just getting to writing the > > QSG section on matrices... > > You seem on track to me. > > OpenGL books do use M x v ordering vs. the OSG's v x M. > > OSG started off use post multiplication I guess because that's what we > were used to, we did discuss changing a number of years back but there > was non consensus on changing so we stuck with what we have. > > I do still wonder about changing it to be consistent with OpenGL books.
I think that Diggory meant the column-major vs. row-major convention of the matrices (OpenGL is column-major, OSG is row-major). This is indeed an easy trap for the unwary when one starts accessing the members of the osg::Matrix classes directly - you need to reverse everything and add a transposition here and there if you are rewriting code to use OSG. This could be a worthy addition to the documentation on the osg::Matrix class. Regarding the use of the pre/post-multiplication terms - Paul, please, be very explicit with what you mean in the book you are preparing. This is frequently the source of confusion in many books, I have seen somewhere an author say that "we post-multiply ..." and he multiplies M . v because the vector is *after* the matrix, instead of referring to the matrix as Robert does. I prefer to not use these terms at all and to write down the ordering explicitly instead in order to avoid any confusion when lecturing or speaking to somebody. Regards, Jan -- Jan Ciger GPG public key: http://www.keyserver.net/
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