From Mathias Froehlich, "This is a generic optimization that does not depend on any cpu or instruction

set.

The optimization is based on the observation that matrix matrix multiplication

with a dense matrix 4x4 is 4^{3 Operations whereas multiplication with a
transform, or scale matrix is only 4}2 operations. Which is a gain of a

*FACTOR*4* for these special cases.

The change implements these special cases, provides a unit test for these

implementation and converts uses of the expensiver dense matrix matrix

routine with the specialized versions.

Depending on the transform nodes in the scenegraph this change gives a

noticable improovement.

For example the osgforest code using the MatrixTransform? is about 20% slower

than the same codepath using the PositionAttitudeTransform? instead of the

MatrixTransform? with this patch applied.

If I remember right, the sse type optimizations did *not* provide a factor 4

improovement. Also these changes are totally independent of any cpu or

instruction set architecture. So I would prefer to have this current kind of

change instead of some hand coded and cpu dependent assembly stuff. If we

need that hand tuned stuff, these can go on top of this changes which must

provide than hand optimized additional variants for the specialized versions

to give a even better result in the end.

An other change included here is a change to rotation matrix from quaterion

code. There is a sqrt call which couold be optimized away. Since we divide in

effect by sqrt(length)*sqrt(length) which is just length ...

"