personal taste.

more unit tests for the quaternion to 3×3 matrix conversion.

mathematical writing, and add static constructors to create quaternions
from a rotation.

it's a bit less confusing.

code for all matrices.

needs to know about Direct3D headers etc.

the Scene code still breaks Direct3D rendering.

class, so that the calling code does not need to know what the backend is.

issues that were introduced with the Direct3D changes.

retrieve the constant's register index in the description table. This also
allows us to use a single uniform handle for both the vertex and pixel
shaders in a PS3 Cg program.

support is still missing.