I have no idea how DirectX works and to be honest am not very interested in finding out. I like OpenGL. I am writing an engine/set of modules, part of which includes setting up cameras and lenses and all this fun aspect ratio stuff, but it won't be ready for consumption for some time yet.
There are some projection matrix modules floating about by other people which would cover most of the stuff you would want to do.
There are some projection matrix modules floating about by other people which would cover most of the stuff you would want to do.