HI again,

I wonder if the thing I try is possible at all. The problem does not consist of moving an entity around (coupled to the mouse). My problem is not being able to move the entity just up to every border (reaching the border of the window (view) and not going beyond it).
I think - Dude - that you put up a crosshair or something to shoot at entities. So you use a normal mouse-pointer on your 2D screen and get a vector from the camera position in the direction you point with your mouse. Tracing along this vector you get the entity that is first hit. So you got the coordinates of that entity (or whatever obstacle).

For my 3D-pointer I think I need something like getting the dimensions of the "room" I can see in my view and align the maximum values to the maximum values of the 2D-screen-mouse-position (i.e. pointer.x, pointer.y).
Moreover I see problems in tilting or rolling the camera.
If someone has an idea how to do this ... I would be thankful if you share!