A 3-D drawing in WPF involves four ingredients:
A viewport, which hosts your 3-D content
A 3-D object
A light source that illuminates part or all of your 3-D scene
A camera, which provides the vantage point from which you view the 3-D scene
Of course, more complex 3-D scenes will feature multiple objects and may include multiple light sources. (It's also possible to create a 3-D object that doesn't require a light source, if the 3-D object itself gives off light.) However, these basic ingredients provide a good starting point.
Compared to 2-D graphics, it's the second and third points that really make a difference. Programmers who are new to 3-D programming sometimes assume that 3-D libraries are just a simpler way to create ...