Is it possible to make 2D drawings in Cartesian coordinate system?

Can 2D drawings be easily drawn in a cartesian coordinate system? (without the need for complex code and math parts)

Can you give a very simple example of drawing 2D lines and circles for SharpGL (Wpf C#)?

It’s certainly possible to use OpenGL for 2D. However, a dedicated 2D API typically offers some features which OpenGL doesn’t offer directly and require a non-trivial effort to implement. The most common such features are: wide lines (with joins and caps), Bézier curves, non-convex filled polygons, complex paths (which can have holes or self-intersection), text rendering. All of those can be implemented with OpenGL, but the learning curve is much steeper than for something like cairo.