Resources for 2D Level Editing Program

I'm developing a 2D game, and I've just started working on the level editor. Levels will be defined as a list of 2D polygon shapes.

The level editor should allow creating of custom polygons defined by clicking the mouse at points, and translating, scaling and rotating the polygons. The functions will be like the functions in photoshop i.e handles on objects.

What I am looking for is resources on how the programming for an application like this is done. Preferably I'd like the source code for a demo (I was looking at the source code for the SVG editor Inkscape but it's far too complicated for my needs).

My working language is C#, so I would prefer sourc开发者_C百科e code in that language.

Would someone be able to point me in the right direction?