I'm implementing a simple project for bidimensional shapes's drawing using opengl.
I already implemented a little engine for manage vbo buffers ,camera and shaders.
The 3d scene is incapsulated in a qtGLWidget of qt 4.8.
Now i would create the drawing of a point, a line ,a polyline and some circles,
1)what are the better rapresentation methods of these entities?a parametrics rapresentation?
2)i would implement a mouse 3d picking and i saw a demo for this, but was used a bounding box system for this(with a bounding sphere), there aren't more accurate system? or is sufficent change the bounding sphere in an axis oriented bounding box?
3)how i can implement a box selector? with the drawing of a rectangle from the start point clicked , to the current mouse position,without Flipping with a shader?

There is a good demo or tutorial

I use opengl 3.2