Selection by polygon

OpenGL OpenGL: Basic Coding
1

I’m trying to find a way to get the objects under given polygon.
Which means, that the user will draw a polygon on the screen and i will give him all the drawn objects under this area.

  1. I know that we can use the picking method but this is for point or rectangle…
  2. I thought maybe, if there is a way to clip the viewing volume by given polygon, and then draw the scene in selection mode in the cut viewing volume… but i couldn’t find this clipping option… if there is.

Thanks.

2

In addition,
I know that intersection checks between the user polygon to all the others object is an option,
but the drawing objects are complicated and changed every zoom, so i prefer to skip this calculation and if there is an option to use like the picking method for a given polygon i would be glad.

Thanks again