How is culling done

OpenGL OpenGL: Basic Coding
1

Hi,

I am using Flightgear software package.
I want to know how is culling done basically.

Regards
Hemalatha

2

There are a number of ways to do it, one for example is to calculate a bounding box for your objects and then do an intersection test to see if that bounding box intersects the view frustum, a simple cheating is to calculate abounding box around the view frustum and use that to do the intersection, this is simpler but will not cull everything outside the frustum of course.

I remember that there are a least a few tutorials on this using OpenGL so you should be able to find it with google.

Mikael

3

Hi Everybody,
Thanks for promt reply.

I am using FlightGear 0.9.4 Simulation Software.

We are reading a data file which is in binary format(*.btg) and adding every object
in scene graph(Tree structure).
Now our scene graph contains all the objects which will be used further for culling
and rendering
Object contained in the scene graph are: modal branch, aircraft branch , terrain branch
and different lightening.

We are using frustum culling technique . In constuctor we are setting the frustum values
Ortho=false;
nnear=SG_one
ffar=1000000.0f
hfv=SG_45
vfov=SG_45

I have lot of doubts………

  1. How are we setting the frustums six plane and where (are we placing in the scene
    graph)
  2. How are we selecting part of the objects from scene graph and placing it in frustum
    Which is being used for further culling and rendering.
  3. A concept called extend sphere over sphere is used. I didn’t get the concept.

If any one knows about culling and rendering plz explain me in detail .