Tessellated shapes

Hi all,
I did get no answers for my posts in beginner thread, due to that I post here:
The goal:

The tasks

  1. Create holes in red object
  2. Slice the red object where its cross section intersects with blue nearby surface.
    Red and blue shaepes are tessellated polygons.

In my opinion to fullfill these tasks I need to know whether the following techniques are applicable to Tessellation object.

  1. Is it possible to change the extrusion direction on tessellation applied shape ( kinda nested tessellations). If it’s possible that way I’ll cut holes. (probably feeding new gluNewTess2 object data from resulting/previous gluNewTess1 object )

  2. To get slicing effect: I should know whole vertex data of resulting tessellation shape and after that I may apply vertex projection on plane, 3D volume slice etc… but the key point is vertex data manipulation of resulting tessellation shape.

Any help will be appreciated so much cause I’m really stuck at that!


I’m afraid I don’t really understand what you are asking for (which may be because I don’t know much about CSG). For example, what is the extrusion direction that you want to change? As far as I know the gluTess* functions are meant to split complex planar polygons into planar convex non intersecting polygons (suitable for input to OpenGL), so I don’t see where extrusion is involved?

Anyway, I think part of what you want to do is record the output of one tessellation and use that during a second one. If that’s the case you need to register callbacks (using gluTessCallback) that instead of passing data to OpenGL (e.g. by calling glVertex) store that data into arrays (or possibly VBOs if you want to use it for rendering too).