rendering the overlapped geometry of objects

OpenGL OpenGL: Advanced Coding
1

Hello Everyone,
I have a requirement to render the result of two objects added together. For instance, if two spheres touch each other I want to only see the object formed by the intersection of the two spheres. I think some people call this “Mutual Exclusive” volume. Other objects include cones and cubes. I also need to view sphere #1 with the sphere #2 cut out of it. The origin of all of these are arbitrary.

Do any of you know how to render these objects?

Also, I tried to copy and paste some C code into a this message and I got an error stating that the parenthesis were not allowed in the text. Can anyone explain this?

Thanks,
Tim

2

You need CSG (Constructive Solid Geometry).

There are two ways to do it:

  1. Calculate the Intersection/Union/Difference of the two objects on your own. The result is a polyhedra which you only have to display.

  2. Calculate the Intersection/Union/Difference of the two objects with the help of OpenGL. The result is only present in the frame buffer.

For the 2nd I have a link for you: http://www.sgi.com/software/opengl/advanced97/notes/node11.html .

The 1st one is really hard to accomplish with all special cases. But it has a big advantage: The resulting model can be drawn very fast. The 2nd solution will calculate the result new for each frame which makes it slow.

I know, there is a demo with sourcecode out there, but I didn’t find it at the moment.

Keywords: CSG, Boolean Operations, Set Operations.

Kilam.