OpenGL, Wireframe and Clipping Planes

Discussion created by Th3M4dH4tt3r on Apr 16, 2010


I develop a preoperative planning software for a medical company, and I found a problem with ATI Radeon cards concerning OpenGL clipping of wireframe drawn meshes (through glPolygonMode set to GL_LINES).

On NVIDIA cards the meshes are correctly cut, achieving automatically the new vertices (intersections with the cutting plane) that are consequently connected to maintain a convex polygonal mesh.

On ATI cards, instead, even if the meshes are correctly cut, they are not closed, due to:

a) the lack of generation of the intersection vertices (and following edge lines)


b) the setting of those lines as not boundary (glEdgeFlag set to FALSE)

In both the cases the clipping would not respect the specifications of OpenGL.

If you need I can post images to show the fact I'm talking about.

The automatic clipped mesh closing is a vital feature for the medical software I work upon. May you release a patch in the next driver update or tell me if there's a command/procedure to re-enable the edge lines generation during clipping?

Thank you in advance.