Z Buffer Problem in Client-Server
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
The classic Z buffer alias problem seems to occur when running in client-server mode under some conditions. By that I mean that odd-shaped pieces of the near surface will be replaced by far surfaces, at certain view angles.
Running paraview 2.4.4 pvserver and pvclient (with -rc) on the same workstation (Fedora Core 5, Pentium 4) produces the attached image serverGL.gif from the window displayed by the server. The image in the client is the same. The result is more dramatic when seen interactively - dozens of small dark patches (the far surface) will flicker on and off as the object is rotated. Over certain ranges of angles no problem at all is seen.
The same arrangement using Mesa 6.5.2 for both client and server produces the attached images serverMesa.gif and clientMesa.gif. Now, huge chunks in the center flicker during rotation. This shows an additional problem where the image is broken into streaks.
Using Mesa for the server and OpenGL for the client results in both showing images like clientMesa.gif. This was the situation where the problem was first seen except that the server was a remote 64-bit parallel system.
I downloaded a fresh copy of 2.4.4 to ensure I was not using any of our local modifications.
The Z buffer problem goes away when composite is off; when orthogonal projection is used; or when lines (such as the center of rotation crosshairs or orientation axes) are also being displayed.
The attached file zbexample.vtk used for these images is one piece of a large set of files in the pvd format that exhibits the same problem. I've done many checks, looking for duplicate triangles etc., and haven't found any problems.