   What could be wrong?
  I display a cylinder-shaped surface object in OpenGL. The code works perfectly in a PC. However, after we ported it to a Mac, the surface rendering fails like this:If I use lighting on both sides of the surface, only half of the outside of cylinder shows up correctly, and the other half appears like stripes; if lighting is on one side (with normals pointing to the inside of the surface), the inside of the surface shows up correctly.I'd been fighting with this for the past two days without success. What could be wrong?Thanks in advance.   
  Code please!   ;  Thanks MARS_999. Problems solved, and it's because the visual I chose didn't have depth buffer enabled. Never expected such a thing (depth buffer!) to happen.   