well, if you see something, then it "work better"
i think we have the same problem.

so, i think the gemglcleardeph and gemglclear does not only clear depth
buffer, but also the color buffer.
but i don't really see why, and how to solve this.

It works on both Nvidia and ATI on OSX, but not ATI on Windows. The code only clears the depth buffer, so I can't see what would trigger the clearing of any other buffers. Maybe the GLdefine constants are wrong or there is an OR being done? Try printing out GL_DEPTH_BUFFER_BIT, GL_CURRENT_BIT and GL_COLOR_BUFFER_BIT to the console.

cgc