Hardware Precision(NDC) question

OpenGL OpenGL: User Software
1

Hi,

I’ve question about this statement :
“In practice, the limitations of hardware precision can produce points having a normalized z-coordinate slightly greater than one. This causes severe problems when the z-coordinate is converted to an integer value to be used in the depth buffer because the stencil operations that depend on the depth test to render shadow volumes may no longer function correctly.”

Source http://www.gamasutra.com/features/20021011/lengyel_pfv.htm

Can anybody explain to me about that hardware limitation which cause NDC slightly greater than one ?

Thanks.

2

Originally posted by EonStrife:

Can anybody explain to me about that hardware limitation which cause NDC slightly greater than one ?

Accumulated IEEE floating point math rounding errors.

3

oh, thanks for the clue. While google-ing I got this site :
http://support.microsoft.com/kb/q42980/