Is the Z axis positive or negative "into the screen"?

Hello forum again,

Another simple question for you all - is the Z axis positive or negative “into the screen”?

I’ve seen one tutorial where it’s negative. If this is true, why does glfrustum take only positive values for near and far planes, as if it is only concerned with POSITIVE values of Z ?

Thanks in advance,

BBJ

EYE-SPACE -Z is into the screen. glFrustum/gluPerspective takes positive values for near and far, which equate to Z=-near and Z=-far (in EYE-SPACE).