What exactly does "clip space" mean?

[MelvinEng]

Hi all,

I find myself perpetually stumped by the term "clip space" mentioned at every turn in OGL literature. Whilst there is brief mention of the elements making up the projection matrix in both the red and blue books, there never was any attempt at explaining how these were derived. And without such foreknowledge, it becomes quite impossible to grasp what the term "clip space" actually means...(other than saying it is where vertex coords are clipped against -Wc and Wc, that is)
Can somebody kindly point me to relevant resources, references, websites etc?


Thousand thanks!

[Jambolo]

Vertices go though a series of transformations in order to determine where they are on the screen. The stages are generally:

model space
world space
camera space (aka view space and eye space)
clip space
screen space

The reason for the name "clip space" is that this is when view frustum clipping is done. At this point the view frustum is in the shape of a rectangular box (all sides parallel) and it is faster to clip against a box than a frustum.

[MelvinEng]

Well, actually I do know that part already(the books do explain how clipping is easier against a cuboid volume than a truncated pyramidal volume).
But what I don't get is *how* the projection matrix works to transform vertices from eye to clip space.
Basically I need to understand exactly what the projection matrix does in order to fully appreciate what "clip space" truly means...and especially why the clip coords of those verts inside the frustum will always be within -Wc and Wc.