What is normal plane ?

Can someoane tell me what is normal plane ?

I wouldn’t know.

But maybe you mean “plane normal”?
That would be a vector of length 1, pointing “up” from the plane.

Something like this:

  / |
 |  |
 | ----->
 |  |
 |  /
 | /

I’ve drawn the arrow from the plane’s surface but it’s only a vector, a direction. It’s not a line with two endpoints.

No ,is not a plane nomal.It’a a term I found in the glut 3 specification , I quote :

"Normal plane The default frame buffer layer where GLUT window state resides; as opposed to the overlay."

I simply can’t understand this definition.
I know what a frame buffer is -I think-(a collection of pictures stored in video board memory for being displaid),but I can’t understand how can a frame buffer relate to layers ?The notion of layer is associated in my mind with Macromedia Flash’s or Photoshop layer …

Could you try and explain me the definition (and the one below also)?
Or point me to some free books on opengl and glut.
I know I’m asking too much , but I promised an uncle of mine to do a furniture design program for his workshop in a month , and I’m kind of desperate.

“Overlay A frame buffer layer that can be displayed preferentially to the normal plane and supports transparency to display through to the normal plane. Overlays are useful for rubber-banding effects, text annotation,
and other operations, to avoid damaging the normal plane frame buffer state. Overlays require hardware support not present on all systems.”

OK, I see. I figured it might have been a language issue. Sorry about that.

I haven’t used GLUT, but I get the impression that what is meant by the normal plane is sort of the “background scene”.
It seems to be basically the frame buffer before any overlays are rendered on top of it.
And overlays can replace all or part of the frame buffer.

Overlays seem useful for drawing “rubber bands” and coordinate axes in editors, or maybe even a HUD (heads-up-display).
My guess is that it might allow you to avoid redrawing the entire scene if the overlay is the only thing that changes.