A "unit sphere" is a sphere that is one unit in radius
(or diameter). Basically, Sphere(1.0f);
You can see exactly what's going on if you add your
geometry to a regular branchgroup and not a Background
object.
The mechanics are something like this. A sphere is
placed around the camera and the interior of it is
texture mapped. It is drawn first, with zbuffering
turned off. Zbuffering is then turned on and the rest
of the world is drawn. By the painter's algorithm,
the image on the sphere appears to be in the infinite
distance.
If you modify the BackgroundApp that comes with Sun's
tutorial to do what I said above, you can see the
stars gathered together in a small circle around the
origin.
--- Z H <[EMAIL PROTECTED]> wrote:
> Hi ,
>
> I know that an object is placed on the orign in the
> coordinates by default. but if I want to place a
> background image(2D) on the screen,
>
> 1>where will it be put in the coordinates by
> default?
> 2>can i move the background image in the
> coordinates?
> for example, I move it to the plane of (0,0, -20).
>
>
> another question, I read the sun's "Getting Started
> with Java3D API",it mentioned : the onlt tricky part
> is in the specification of a geomtric background.
> All
> background geometry is specified as points on a unit
> sphere."
>
> what does that mean? what is the unit sphere here?
>
> thanks in advance.
>
>
> Richard.
>
>
>
>
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