Re: LANG: cameras

Chris Marrin ([email protected])
Tue, 10 Oct 1995 11:08:08 -0700

On Oct 10, 5:52pm, Michael Pichler wrote:
> Subject: LANG: cameras
> I have two questions concerning cameras, which are somewhat
> hypothetical. Most (all?) scenes I have seen up to now either define
> no camera at all (where the browser should generate a "useful" view),
> or define a single camera (possibly in a Switch to select one out of a
> list) before any geometry.
>
>
> 1. What happens on multiple cameras? I mean a sequence of a camera,
> some geometry, another camera, further geometry. The spec says that
> cameras are affected by the current transformation.

The last one should win. WebSpace has the ability to handle multiple
cameras in a specially named Switch node:

DEF Cameras Switch {
whichChild 0
DEF Cam1 PerspectiveCamera { }
DEF Another_Camera PerspectiveCamera { }
}

This will cause the cameras to come up in WebSpace in a viewpoints menu
with the given names. Browsers that do not understand this hint will show
the Cam1 view.

>
> Does this mean a camera is essentially a Rotation by the negative
> angle and a Translation by the negative position and an adjustment of
> the height resp. height angle (orthogonal/perspective projection)?
> Further cameras will do it the same way?

Effectively but the implicit transforms are not propagated.

>
>
> 2. What happens when geometry is defined before the first camera? Does
> one manipulate the first (active) camera or may the browser transform
> the whole world coordinate system?

That's browser dependent. WebSpace manipulates the first camera.
Transformations before that camera affect its position.

-- 
chris marrin      Silicon      http://www.sgi.com/Products/WebFORCE/WebSpace
(415) 390-5367    Graphics     http://esality.sgi.com/employees/cmarrin_engr/
[email protected]   Inc.         


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 with one trifling exception, is composed of   others."   - John Andrew Holmes

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