Stationary Objects (wasRe: Billboard Objects?)

J D Wood ([email protected])
Thu, 7 Dec 1995 14:19:48 +0000


On Dec 5, 8:04am, Mitra wrote:
> Subject: Re: Billboard Objects?
> I'd like to suggest that the way to do Billboard objects is not to focus on
> the thing being displayed, but on the transform. If we defined something
> like
>
> CameraTransform {
> isA Transform
> fields [ SFBITMASK axis ]
> axis X|Y|Z # Specifies which axis to always
> rotate to face the camera.
> }
>
> Note - that "rotate to face the camera" means to rotate so that the local
> coordinate space of the object, matches that of the camera.

I work in the aesa of visualization and have been using VRML as a way of
sending results
from the visualization process across the WWW. This requires information about
the visualization
process to be sent with it such as values used in the viz process and colour
legends to allow
the mapping of colour back to values. It is very important for this information
to be viewed
alongside the object and for it not to move when the user changes camera
position.

I am currently using a 'feature' of Inventor which is unspecified in the
current VRML spec which
I described in an earlier posting ('Static objects in VRML Scenes' but which
received little attention).

This feature wouldn't be especially computationally expensive to implement,
having rendered the stationary
bits once, they could simply be rendered on top each frame update. This feature
is important for
the scientific vizualization community and I feel that to ignore it would mean
we would have to cesate
non standard VRML scenes and distribute our own browser to be able to view it
correctly. This is not at
all in the spirit of VRML and not a road I wish to go down.

I would propose extending the above node to allow the original rendering of the
objects beneath it
(yes objects, its not just text) to remain constant after any subsequent camera
change.

-- 
jason
--
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