VRML - visibility detection

Author

visibility detection

mdk

2004-04-21, 11:05 pm

Hello,

Is there any way to check if some object is really visible on the screen
(two options - in pure vrml97 or with Blaxxun Contact extensions)?

VisibilitySensor is unfortunately not enough:

"In other words, it is not OK for a browser to say that something is
invisible when it can be seen, but it is OK for a browser to say that
something is visible when it actually isn't." (from 'Annotated vrml manual')

TIA
md

Joerg Scheurich aka MUFTI

2004-04-21, 11:05 pm

> Is there any way to check if some object is really visible on the screen

The VisibilitySensor to not use a object, only a box, that approximates
the shape of a object.

And it do not detects "real" visibitity.
As far as i can see, it detect only if parts of the object are inside the
screen or not.
It do not detects, if there are other objects blocking the view to the box.

so long
MUFTI
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Holger Grahn

2004-04-21, 11:05 pm

"mdk" <removeit-mdk@gazeta.pl> schrieb im Newsbeitrag
news:c5um3p$2is$1@korweta.task.gda.pl...
> Hello,
>
> Is there any way to check if some object is really visible on the screen
> (two options - in pure vrml97 or with Blaxxun Contact extensions)?
in Bitmanagement Contact there is Occlusion Culling support
(requiring an OpenGL extension)
It can test how many pixels of an (invisible) bounding box are really
visble after
z-buffer testing.
It requires sorting of the scene (Oct Tree, QuadTree, BspTree) and tight
bounding box.

Another cheap aproximation could be done using ray-hit test between a point
towards point
on the object.

-- Holger

GiL_TheB

2004-04-21, 11:05 pm

> Another cheap aproximation could be done using ray-hit test between a point
> towards point
> on the object.

here is an example,
http://gil.theb.free.fr/protos/flare/flare.wrl