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Virtual Worlds are described in Ascii files in an XML-like format,
with the extension .vre (eg.
Rendezvous.vre,
tarots.vre,
mythology.vre,
dax.vre,...).
Each line describes a VREng object according to the following format:
- Object type, <type like wall, web, gate,... announces
the type of the current object. The type is followed by one or
more attributes and terminated by a />.
- Object attributes, according to the attribute="values" form
- its name: name="given_name",
- its position in the space: pos="x,y,z,az,ax",
- its geometry: <solid shape="shape" dimensions materials textures drawstyle"
- shapes are line, rect, box, bbox, sphere, torus, cone, disk, point,...,
- dimensions are width, height, depth, radius,...,
- material lightings are
diffuse, ambient, specular, emission, shininess,
- textures on each face (in x and/or y and/or z),
defined as URL to a Gif/Png/Ppm/Pgm/Bmp/Tga/Jpg file
on an HTTP server somewhere on the Web,
(currently http://vreng.enst.fr/{gif,png,ppm,pgm,jpg,bmp,tga}/).
- its specific attributes: channel, specific values
- channel has the form of channel="address/port/ttl"
- attribute has the form of attribute="value"
Each virtual world is bound to a IP Multicast group address, one per world.
For the moment these IP multicast addresses are not dynamically allocated,
because, at this time, we have not found any mechanism (except SAP/SDP)
to allocate these addresses. These addresses are statically defined
in the configuration file in the range 224.255.0.0/16).
A server of IP multicast addresses named VACS (Vreng Addresses Cache Server)
is sollicited each time a world is called maintaining the uniqueness of addresses.
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