Re: [plib-users] XGL

[Steve B. <sjb...@ai...>]

Devrim Erdem wrote:
>
> VRML had the same problem and they have solved it by introducing wgz
> which is simply wrl+gz.

It didn't 'solve' the problem - it was a mere bandaid for a gushing wound.

The XGL web site contains a file for two green cubes.  It's 250 lines
of text - and 5Kbytes.

AC3D (which has another ASCII format) takes just over 1Kbytes for the
same thing. VRML takes 1.7Kbytes *WITHOUT* using the 'cube' primitive
(which would be cheating).  Those files compress down to 320 and 520
bytes respectively. The XGL file compresses down to 630 bytes.

It's even worse than that in fact.  The two cubes XGL file has very
nice 'round number' vertex coordinates, colours, etc.  If this was
truly arbitary geometry, the numbers would need many more digits
to specify them - the file size would be much larger - and would compress
much less efficiently.  When I tested two cubes in VRML and AC3D, I
deliberately used non-exact vertex coordinates in order to get a more
realistic test.

The SSG (binary) file for the same thing is 266 bytes...including texture
coordinates, per-vertex normals and colours - which were absent from the
XGL, AC3D and VRML versions.

Tuxkart (for example) has 1.3 Mb of AC3D files.  If I used XGL, (presuming
that the cubes example is typical) that would extend to perhaps 10Mb!
If I switched to SSG, I could get it down to about 0.2Mb.

People do happily download 2Mb OpenSource games.  They think twice about
downloading 11Mb games.

> The only thing that might be interesting is that there are other scene
> graph APIs around and wouldn't it be nice if all of these APIs build
> loaders for XGL instead or VRML, 3DS etc. Every API has a group of
> people trying to build loaders. Most of these loaders have problems.
> Most of the file formats are simply not good enough for realtime 3d.

It's my view that we first need to produce a standard scene graph API.

Until that is done, there is no prospect of having a standard 3D file
format - or even a very great degree or interoperability between file
formats and API's.

-- 
Steve Baker   HomeEmail: <sjb...@ai...>
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