> Date: Thu, 30 Nov 2000 17:19:56 -0500
> From: Shawn Kendall <[EMAIL PROTECTED]>
>
> I have a quick question about Compress Geometry. In know that the
> memory/file footprint is reduce when using CompressedGoemetry.
>
> The question I have is, what is the performance effect? Does it increase
> performance, because there is less to process, or does it reduce performance
> because it has to do more work converting the compress data to regular
> floats/doubles? Or neither? :-)
Since compressed geometry is directly supported by Java 3D as a node component,
it's a very efficient way to store geometry in binary form and load it into a
scene graph.
However, the geometry must still be decompressed entirely into system memory
before it can be rendered; the software decompression process is too slow to
decompress each frame on the fly. (It's about 10X slower to do it that way).
Currently there is only 1 graphics accelerator in the world (rev. 2 of the Sun
Elite 3D) that can decompress geometry in hardware and render it faster than
uncompressed geometry. So at this stage in the development and deployment of
the compression technology there are no memory reduction advantages unless
you're using the latest rev of the Elite 3D.
The overhead of decompression is still usually much less than the overhead of
reading, parsing, and converting something like an ASCII .obj file into scene
graph components (e.g., on my machine, a 1.7MB .obj file takes close to 40
seconds to load and display, while loading and displaying the same model
compressed to a 450KB .cg file takes about 9 seconds).
So for now the main advantages to using compressed geometry are smaller file
sizes and transmission times, and faster loading. In the future more Sun
graphics devices (and hopefully other vendors too if the compression
technologly gets adopted) will be able to render compressed geometry directly,
so that geometry can always be represented in the scene graph in compressed
form.
-- Mark Hood
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