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VBlimits

Tri List or Strip/Fans

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what is faster with todays HW?? a Tri Indexs List or strips and Fans?? Thanks -VBLimits Sorry about the Spelling..

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Depends on your data.

Minimising API calls is a good thing to do.

Fans often result in a lot of API calls because you get one fan per call (unless you have a way of specifying a new fan centre point in your data stream to be able to do more than one fan per call). [hardware manufacturers like nVidia say that less than 200 polygons per API call will hurt performance]

Indexed Strips get you the lowest vertices per polygon count, but you need to have long strips to avoid the API call cost. Degenerate triangles can help a lot here for turning corners etc.

Another key to getting best vertex throughput is making the most of the vertex cache. It only works with indexed data (which is why its the indexed variety of strips which are particularly good).

If you''re trying to do deformable geometry or other dynamic changes to the topology such as VIPM, strips can be a pain, and in cases impossible to modify without re-stripifying.

Well constructed triangle lists get around 1.5 to 2 vertices per polygon, which isn''t as good as a long indexed strip, but they are more flexible for dynamic update.

So in performance order:

1) If you don''t need easily modifyable topology, have a good stripifier which generates long strips (with possible use of degenerates) and are able to share indices suitably (in a vertex cache friendly way), strips get you the highest vertex throughput.

2) If your indexing and vertex layout is cache friendly and you don''t have too many attribute discontinuities, indexed lists get good vertex throughput. In models where the stripifier fails to make a few long strips, indexed vertex lists can get higher throughput.

...

99) Unless you''re making 200 polygon cones or circles or have some way of specifying multiple fan centres, fans cost you tons of API call overhead - not good.

--
Simon O''''Connor
Creative Asylum Ltd
www.creative-asylum.com

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Thanks that what i needed to know
but now i have one more Q
how would i go about making a "Stripafier"??

i know that is a big Q but if you can just point me to a Articel or somthing that would bee good to thanks



-VBLimits
Sorry about the Spelling..

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Amongst others:

1. STRIPE: http://www.cs.sunysb.edu/~stripe/

2. www.nvidia.com/developer has one which''ll generate D3D and OpenGL suitable strips which are optimal for nVidia vertex cache sizes.

3: http://home.earthlink.net/~mmchow/strips/strips.html

--
Simon O''''Connor
Creative Asylum Ltd
www.creative-asylum.com

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