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quick question re: shadows

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i think that depends on the situation...i think shadow maps are not getting much slower as the triangle count of the shadow casters increase, but you need 1pass per light...Shadow Volumes get much slower with highpoly meshes i think(because finding the silhouette will be much slower).

Somebody correct me plz if i'm wrong


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Depends on a lot of things...

Hardware, native support for shadow maps, special stencil operations to make shadow volumes faster, scene characteristics, etc, etc, etc

Some hardware (i.e. NVidia) has special settings that duplicate(maybe even quadruple) the rendering throughput when rendering to a shadow map. There is also hardware (from both NVidia and ATI I believe) which has support for double sided stencil, which makes shadow volume rendering faster.

Sometimes speed does not matter as much, if you are working on a fighting game, you can have beautiful shadow volumes for both characters, but it is very unlikely that you can afford shadow volumes on large scenes.

Note also that it is easier to get soft shadows with shadow maps than with shadow volumes.

There has been endless debates about which technique is better, and IMHO it really depends on what you are trying to achieve. Shadow volumes can eat your fill rate really fast, leaving very little room for doing other effects (i.e. post processing effects), but this is fine if you are not computing them for a lot of objects. Shadow maps are easy to understand and implement, but you do not get the nice hard shadows you can get with shadow volumes. On the flip side you can implement nice soft shadows easier with shadow maps than with shadow volumes.

My 2 cents, Hope this helps

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One of my collegues has published an article about shadowmaps on the GPU (fast and very smooth)...
take a look - "Multiple-Depth Shadow Map"


EDIT: Clickified for you -- VertexNormal

[Edited by - VertexNormal on July 26, 2005 8:45:26 PM]

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I've searched for "Multiple-Depth Shadow Map" and found the paper in this link...
If you want to contact the authors

Christian Azambuja Pagot
João Luiz Dihl Comba
Manuel Menezes de Oliveira Neto
Instituto de Informática - UFRGS
{capagot, comba, oliveira}

send an e-mail to the first one, I belive he can give you the paper

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