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Do00d

A Question on Quadtrees relating to distance and hidden objects

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Do00d    122
well i was thinking of finnaly diving into the world of terrains and was gonna start making a simple multi texed terrain using a quadtree for culling however what happens if i view my terrain from one of the edges thus basically if it were flat i could see most of it the terrain would die on me then how do some of u ppl handle this? just get rid of the most distant parts? have some kind of occulsion with hills being able to hide other parts of the terrain>? plz help

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invective    118
1) Use fogging along with a closer in far clipping plane.
2) Use level of detail so far away objects (chunks of terrain in your case) are rendered with less polys.

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Do00d    122
hehe thanx anyway but i wa slooking for a more in-deapth response
doesnt the vert data stillg et sent to the card through using normal opengl clipping
thus not helping performance
also i dont wanna use lod
and in this case where u can practically see the whole terrain i dont think lod will help much

looks like ill have to do distance equations for the quadtree
oh well

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Sof    122
invective was totally correct, also a quadtree is perfect for doing Frustum (sp?) culling since it is already hierarchically organized. Also don''t dismiss the LOD, to me that seems the whole point of using a quadtree structure. In the case you mentioned the LOD would work great, if it is mostly flat the LOD can take advantage of this. LOD can work on the detail needed, not just distance is taken into account but the lumpiness of the terrain as well if you like.

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TerranFury    142
Note that without occlusion culling you''ll be doing just as much work - or probably more - when viewing a mountain range than viewing a flat surface. This is because of overdraw.

In general, you just have to deal with it. Occlusion culling for terrain is rare in hardware-accelerated implimentations.

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Bad Monkey    145
i believe zedzeek uses octrees and a PVS for his terrain in Gotterdammerung (hope i spelt it right that time )

an octree is not that much harder than a quadtree to implement, and you can reduce drawing quite a bit if your terrain is mountainous.

i would assume that to use an octree for occlusion culling, you could test to see whether a node blocks line of sight to another based on ray-terrain intersection calculations... which is essentially calculating a PVS... damn i hate it when i think in circles

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