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Submitted by , posted on 19 March 2003
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Image Description, by
This is a shot demonstrating the automated level-of-detail reduction on
arbitrary meshes in OGRE. I haven't submitted
an IOTD in a long time, but I thought it was about time: I skipped
submitting images of our terrain engine plugin(s), because people have seen
enough of those I think :)
The automatic mesh reduction algorithm takes account of the curvature of the
surface, manifold edges and seams in textures and vertex colours in order to
work out the 'least cost' way to reduce the mesh (which it does by
collapsing vertices onto each other). You'll see from the images above that
flatter areas are simplified more than angular areas, and borders (like the
edges of the eyes) are maintained in order to retain the general shape of
flat model sections. The result is that if these lower LOD meshes were
displayed in the distance, you can barely tell the difference between this
and the original model. Broadly speaking the algorithm is along the lines of
Garland and Heckbert (SIGGRAPH 97), with some extensions to avoid collapsing
manifold edges.
OGRE automatically uses the appropriate LOD mesh at runtime; the distance at
which this happens is is largely determined when you generate the LODs, but
you can also bias the decision per object and per camera, in order to weight
the results appropriately.
If you don't like the automatic LODs, OGRE also allows you to assign manual
LODs, including alternative skeletons for animated objects, if you wish.
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