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Claudiu Mihail's blog

Change of plans


07:04:37 pm Permalink Change of plans   English (US)

Categories: GSoC 2010, 358 words I've been trying the past few days to get some headway on the occlusion culling. After resorting to drawing the meshes quicker with a variant of the DrawMesh method (available in the OpenGl plugin), I have tried several schemes involving bounding boxes in order to reduce the query overhead. Unfortunately all of the methods I have tried have all sorts of corner cases where the culling scheme either culls geometry incorrectly or it is extremely conservative, culling far to little. The methods that have cases where geometry is culled incorrectly aren't well suited for a general culler. The ones which are too conservative aren't very good because they don't really do very efficient work.

So...what to do? Well, as far as I can see, with the midterm deadline approaching, there's only one sure way to get some results which are to focus on implementing a mesh simplification algorithm. This has several advantages:

1) There already exists a basic implementation, written by my mentor with the CHC++ algorithm in mind. The main problem with it is the overhead created by rendering the same geometry twice. By rendering simplified, but accurate, meshes for occlusion queries the overhead will be eliminated enough to make using the CHC++ algorithm practical.

2) The mesh simplification scheme will enable the new culler to work for generalized models and scenes.

So which algorithm to use? Well, there has been numerous research related to the topic of mesh simplification. I've been doing some research today and the algorithm that seems most promising in terms of speed, accuracy and generality is Garland and Heckbert, which uses a quadric based polygonal surface simplification scheme. There's very little time left until the midterm evaluation and I hope to have this algorithm functioning by the 11th of July. Once that's done I can integrate it into the the CHC framework.

I'm cutting it close on time as far as midterm evaluations are concerned, but I hope I'll have some concrete results come the mid-deadline. I'll provide some updates as I progress into the implementation of the mesh simplification algorithm.


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