History: SoC2013 Progressive Mesh Improvements

Source of version: 7 (current)

!Tasks
# __Compress LOD levels:__ I had an idea to compress LOD by up to 50% without performance degradation! My idea is to merge 2 index buffers into a single merged index buffer. The merged index buffer would consist of 3 parts. Let’s say we merge LOD1 + LOD2, then the beginning of the buffer would LOD1 faces only, second part would be LOD1+LOD2 shared faces and the third part would be LOD2 only. Imagine it as a frame shifting mechanism, where I just change the offset and size of the buffer instead of swapping buffer. (1 weeks of work)%%%{IMG(src="http://sajty.elementfx.com/gsoc2013/CompressedLOD.png",link="http://sajty.elementfx.com/gsoc2013/CompressedLOD.png")}{IMG}
# __Take into account vertex normals:__ This one is the most visible artifact in the output currently. Try out the MeshLod sample and check the color above the mouth while you reduce Sinbad.mesh. At 50% its dark, 52% its bright, 57% its dark. This is caused by self-shadowing. Fixing this would improve the quality of the output. (3 weeks of work)%%%{IMG(src="http://sajty.elementfx.com/gsoc2013/SelfShadowingLOD.png",link="http://sajty.elementfx.com/gsoc2013/SelfShadowingLOD.png")}{IMG}
# __Allow to profile LOD weights:__ Sometimes the generated LOD with high reduction looks nice…except just a single vertex which messes up the whole mesh. This may be a bug in the algorithm. In that case you need to reduce fewer vertices? Well what if you could just fix that single vertex. The idea is to create a small sample in the SampleBrowser where the artist can select (or step by step reduce each) vertex and change the weight of it manually. This also helps debugging progressive mesh algorithm. (2 weeks of work)
# __Weighted outer wall:__ This would be an optional feature and it may not be related to all kind of meshes. When I have made a visual benchmarking system for LOD in worldforge, we have noticed, that buildings are reduced less than other models. This is caused by the fact, that the wall has two sides and there are static objects inside the building. The algorithm currently doesn’t care on what is visible from outside and what not. The idea is to detect the outer wall of the reduced mesh in a pass before processing the progressive mesh algorithm. Also You can set the strength in the range 0-1 on how much should this influence the output (0=off;1=keep outer wall only) This would drastically increase efficiency of meshes which has internal faces like buildings. I couldn't find an algorithm for this problem, but I have planned my own algorithm and I would like to implement it. (4 weeks of work)%%%{IMG(src="http://sajty.elementfx.com/gsoc2013/OuterWall.png",link="http://sajty.elementfx.com/gsoc2013/OuterWall.png")}{IMG}
# __Allow to mix automatic and manual LOD:__ The idea is that you can reduce LOD1 by 50%, for LOD2 you use a manual mesh and for LOD3 you reduce the manual mesh by 50%. So it would make a hierarchy of LOD levels, which allows mixing automatic and manual mesh LOD levels. (1 weeks of work)
# __Create effective manual mesh:__ The idea is that you can use your favorite editor (like Blender) and restructure faces and remove vertices there, but you should not create new vertex positions! Then with a tool (maybe OgreMeshUpgrader or MeshMagick) you can bake it into the mesh as index buffer only LOD. (2 weeks of work)

!Schedule
* __Now - June 17: Community Bonding period__%%%
** Created prototype of outer wall detection algorithm: [https://bitbucket.org/sajty/ogre/commits/76e39d7f7a2d088f08046dd7ec131c66a64b4a2e|code]
** Created document explaining the algorithm: [http://sajty.elementfx.com/gsoc2013/OutsideDetection.pdf|document]
* __June 17: Coding starts __
* __June 17 – June 24: Compress LOD levels (1 week)__%%%
** Test: changing offset and size of the index buffer
** Bugfix: The mesh serializer is not saving the offset, so serializing Lod is disabled for now.
** Feature: LODs can be compressed. It is enabled by default, but you can turn it off.
** TODO: Fix mesh serializer.
* __June 24-July 15: Take into account vertex normals (3 weeks)__%%%This needs 3 weeks, because it also needs some experimenting, because there are multiple solutions. I could just compare the dot product from source to destination, but it may look better if I count the overall angle of the vertex before and after the reduction.
* __July 15 - July 29: Allow to profile LOD weights (2 weeks)__%%%Create ProgressiveMeshGenerator::setProfileData, where you can pass the custom weights based on vertex position. Creating a sample with an interface for profiling LOD and allow to export the mesh with the MeshSerializer.
* __July 29-August 5: Catch up delays or holiday (1 week)__%%%NOTE: I may go later on holiday and I may already start next task before Mid.
* __August 2: Mid Term Evaluation__%%%At this point I should be ready with first 3 tasks.
* __August 5-August 26: Weighted outer wall (2 weeks)__%%%This will be an optional pass before progressive mesh. It will be in a separated class. The goal is to calculate convex hull and do the appropriate calculations on the data. However before coding starts, I want to create a prototype of this, so that I can prepare for issues and make the schedule more stable.
* __August 26-September 9: Weighted outer wall improvements (2 weeks)__%%%I will implement an optional feature to use few ray traces to improve approximation quality, but I will decide this based on the results and current progress/delays. I may find other ideas at that date to improve it.
* __September 9-September 16: Allow to mix automatic and manual LOD. (1 week)__%%%This needs some Core changes in the LOD handling.
* __September 16: Soft pencils down __
* __September 16-September 23: Clean code, improve documentation. (1 week)__
* __September 23: Firm pencils down __
* __September 23-October 7: Create effective manual mesh (2 weeks)__%%%This will be an after GSoC task for completeness. This is not related to the core, but to the tools.
History: SoC2013 Progressive Mesh Improvements

Source of version: 7 (current)

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