Scenery LOD ideas for FlightGear

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Revision as of 15:52, 13 February 2012 by Th3flyboy (Talk | contribs) (Ideas: added more comments regarding threading and CDLOD, along with Project Rembrandt.)

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Moving forum discussion to the wiki:

Ideas

Maybe there could be one single globe texture, and each tile btg would have it's correct texture coordinates into that image.

For LOD, I'd implement something like this :

  • Allocate a huge texture for a single 10x10 degrees area
  • load tiles as usual
  • render the tile to a small subpart of the huge texture
  • replace the tile geometry by a quad using the corners of the tile and map the small chunk of texture to it
  • unload the tile geometry to free memory
  • repeat for each tile of that area
  • save the texture to disk and repeat for another 10x10 degrees area

Sharing the same texture for a huge area save state changes. The tile quad geometry could be saved in the btg format to a Terrain.LowRes directory tree, using the material property to reference the shared texture


  • For the LOD algorithm, CDLOD [1] would probably be the best bet. CDLOD is like Chunked LOD, but plays nice with the GPU, and subdivides the LOD based on the distance from the camera/view point.
  • the LOD algorithm should be moved to a seperate thread, otherwise it really will just drain on the main thread, and will have less, if not worse performance that is possible with a properly implemented LOD system. This may have some problems however due to the potential for the LOD system to have issues with the property tree and threading.
  • It may be wise to base the LOD changes off of Rembrandt, rather than the current FGFS code base. Deferred rendering from Rembrandt is a major rendering change, and it may or may not play nice with a new LOD implementation based on the non-deferred rendering of the current code base.

References