Random Buildings
As of 05/2012, FlightGear has improved support for randomly placed buildings. Please note that this wiki article may be outdated, the latest information on random buildings can be found in: $FG_ROOT/Docs/README.materials .
At a functional level, there are three different size of buildings (small, medium, large), with slightly different constraints (small and medium buildings are never deeper than they are wide, small buildings may have pitched roofs). Various parameters can be set in the materials.xml file, such as the proportion of each building size, the texture file (which is shared across all buildings), and the range of sizes of each building. The actual buildings are then generated by FG itself directly as OSG primitives.
Obviously, this would be pointless if frame-rates were hit to the same extent as they are with a similar number of normal models. The good news is that on my system there is _no_ fps drop from the random buildings. I get the same frame-rate whether or not the random buildings are generated or not. The same applies whether or not I'm running with Rembrandt.
Of particular note - I get significantly better frame-rates with this rather than the urban shader.
For those interested, the technical background is as follows: - a Quadtree is used to ensure very fast culling of the buildings - based on the work that Tim Moore did for the forests. - a single 1024x1024 texture is used for all the buildings, minimizing the number of state changes on the GPU - all the buildings at the leaf of the quadtree are part of the same geometry, so the GPU can churn through it very quickly without having to change state.
There are still some bugs to be worked out before this can be pushed to git, but I'm hoping to get it checked in over the weekend.
If someone is interested in spending some time creating a better default texture, please get in touch.