As of 05/2012, FlightGear support "random buildings", which are generated at runtime and placed in Urban and Town areas. In v2.8.0 these take up a lot of memory, but in subsequent releases this has been improved significantly.
Building generation is configurable through materials.xml, and documented in $FG_ROOT/Docs/README.materials . It is designed to be flexible enough that we can have different types of cities in Europe compared with the USA, or Africa. The current texture used for the buildings is a proof of concept, and rather limited by Stuart's artistic abilities. If anyone is interested in creating a better texture, please get in touch with Stuart on the mailing list or forums.
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.
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
- AutoGen Scenery for FlightGear