Facade Tuning and Tips

I have updated some of the facade documentation on the wiki with new performance tips for using facades.

A few quick notes:

• Your facades must be counter-clockwise (when viewed from above). Do not repeat the first point; X-Plane will "close" your building for you. (A four sided building should have four points, not five.)
• If you turn off two-sided facade drawing and your walls look wrong (and your roof disappears) your facade is wound in the wrong direction.

The performance tips go into a fair amount of detail about saving memory. Most of X-Plane's rendering fall into two categories:

1. Shared meshes (objects), where the geometry of the object is saved once and used lots of times. Objects usually hurt frame-rate by consuming CPU time, because for each drawing of the object, we have to do some setup to draw that shared geometry in a different location. (Version ten should feature some major improvements in object efficiency.)
2. Non-shared meshes (everything else), where every single "instance" of a tree, facade, forest, etc. is uniquely constructed in memory. Non-shared messages are very fast (because we can submit a huge pile of non-shared messages to the video card in one shot) but they consume a lot of memory (because we pay for RAM per building/tree, not just once). Typically non-shared meshes are limited by virtual address space, not by framerate.

Facades are non-shared meshes, so the performance tips focus on how to limit the amount of RAM needed to represent your facade.