A facade is a new special type of object in the X-Plane 8 scenery system. Normally an object is specified as an OBJ file and placed in the scenery at a point and given a heading. With a facade, a facade specification text file (.fac) specifies what texture should be used for the object and how to build flat walls from part of the texture. The facade object is then placed in the scenery file along a polygonal path, and a building is extruded.
Facades allow you to specify a large number of buildings, each with a different shape, using one texture. The facade object is built from your facade specification text file in a smart manner, with the texture being replicated as well as stretched to look good at different sizes.
A facade specification text file specifies how to build a facade object along a polygonal path. The facade text file specifies a texture; each facade object may (like OBJ files) use only one texture.
The DSF file will specify a polygonal path for the facade object and the number of floors to build; this lets each facade object be a different height.
A facade specification text file may designate a ring or chain facade. A ring facade object is a closed loop, which is useful for a building. A chain facade object is simply a set of connected links, which might be useful for a fence, etc.
A facade specification contains one or more levels of detail (LOD), or definitions for what the facade should look like at different distances. Each facade LOD specifies a minimum and maximum viewing distance. The various levels of detail must be continuous without gaps; the facade will not be drawn beyond the last level of detail. (This is the same as for OBJ files.)
Each LOD for a facade specification is in turn made up of one or more walls. Each wall is broken into a number of horizontal divisions called panels, and vertical divisions called floors. Each wall specifies its panels and floors in terms of the texture for the facade object, as well as a resolution for the texture, to convert from pixels to meters. As a wall in the facade object is stretched or shrunk, panels and floors are added and removed to make the wall the right size. Each floor and panel in a wall can be specified as repeatable or non-repeatable, for visual control of the wall.
Each wall has a minimum and maximum length; as a facade object is built, x-Plane will look through every wall definition and randomly pick one wall whose length range matches the wall being built inside the sim. This allows you to specify one wall for short building sides and one wall for long building sides.
The roof of a facade (if specified) is always a solid color and is specified as a coordinate on the facade's texture. Multiple roof coordinates can be provided, in which case X-Plane will pick one randomly.
The top floor of a facade can be sloped inward on a per-wall basis. Strange results may occur if the walls collide when angled.