The basics of coordinate systems, graphics elements, and constructing and building BGL files are all covered in topics included in this SDK. The focus of this topic is a brief outline of file types and where to put the files once you've created them.
Four basic file types contain the scenery in Flight Simulator:
BGL files contain object and seed scenery design as well as navaids, communication, and other miscellaneous information.
Many BGL object commands use textures to fill in surface areas (for example, textured polygons). Texture files usually have the extension .r8, signifying rectangular, 8-bit texture. These files contain 256 x 256-pixel textures with 8-bit color, resulting in files that are 65,536 bytes long (64K). Although these files are usually called .r8 files, they can be called anything because the BGL command that uses them must specify the file name of the desired texture. Seeds use textures, as well. These 64K, 8-bit textures use the extensions .r8 (farm.r8), .0 (coast3.0), and .1 (coast3.1).
Designing scenery, control panels, and other elements using only 256-colors is a real challenge. Because scenery varies so widely from area to area, BGL was designed so the 256-colors could be changed from area to area; that is, each area can have a color palette that is appropriate to that area. The .pal file specifies what these colors are. Each .pal file consists of 256, 3-byte RGB triplets, resulting in a file size of 768 bytes.
As colored objects move into the distance, their colors must fade toward gray to create haze effects. The haze tables correspond to a .pal file and contain 16 haze colors that you can apply to "fade out" the 256 palette colors. Haze files are 4096 bytes long.
The following snapshot of the Flight Simulator directory structure illustrates where you should put your .bgl, .r8 , .pal, and .haz files.
FltSim5\Situation
Videos
Aircraft
Pilots
Scenery (.bgl files go here)
Panels
Textures (.r8, .pal, and .haz files go here)
Sound
By putting your scenery and texture files in the directories shown in the preceding example, you ensure that your files will be "seen" by the BGL graphics system and that your scenery will be displayed in Flight Simulator.