DXTBmp - 16/32 bit Texture Formats in Flight Simulator and CFS2
FS2000 introduced several new texture formats for Aircraft and Objects. Expanding on the 8 bit Extended Bitmap format introduced in CFS it added the increased colour depth of 16 bit (65536 colours) and larger texture sizes (up to 1024x1024 and also non-square). These 16 bit textures came in 2 main variations - 4444 (4 bit transparency) and pure 565 for normal textures for textures requiring an Alpha channel(mainly Clouds but also used for some objects requiring transparent parts).
The Beta version of CFS2 introduced another format - 5551 (1 bit Transparency) which is not supported by FS2000.
The Release version of CFS2 replaced the 565 and 5551 formats with a new compressed format. Instead of four 565 "Normal" and four 5551 "Damage" 512x512 textures for each of the main Aircraft it uses one DXT Opaque "Normal" and one DXT Opaque+Alpha "Damage" 1024x1024 texture for each Aircraft. Because these are compressed they are each the same filesize as just one of the old 512x512 textures giving a saving of several megabytes for each Aircraft.
CFS2 also supports another new format - DXT3. This doesn`t seem to be used in any standard textures but will work. DXT3 is a combination of DXT1 with a 4 bit Alpha Channel. Basicly giving the functionality of the 444-4 format with 50% compression.
Both FS2000 and CFS2 support a 32 bit 888-8 format also. This has 24 bit RGB with an 8 bit Alpha channel
FS2002 continues the use of DXT started by CFS2. The DXT3 format is used in the default Aircraft to add Reflective values to a texture using the Alpha channel. This feature relies on the internal coding of the MDL so Aircraft created with FSDS will see the DXT3 Alpha channel as a normal Transparency channel while FS2002 Default Aircraft (and possibly new Aircraft created with the GMax design program) will see the Alpha channel as a "Reflection map".
CFS3 took a new direction and wen over almost exclusively to DDS format for textures. It also extended the use of DXT by adding DXT5.
