BLP |
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Contents |
BLP Files
BLP files store textures with precalculated mipmaps. Most of the textures are compressed with DXTC, except for a few palettized detail textures.
Header
| Offset | Type | Description |
|---|---|---|
| 0x00 | char[4] | always 'BLP2' |
| 0x04 | uint32 | Version, always 1 |
| 0x08 | uint8 | Compression: 1 for uncompressed, 2 for DXTC |
| 0x09 | uint8 | Alpha channel bit depth: 0, 1 or 8 |
| 0x0A | uint8 | Something about alpha? (compressed, alpha:0 or 1): 0, (compressed, alpha:8): 1, uncompressed: 2,4 or 8 (mostly 8) |
| 0x0B | uint8 | when 0 there is only 1 mipmaplevel. compressed: 0, 1 or 2, uncompressed: 1 or 2 (mostly 1) |
| 0x0C | uint32 | X resolution (power of 2) |
| 0x10 | uint32 | Y resolution (power of 2) |
| 0x14 | uint32[16] | offsets for every mipmap level (or 0 when there is no more mipmap level) |
| 0x54 | uint32[16] | sizes for every mipmap level (or 0 when there is no more mipmap level) |
Compressed textures
For compressed textures, DXT1 or DXT3 (possibly DXT5 depending on the header values) data follows, for every mipmap level. Unused mipmap levels have an offset and size of 0.
Detailed description of the DXTC formats can be found on MSDN
Uncompressed textures
After the header, 256 32-bit BGRA values make up the palette. The image data (for each mipmap level) consists of 8-bit indices into this palette.
If there is an alpha channel, then transparency data follows the image data in each mipmap level. If the Alpha bit depth is 0, there is no alpha channel. If the Alpha bit depth is 1, the alpha data is 8 alpha bits backed into each byte. If the Alpha big depth is 8, there is one byte per alpha value.
