Editing WoW:BLP file (section)

=== BLP version 2 header ===
 struct blp2header {
   uint8_t    ident[4];           // "BLP2" magic number
   uint32_t   type;               // 0 = JPG, 1 = BLP / DXTC / Uncompressed
   uint8_t    compression;        // 1 = BLP, 2 = DXTC, 3 = Uncompressed
   uint8_t    alpha_depth;        // 0, 1, 4, or 8
   uint8_t    alpha_type;         // 0, 1, 7, or 8
   uint8_t    has_mips;           // 0 = no mips, 1 = has mips
   uint32_t   width;              // Image width in pixels, usually a power of 2
   uint32_t   height;             // Image height in pixels, usually a power of 2
   uint32_t   mipmap_offsets[16]; // The file offsets of each mipmap, 0 for unused
   uint32_t   mipmap_lengths[16]; // The length of each mipmap data block
   uint32_t   palette[265];       // A set of 256 ARGB values used as a color palette
 } blp2header;

==== Notes ====
* The actual number of 'mip' levels determined by image size
* For '''WoW''' 'type' should always be 1. '''WoW''' does not currently use JPG format. BLP files using JPG compression is beyond the scope of this article.
* '''WoW''' has shipped with a small number of BLPs with dimensions that are not powers of two; 768x128 is used for many cube map textures, for example. In this case, the final stored mipmap may not be 1x1. (this last part may not be accurate)
* Compression type 3 'Uncompressed' appeared in Cataclysm, and data layout is canonical A8R8G8B8, which is essentially uncompressed 24-bit color with 8-bit alpha.
* The header always includes a 256-entry color table. Each entry a 32-bit BGRA 8888 value. This table is only used for BLP format image data, but is present in all BLPs regardless.