************************************************** ********************** *
* BLP FILE SPEC *
* by BlacKDlcK *
************************************************** ********************** *

The *.blp files are 2D picture files used on Blizzard Entertainment Games.
I guess 'blp' stands for "Blizzard Picture". Their main usage is TEXTUREs.
They suport different mip-maps (up to 16).

Those are used on the following Blizzard games:
1) "Warcraft III Reign of Chaos BETA"
2) "Warcraft III Reign of Chaos" (the retail and the demo version)
3) "Frozen Throne BETA"

Some important things:
a) "Warcraft III Reign of Chaos BETA" uses the first version of blp files, also
known as "BLP0".
b) All other games (for now) are using the "BLP1" version.
c) On "Warcraft III Reign of Chaos", they use both JPG-BLPs and Palleted-BLPs.
The JPG-BLPs DO NOT get goo compression on Blizzard archive format, "MPQs" since JPEGs are already "huffman compressed".
d) On "Frozen Throne BETA" they are only using Palleted-BLPs, since those get better compression on the "MPQs". They´re also using TGA´s (dunno why).

************************************************** ********************** *
* BLPHEADER *
************************************************** ********************** *
Signature As String * 4 'BLP0 or BLP1
ImageType As Long '0 for JPGblp, 1 for Paletted
hasAlpha As Long '0x8 = has alpha, 0x0 = no alpha
Width As Long 'Image Width
Height As Long 'Image Height
hasTeamColor As Long 'Got values of 3,4,5 here. If use >=5 on 'unit' textures, it won't show the team color.
isValid As Long 'Always =>0x1, if 0x0 the model that uses this texture will be messy.

************************************************** ********************** *
* MIPMAPTABLE (Only present if the file is a BLP1 *
************************************************** ********************** *
MipmapOffset(15) As Long
MipMapSize(15) As Long

************************************************** ********************** *
* GENERAL DATA (shared by all mip-maps) *
************************************************** ********************** *
If it is a JPEG-Blp we get:
JPEGHeaderSize as Long 'The lenght of the JPEGHeaderData.
JPEGHeaderData() as Byte 'The JPEGHeaderData.

If it is a Paletted-Blp, we get:
Palette(255) as RGBA 'RGBA is 4 bytes

************************************************** ********************** *
* MIP-MAP DATA *
************************************************** ********************** *
If this is a BLP0 file, then we must open a separate mipmap file (*.bxx), where 'xx'
is the mip-map level data. The lenght of the mip-map data is the len of the mip-map
file. For an example, to use a "Level 1" mipmap, the file name would be:
'name of blp file without .blp' + '.b01'

If this is a BLP1 file, then we can grab each mip-map data checking the table above.
Go to the MipMapOffset and read MipMapSize bytes.

Small tip:
Dont ask me why, but on BLP1 files Blizzard added some extra padding bytes between
the JPEGHeader and the first Mip-Map data. Those bytes can be safelly
erased if you fix each MipMappoffset entry on MipMapTable (subtract the ammount of
erased bytes).

************************************************** ********************** *
* Reading the mip-map data *
************************************************** ********************** *
If it is a JPEG-blp, we need to decompress the mipmap to get a RGBA picture.
Get the JPEGHeaderData + MipMapData and you'll have a JPEG-JFIF file.

If it is a Palleted-blp, we will have 2 bytes for each pixel of the picture:
ImageIndex as byte
AlphaIndex as byte

The ImageIndex reffer to the pallete.
The AlphaIndex reffer to a standard grayscale pallete.

************************************************** ********************** *
* blp1 minimap *
************************************************** ********************** *

The BLP file contain the JPEG header and the JPEG raw data separated.
BLP stands for "Blip" file which I guess is a "BLIzzard Picture".

Header:
char[4]: file ID ("BLP1")
int: 0 for JPGblp, 1 for Paletted
int: 0x00000008 = has alpha, 0x00000000 = no alpha
int: image width
int: image height
int: flag for team colors (usually 3, 4 or 5). If >=5 on 'unit' textures, it won't show the team color.
int: always 0x00000001, if 0x00000000 the model that uses this texture will be messy.
int: mipmap offset (offset from the begining of the file)
int[15]: unknown
int: mipmap size (header size) "h" (usually 0x00000270)
byte[h]: header
followed by 0 bytes until the begining of the jpeg data.
address=mipmap offset: raw jpeg data till the end of the file