.bti file format

http://www.amnoid.de/gc/

Version 1.02

NOTE: Some .bti files are Yaz0-compressed (if the first 4 bytes are 'Yaz0'),
if this is the case, you have to uncompress them. Check out yagcd or
www.amnoid.de/gc/ on how to do that.

A bti file stores a single image, but can store several mipmaps. The file
starts with a TextureHeader (which is used in the TEX1 section of
bmd/bdl and jpa files to store textures as well). It looks like this:

struct TextureHeader
{
  u8 format;  //data format - seems to match tpl's format (see yagcd)
  u8 unknown;
  u16 width;
  u16 height;

  /*
    from gx.h:
    0: clamp to edge
    1: repeat
    2: mirror
  */
  u8 wrapS;
  u8 wrapT;

  u8 unknown3;
  u8 paletteFormat; //palette format - matches tpl palette format (-> yagcd)
  u16 paletteNumEntries;
  u32 paletteOffset; //palette data


  u32 unknown5;
  u16 unknown6; //prolly two u8s, first is 5 or 1, second 1 most of the time
  u16 unknown7; //0 most of the time, sometimes 0x10, 0x18, 0x20, 0x28
  u8 mipmapCount;
  u8 unknown8;
  u16 unknown9;

  u32 dataOffset; //image data

  //some of the unknown data could be render state?
  //(lod bias, min/mag filter, ...)
};

Offsets are relative to TextureHeader (this is important in bmd/bdl files).
Check the accompanying source code for details.

Details on dxt3 compression can be found here:
http://www.hardwarecentral.com/hardwarecentral/reports/140/4

Let me know if you discover what the unknown fields mean:
http://www.emutalk.net/showthread.php?s=ec36fcfefebb44cd0dddfebf656db018&t26919
thakis

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