Rtm Binarised File Format

UnBinarised Format

Binarised rtm was introduced for the Arma2 engine. For unbinarised see Rtm (Animation) File Format

Structure

RTMB
{
  RTMBHeader       Header;
  byte             Always1;              // ??
  XYZTriplet       Displacement;
  ulong            nFrames;              // 55 eg
  ulong            Generally0;           // ??
  ulong            nBones;               // same value as NoOfBones
  ulong            NoOfBones;            // 128 eg
  Asciiz           BoneNames[NoOfBones]; // "weapon\0\rightarm\leftarm\etc..."
  CompressedFloats FrameTimes;
  CompressedFrames Frames[nFrames];
}

BoneNames are the traditional Bis catenated strings. One after the other separated by '\0'. Unlike most others encountered in Bis file architecture, there is no final terminating double null because the count is already known.

RTMBHeader

RTMBHeader
{
 char[4]       Type;          //"BMTR" 
 ulong         Version;       // =3
}

CompressedFloats

CompressedFloats
{
 ulong nFrameTimes;          // should always be same as nFrames
 float Array[nFrameTimes];
}

This is the traditional Bis potentially compressed structure, where, if, the total bytes stored >=1024, the array is compressed (in lzo format)

CompressedFrames

CompressedFrames
{
 ulong   ThisFrameNoOfBones;               // Should always be same as nBones
 short   Transforms[ThisFrameNoOfBones][7];
}

The short values are compressed floats (7 in total) for each 'frame'

conversion to float is

float ShortToFloat(short value) {return ((float)1.0 / (65534)) * (value + 32767);}

this is suspiciously similar to ofp compressed floats

float = short * 0.045

4 floats probably are used to describe a quaternion that describes the rotation. the other 3 floats are then for the translation