Halo 2

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Map File Format (Iron_Forge whitepaper)

Retrieved from old.halomods.com.

Halo 2 .map file format whitepaper originally by Iron_Forge.

Filename: H2WhitePaper.doc

Created: 11/21/2004, 12:13:00, Iron_Forge.

Revision: 0.9b

1 - General Information

1.1 - Introduction

Greetings. My name is Iron_Forge, and I have been working on and off with Halo map files of one type or another for a little over a year now. I have remained active in all areas of map formatting of Halo 1 for the xbox as well as the pc. Odds are if you have used an application for Halo 1, I have had a hand in it, or the information that led to its conception.

I have been working on the Halo 2 map format since its release, and this document serves as a collection of the information I have compiled with the help of good friends MonoxideC and ViperNeo. Applying my experience from Halo 1 and other projects, I am one of a handful of people who could be considered experts on the map file formats. Using this document, I hope to pass this on to you.

Many things are not contained within this document, for the simple reason of I did not figure out how they work (the BSP is a good example.) That’s not to say these things are still unknown. ViperNeo had the BSP information completed the same time we were working on models together, due to the strong similarity between them.

1.2 - Glossary

  • dword – 4 bytes of data (double word)
  • word – 2 bytes of data
  • primary magic – A value used to increase offsets, allowing large areas of data to be moved without modifying the offsets contained within it.
  • secondary magic – A value used to increase offsets, allowing large areas of data to be moved without modifying the offsets contained within it, primarily used for meta.
  • pure offset – A value which represents an offset in the file that has not been modified in any way
  • raw offset – A pure offset whose 2 most significant bits represent the file the offset references
  • primary magic offset – A pure offset whose value has been increased by the primary magic value
  • secondary magic offset – A pure offset whose value has been increased by the secondary magic value

2 - Map Information

2.1 - Map Layout

The Halo 2 map files can be broken up into the following sections:

  • header
  • sound raw data
  • model raw data
  • bsp model raw data
  • model animation raw data
  • bsp structure
  • script references
  • file names
  • unicode strings raw data
  • other
  • texture raw data
  • object index
  • index padding
  • object meta information
  • the cache (where applicable)

2.2 - Processing

When Halo 2 is loaded, it will create cache files (copying the original files to the hard drive of the xbox). The shared and single player shared map files are exceptions to this rule, most likely to lower the load times of the game starting, and each map being processed. If your installation has valid bink video files, these will be played during load times, otherwise a progress text will appear on the screen showing the percentage copied.

All loaded files are signed (see section on encryptomatic signature), and should a loading map fail, the engine will retry the copy twice more before giving a “dirty disk” error, or a “map failed to load” error, depending on the map.

Upon loading a map, only the required resources are placed in memory. As objects appear on screen, the data for them is streamed from the shared files, replacing the very low copy kept in memory with a much richer and more detailed counterparts. This process allows even multiplayer maps to have access to several hundred megabytes of information, while remaining within the limitations of the xbox hardware.

2.3 - Map Header

The map header1 is 2048 bytes just as previous versions of Halo. The version tag is now 8. The index offset is a pure offset pointing to the index header, followed by the meta start, which when added to the index offset will point to the beginning of the meta area. Map origin will define the path (and file) the cache was created from, and as such is only defined in the cache files.

2.3.1 - File Table

The file table contains full paths for each object in relative order (first filename is for the first object.) The strings are standard ASCII, with a null termination and no padding is used regardless of where the string terminates.

The file table index contains unsigned integers defining the offset which each string begins, also relative. This allows the file table to be read as a single block of characters, and each object to be issued a pointer to the beginning of its string.

2.3.2 - Encryptomatic Signature

The encryptomatic signature is created by xoring every dword after the header together. It is my belief that this value has the single purpose of validating maps copied correctly, and was not used to “thwart” would be modders.

2.3.3 - Script References

Script references link some object to a specific event. The string table defining these references is in the same format as the file table, including an index. They can often be found following dependencies such as effect dependencies. This would link that effect to be triggered by a given event, such as a button being pressed, or an item being picked up. The reference themselves consist of a pair of words, the first being the index to the string in the table, the second being the length of the script reference string.

2.4 - Index Header

The first value in the index header remains the constant used to calculate magic. The object index offset here is a primary magic offset, and points to the object index.

2.4.1 - Tag List

Directly following the index header is the tag list. This list contains all used tags in the map file, and defines their object hierarchy. This allows the engine to know for example, that all vehicles are a sub class of the unit class, which is a sub class of the object class. I believe the wildcard tags are used as a way of using the primary tag without its parents, though this is just speculation.

2.4.2 - Object Index

The object index is a recursively-constructed collection defining all objects in the map. The objects identifier is defined here, which is used to reference the object from all other areas of the map file. The identifier is composed of two short values, each are incremented equally throughout the index. The meta offset is a secondary magic offset which points to the beginning of the objects meta.

2.4.3 - Primary and Secondary Magic

The magic values are used to allow moving large blocks of data without having to modify the data itself. Using a magic value applied to all offsets, after moving the data x bytes, the magic only needs to be increased or decreased 8 to correct all offsets, rather than each offset needing re-calculation. Primary magic is still calculated by magic constant - (index header offset) + sizeof(index header)). Secondary magic, which is now used instead of primary magic for meta related offsets, is primary magic + sizeof(BSP). Since we cannot obtain the size of the BSP object without using secondary magic (it is located in the scenery tag), we use the known offset of the meta start and the secondary magic offset of the first object to calculate this value.

3 - Objects

3.1 - Raw Offsets

Raw offsets in Halo 2 have no magic applied to them. However, they can reference the current map file, or the three shared files. To do this, it reserves the two most significant (highest) bits to define the referencing file. These are defined as: 002 being local file, 012 being mainmenu.map, 102 being shared.map, and 112 being single_player_shared.map.

When referencing a raw offset, one should first determine the file being referenced, remove those two bits from the offset value (and with 0x3FFFFFFF), and then seek to that offset in the correct file to find the referenced data. Given the size of the shared files, it is possible that the third most significant bit is also reserved for sharing new downloadable content in the future, but this would just be speculation.

3.2 - Unicode Strings

Unicode strings are built to allow for up to nine languages. The globals object defines where each language block is located, and its related information (size, string count, etc.) as needed. Each unicode string object then contains two shorts per language, the first defining the offset (as a string count) in the language block that the unicode object begins, and the second defining how many strings are in the object.

This method allows the multiplayer maps to be identical for every version and region of Halo 2. The engine can simply detect you xbox language settings, and supply the correct string(s) form the language block.

3.3 - Bitmaps & Textures

Bitmap objects are collections of the textures in Halo 2, and their layout is rather straightforward. Each texture is allowed up to six levels of detail. Each level of detail is identical to its predecessors first mipmap. So if the first quality level were 256x256, the following would be 128x128. Each level of detail however still contains its own entire set of mipmaps. I suspect this goes further towards Halo 2’s efficient use of memory management.

Each bitmap object may also contain several images, usually used where options between similar sets of images are needed (such as multiple level images in the main menu.) These will be represented by the bitm struct reflexive. Each bitmap may be extracted as if it were its own object.

Referencing the source to HME/HMT, we can find the different image formats for the different image objects. In addition to these types, 0x11 and 0x12 are both single channel images (you may extract them as A8 if using the common DDS), and are used for bump maps, and light maps (respectively.)

Many images are still swizzled (a technique for faster memory copies), and this information may also be referenced from the HME/HMT sources.

3.4 - Sounds

Sounds were probably the most enjoyable piece of Halo 2 to work on. They entwine with an “ugh!” object named “I’ve got a lovely bunch of coconuts”, a song done by the amazing comedic group Monty Python. I cannot help but believe this system was done as an easter egg designed just for me as “the curious modder”. To Bungie, I thank you (unless of course this was designed to keep us from removing sounds, in which case I sincerely apologize.)

In each sound meta, there is an index and chunk count that references a block in the fifth reflexive in the coconuts object. This block has another index and chunk count, referencing the sixth reflexive in the coconuts object. These chunks reference “option” sounds, such as several different sound choices for entering a vehicle.

Each item in the sixth block contains another index and chunk count, this time referencing the ninth reflexive in the coconuts object. The ninth reflexive contains the size and raw offset for each piece of the sound.

Sounds in Halo 2 are xbox adpcm or WMA, depending on the type byte. The WMA sounds can be assembled completely from the raw data pieces. The xbox adpcm pieces require the header be written.

If the type byte is 1, then the sound is an adpcm, mono, and 22050kbps sound file. Type 2 is also adpcm, stereo, and 44100kbps sound file. Type 3 is a WMA sound file. There is more to the sound formatting than this, however this was mare than enough for me to extract all the sounds.

3.5 - Models

Models in Halo 2 use a compressed format based on a bounding box. This bounding box can be found in the first reflexive of the model meta. Using its constraints for each value relevant to the models, the uncompressed value can be found using the formula (((shortValue + 32768) / 65535) * (maxValue – minValue)) + minValue.

The model raw data block now contains a header, footer, and several resource chunks. The header contains information regarding how many chunks are in each resource block, allowing you to determine which block contains the information needed (for example, if a given block has 0 chunks, then it will not have a corresponding resource block). The important resource blocks are the mesh information block (containing mesh information), the indices block (containing the indices for the triangle strip), the vertices block (containing at minimum 3 shorts defining the x, y, and z of the vertices), the UV map (containing the compressed UV points.), and the bone map.

The third dword (as an unsigned integer) in each mesh information block defines how many indices are in that mesh. The indices are placed in order, so each meshes indices can be found after its predecessor in the indices resource block.

The vertices are stored with several sized blocks within their resource block, however the x, y, and z points are still represented by the first 3 shorts respectively. The size of each vertex block can be determined by the type bytes in the model meta. Each short must then be decompressed using the above-mentioned formula and their own constraint value, min x and max x for x, and so on.

If the given vertex type has more than 6 bytes, it is followed by the bone references and weights of this vertex. Both are one byte in length, and the bone references are sorted. Therefore if a bone with a value of 0 is read in any position other than the first, this bone reference should be discarded, as should all that follow. Following the bone references are their weights, which are also one byte in length, and can be considered compressed. The weights are a value between 0 an 1 once uncompressed, thus a byte with a weight of 128 will have a weight of 0.5 (or 50% deformation based on this bone.) The exception to this is the 8 byte vertices, where the two bytes following are both bones. If both are set, they each have a weight of 0.5, and if only one is set it is given full weight.

The UV’s are slightly more complicated. They are compressed in the same fashion as the vertices. However, while UV’s must always remain between 0 and 1, their constraints are not governed by the same limits. The resulting uncompressed values can be fixed through “looping” them. If the value is 1.3, the resulting value would be 0.3, and given the value -0.3, the resulting value would be 0.7. The easiest way to accomplish this is to mod the resulting value by 1, and then if the value is negative, subtract it from 1.

Since the bones have to act over several different pieces, each raw model block has a bone map, relating the bone byte to the correct bone id. This is a byte array, so if a vertex references bone 0, then boneMap[0] will provide the correct bone id.

Back to the meta, the sixth reflexive in the model meta defines the bone hierarchy of the model. When parent, child, or sibling is none, the value will be set to 0xFFFF. These chunks are the bones which are mapped to from the raw data. The name is a script reference, and defines what the bone is called.

The second reflexive defines all the level of details (LOD) for the model pieces. The name is again a script reference defining what this particular LOD is called. This is followed by a reflexive. This reflexive is for all the different options for the particular LOD (for example: base, default, damaged, etc.) Each of these reflexives consist of another script reference name, defining what this option is referred to as, followed by a series of 5 shorts. These shorts refer to the piece of the model which makes up one of the 5 LODs for this option. The last short (following the 5 LODs), defines the piece of the model which has the highest LOD (this should be equal to the 5th LOD value.) If a model only has 3 LODs, the first three LOD values will be the same, defining one piece to be used for all three levels.

The seventh reflexive in the model meta defines a series of locations defining everything from where lights and other effects are located on a model, to where the characters place their hands while using the model. These are set by a script reference to link the point to, and the points location data.

3.6 - Other Tags

For the most part, objects are quite similar to their Halo 1 counterparts. Usually there has been some general compacting of the data (the tags have been cleaned up, unused values removed), or a reflexive added here and there. Notable exceptions that I haven’t written about here (as lack of time and motivation kept me away) are the model animations, which now have large blocks of raw data.

4 - In Closing

4.1 - Conclusion

In closing, I would like to say that not all the information enclosed here is guaranteed to be accurate. It is composed of my findings, and how I interpreted them at the time. Much of the structs are incomplete, as I tend to not write down things I figure out while seeking other answers, and I tried to only include solid information, instead of all my random notes.

The information contained within these pages should be enough to get any one started, and take them to the point of being able to obtain any of the above items, and replace them with their own creations.

I would like to thank all of you who read this far (and bothered reading this), and to you all, happy modding.

4.2 - Acknowledgements

I would also once again like to thank MonoxideC and ViperNeo for their help in this. While they may remain modest, both were invaluable in explaining things I didn’t fully understand, bouncing ideas off, and just helping out anyway they could. The community is better for having them, and I better for knowing them.

5 - Appendix I - Structures

struct mapHeader {
  char[4] head;
  int version;
  int filesize;
  int zero;
  int indexOffset;
  int metaStart;
  dword[2] unknown;
  char[32] mapOrigin;
  char[32] build;
  byte[20] unknown;
  int unknown;
  int offsetToStrangeFileStrings;
  int unknown;
  int offsetToSomething;
  int scriptReferenceCount;
  int sizeOfScriptReference;
  int offsetToScriptReferenceIndex;
  int offsetToScriptReferenceStrings;
  byte[36] unknown;
  char[32] mapName;
  int zero;
  char[32] scenarioPath;
  byte[224] zero;
  int unknown;
  int fileCount;
  int fileTableOffset;
  int fileTableSize;
  int filesIndex;
  int signature;
  byte[1320] zero;
  char[4] foot;

struct indexHeader {
  int primaryMagicConstantMagic;
  int tagListCount;
  int objectIndexOffset;
  int scenarioID;
  int tagIDStart;
  int unknown;
  int objectCount;
  char[4] tags;

struct tagListEntry {
  char[4] objectClass;
  char[4] parentClass;
  char[4] grandparentClass;
struct objectEntry {
  char[4] tag;
  int ID;
  int offset;
  int metaSize;

struct unicMeta {
  uint[4] zero;
  short lang1Offset;
  short lang1Count;
  short lang2Offset;
  short lang2Count;
  short lang3Offset;
  short lang3Count;
  short lang4Offset;
  short lang4Count;
  short lang5Offset;
  short lang5Count;
  short lang6Offset;
  short lang6Count;
  short lang7Offset;
  short lang7Count;
  short lang8Offset;
  short lang8Count;
  short lang9Offset;
  short lang9Count;

struct bitmMeta {
  byte[68] data;
  struct image {
    char[4] bitm;
    ushort width;
    ushort height;
    ushort depth;
    ushort type;
    ushort format;
    ushort flags;
    ushort regPointX;
    ushort regPointY;
    ushort mipMapCount;
    ushort pixelOffset;
    uint zero;
    uint[6] offset;
    uint[6] size;
    uint identifier;
    byte[36] unknown;

struct sndMeta {
  dword unknown;
  byte format;
  byte[3] unknown;
  short index;
  byte chunkCount;
  byte unknown;
  dword[2] unknown;

struct ughMeta {
  struct {}
  struct {}
  struct {
    scriptRef sound;
  struct {}
  struct soundOptions {
    dword[2] unknown;
    short index;
    short chunkCount;
  struct soundPieces {
    dword[3] unknown;
    short index;
    short chunkCount;
  struct {}
  struct {}
  struct rawSound {
    uint rawOffset;
    uint size;
    uint eff;
  struct {}
  struct {}

struct modeMeta {
  scriptRef modelName;
  dword val2;
  dword val3;
  dword zero;
  dword zero;
  struct boundingBox
    float minX;
    float maxX;
    float minY;
    float maxY;
    float minZ;
    float maxZ;
    float minU;
    float maxU;
    float minV;
    float maxV;
    dword:4 zero;
  struct LODs
    scriptRef modelPiece;
    word sval1; // FFFF
    word sval2; // 0000
    struct ref2.1
      scriptRef modelType;
      word LODPiece1;
      word LODPiece2;
      word LODPiece3;
      word LODPiece4;
      word LODPiece5;
      word LODPieceHigh;
  struct pieces
    dword unknown;
    ushort vertCount;
    ushort unknown;
    byte[12] val1;
    ushort type;
    ushort unkown;
    dword val;
    dword[2] zero;
    dword[3] val;
    dword[2] zero;
    uint rawOffset;
    uint size;
    uint headerSize;
    dword val4;
    struct rsrc
      word val;
      word val;
      word val;
      word val;
      uint size;
      uint offset;
    dword identifier;
    dword val5;
    dword eff;
  struct ref4
    dword zero;
  struct ref5
    dword val1;
    dword:2 zero;
  dword[3] zero;
  struct bones
    scriptRef boneName
    ushort parent;
    ushort firstChild;
    ushort nextSibling;
    word val1;
    float distanceFromParent;
  dword[2] zero;
  struct points
    scriptRef pointName;
    struct points
      short; // 0xFFFF
      float[7] val;
      dword zero;
  struct shaders
    dependancy shad;
    dependancy shad;
    dword:4 zero;
  dword[7] zero;

struct modelHeader {
  char[4] blkh;
  uint size;
  uint informationChunks;
  uint zero;
  uint unkChunks;
  uint zero;
  uint unk2Chunks;
  uint[3] zero;
  uint indicesChunks;
  uint[5] zero;
  uint unk3Chunks;
  uint[10] zero;
  uint boneChunks;
  uint[2] zero;