dark-hammer / 3rdparty / assimp / src / assbin_chunks.h

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@page assfile .ASS File formats

@section over Overview
Assimp provides its own interchange format, which is intended to applications which need
to serialize 3D-models and to reload them quickly. Assimp's file formats are designed to
be read by Assimp itself. They encode additional information needed by Assimp to optimize
its postprocessing pipeline. If you once apply specific steps to a scene, then save it
and reread it from an ASS format using the same post processing settings, they won't
be executed again.

The format comes in two flavours: XML and binary - both of them hold a complete dump of
the 'aiScene' data structure returned by the APIs. The focus for the binary format
(<tt>.assbin</tt>) is fast loading. Optional deflate compression helps reduce file size. The XML
flavour, <tt>.assxml</tt> or simply .xml, is just a plain-to-xml conversion of aiScene.

ASSBIN is Assimp's binary interchange format. assimp_cmd (<tt>&lt;root&gt;/tools/assimp_cmd</tt>) is able to 
write it and the core library provides a loader for it.

@section assxml XML File format

The format is pretty much self-explanatory due to its similarity to the in-memory aiScene structure.
With few exceptions, C structures are wrapped in XML elements.

The DTD for ASSXML can be found in <tt>&lt;root&gt;/doc/AssXML_Scheme.xml</tt>. Or have   look
at the output files generated by assimp_cmd.

@section assbin Binary file format

The ASSBIN file format is composed of chunks to represent the hierarchical aiScene data structure.
This makes the format extensible and allows backward-compatibility with future data structure
versions. The <tt>&lt;root&gt;/code/assbin_chunks.h</tt> header contains some magic constants
for use by stand-alone ASSBIN loaders. Also, Assimp's own file writer can be found
in <tt>&lt;root&gt;/tools/assimp_cmd/WriteDumb.cpp</tt> (yes, the 'b' is no typo ...).


1. File structure:

| Header (500 bytes) |
| Variable chunks    |

2. Definitions:

integer	is four bytes wide, stored in little-endian byte order.
short	is two bytes wide, stored in little-endian byte order.
byte	is a single byte.
string  is an integer n followed by n UTF-8 characters, not terminated by zero
float	is an IEEE 754 single-precision floating-point value 
double	is an IEEE 754 double-precision floating-point value 
t[n]    is an array of n elements of type t

2. Header:

byte[44]	Magic identification string for ASSBIN files.

integer		Major version of the Assimp library which wrote the file
integer		Minor version of the Assimp library which wrote the file
                match these against ASSBIN_VERSION_MAJOR and ASSBIN_VERSION_MINOR

integer		SVN revision of the Assimp library (intended for our internal
            debugging - if you write Ass files from your own APPs, set this value to 0.
integer		Assimp compile flags

short		0 for normal files, 1 for shortened dumps for regression tests 
                these should have the file extension assbin.regress

short       1 if the data after the header is compressed with the DEFLATE algorithm,
            0 for uncompressed files.
                   For compressed files, the first integer after the header is
                   always the uncompressed data size
byte[256]	Zero-terminated source file name, UTF-8
byte[128]	Zero-terminated command line parameters passed to assimp_cmd, UTF-8 

byte[64]	Reserved for future use
---> Total length: 512 bytes

3. Chunks:

integer		Magic chunk ID (ASSBIN_CHUNK_XXX)
integer		Chunk data length, in bytes 
                (unknown chunks are possible, a good reader skips over them)

byte[n]		length-of-chunk bytes of data, depending on the chunk type

Chunks can contain nested chunks. Nested chunks are ALWAYS at the end of the chunk,
their size is included in length-of-chunk.

The chunk layout for all ASSIMP data structures is derived from their C declarations.
The general 'rule' to get from Assimp headers to the serialized layout is:

   1. POD members (i.e. aiMesh::mPrimitiveTypes, aiMesh::mNumVertices), 
        in order of declaration.

   2. Array-members (aiMesh::mFaces, aiMesh::mVertices, aiBone::mWeights), 
        in order of declaration.

   2. Object array members (i.e aiMesh::mBones, aiScene::mMeshes) are stored in 
      subchunks directly following the data written in 1.) and 2.)

	Of course, there are some exceptions to this general order:


   - The root node holding the scene structure is naturally stored in
     a ASSBIN_CHUNK_AINODE subchunk following 1.) and 2.) (which is 
	 empty for aiScene).


   - mTextureCoords and mNumUVComponents are serialized as follows:

   [number of used uv channels times]
       integer mNumUVComponents[n]
       float mTextureCoords[n][mNumUVComponents[n]]

       -> more than AI_MAX_TEXCOORD_CHANNELS can be stored. This allows Assimp 
	   builds with different settings for AI_MAX_TEXCOORD_CHANNELS to exchange
	   data. Unlike the in-memory format, only the used components of the 
	   UV coordinates are written to disk. If mNumUVComponents[0] is 1, the
	   corresponding mTextureCoords array consists of mNumTextureCoords*1 
	   single floats.

   - The array member block of aiMesh is prefixed with an integer that specifies 
     the kinds of vertex components actually present in the mesh. This is a 
	 bitwise combination of the ASSBIN_MESH_HAS_xxx constants.


   - mNumIndices is stored as short
   - mIndices are written as short, if aiMesh::mNumVertices<65536


   - mParent is omitted


   - mAttenuationXXX not written if aiLight::mType == aiLightSource_DIRECTIONAL
   - mAngleXXX not written if aiLight::mType != aiLightSource_SPOT


   - mNumAllocated is omitted, for obvious reasons :-)



// these are the magic chunk identifiers for the binary ASS file format
#define ASSBIN_CHUNK_AICAMERA					0x1234
#define ASSBIN_CHUNK_AILIGHT					0x1235
#define ASSBIN_CHUNK_AITEXTURE					0x1236
#define ASSBIN_CHUNK_AIMESH						0x1237
#define ASSBIN_CHUNK_AINODEANIM					0x1238
#define ASSBIN_CHUNK_AISCENE					0x1239
#define ASSBIN_CHUNK_AIBONE						0x123a
#define ASSBIN_CHUNK_AINODE						0x123c
#define ASSBIN_CHUNK_AIMATERIAL					0x123d

#define ASSBIN_MESH_HAS_NORMALS						0x2
#define ASSBIN_MESH_HAS_COLOR_BASE					0x10000


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