MagicaVoxel-file-format-vox-extension.txt

* there can be multiple SIZE and XYZI chunks for multiple models; model id is their index in the stored order
* the palette chunk is always stored into the file, so default palette is not needed any more
* the MATT chunk is deprecated, replaced by the MATL chunk, see (4)
* (a), (b), (c) are special data types; (d) is the scene graph in the world editor

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(a) STRING type

int32   : buffer size (in bytes)
int8xN	: buffer (without the ending "\0")

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(b) DICT type

int32	: num of key-value pairs

// for each key-value pair
{
STRING	: key
STRING	: value
}xN

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(c) ROTATION type

store a row-major rotation in the bits of a byte

for example :
R =
 0  1  0
 0  0 -1
-1  0  0 
==>
unsigned char _r = (1 << 0) | (2 << 2) | (0 << 4) | (1 << 5) | (1 << 6)

bit | value
0-1 : 1 : index of the non-zero entry in the first row
2-3 : 2 : index of the non-zero entry in the second row
4   : 0 : the sign in the first row (0 : positive; 1 : negative)
5   : 1 : the sign in the second row (0 : positive; 1 : negative)
6   : 1 : the sign in the third row (0 : positive; 1 : negative)

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(d) Scene Graph

T : Transform Node
G : Group Node
S : Shape Node

     T
     |
     G
    / \
   T   T
   |   |
   G   S
  / \
 T   T
 |   |
 S   S

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(1) Transform Node Chunk : "nTRN"

int32	: node id
DICT	: node attributes
	  (_name : string)
	  (_hidden : 0/1)
int32 	: child node id
int32 	: reserved id (must be -1)
int32	: layer id
int32	: num of frames (must be 1)

// for each frame
{
DICT	: frame attributes
	  (_r : int8) ROTATION, see (c)
	  (_t : int32x3) translation
}xN

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(2) Group Node Chunk : "nGRP" 

int32	: node id
DICT	: node attributes
int32 	: num of children nodes

// for each child
{
int32	: child node id
}xN

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(3) Shape Node Chunk : "nSHP" 

int32	: node id
DICT	: node attributes
int32 	: num of models (must be 1)

// for each model
{
int32	: model id
DICT	: model attributes : reserved
}xN

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(4) Material Chunk : "MATL"

int32	: material id
DICT	: material properties
	  (_type : str) _diffuse, _metal, _glass, _emit
	  (_weight : float) range 0 ~ 1
	  (_rough : float)
	  (_spec : float)
	  (_ior : float)
	  (_att : float)
	  (_flux : float)
	  (_plastic)
	  
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(5) Layer Chunk : "LAYR"
int32	: layer id
DICT	: layer atrribute
	  (_name : string)
	  (_hidden : 0/1)
int32	: reserved id, must be -1