Breakable (RW Section)

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RW Stream Section
Breakable
0x0253F2FD

Breakable, formerly Breakable Model, is one of Rockstar's custom sections used in GTA San Andreas. It contains information on how to split breakable objects when they are hit. An object including this section has to be defined in object.dat.

The typical location in a SA dff section hierarchy is Clump > Geometry List > Geometry > Extension > Breakable.

Magic number

The initial 4 bytes sequence signals the usage of the extension:

UINT32  magicNumber

If zero, the section ends here. A non-zero value has no particular meaning and can be any (see Meaningless values).

Header

There is a 52 byte header which holds information about the amount of data arrays that follow:

UINT32  posnRule (0 = OBJECT_ORIGIN, 1 = COLLISION_ORIGIN)
// Vertex data
UINT16  numVertices
UINT16  
UINT32  (assumed offset to verts, unused)
UINT32  (assumed offset to texCoords, unused)
UINT32  (assumed offset to preLitLum, unused)
// Triangle data
UINT16  numTriangles
UINT16  
UINT32  (assumed offset to vertIndices, unused)
UINT32  (assumed offset to matIndices, unused)
// Material data
UINT16  numMaterials
UINT16  
UINT32  (assumed offset to textures, unused)
UINT32  (assumed offset to textureNames, unused)
UINT32  (assumed offset to textureMasks, unused)
UINT32  (assumed offset to ambientColors, unused)

The position rule imposes whether to calculate the position relatively to the collision model or to the clump/atomic RwFrame. See Meaningless values for clarifications about the unused fields.

Vertex data

FLOAT[3]    verts[numVertices]
FLOAT[2]    texCoords[numVertices]
BYTE[4]     preLitLum[numVertices] (RGBA)

Triangle data

UINT16[3]   vertIndices[numTriangles]
UINT16      matIndices[numTriangles]

Material data

Each polygon group sharing the same material is treated as a separate fragment when the object is split up:

CHAR[32]    textureNames[numMaterials]
CHAR[32]    textureMasks[numMaterials]
FLOAT[3]    ambientColors[numMaterials] (RGB normalized in range [0,1])

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