lowmiptextures - themeldingwars/Documentation GitHub Wiki

lowmiptextures.pak lives in system/vt next to the virtual texture files. It is the low mip fallback pack: the smallest mip levels of every texture in the virtual texture, bundled into one archive so the renderer always has something to draw while the real tiles are still being streamed in. The client side of this is lowmiptexturecache.cpp, and fx.lowMipTextureThreshold is the cvar that decides when it gets used.

Unlike vtex it is a completely ordinary archive: an LZMA compressed index followed by one LZMA compressed block per texture. Everything needed to unpack it is in the file itself, no .vtex_idx involved.

010 Editor Templates

lowmiptextures.bt - the container
lowmiptextures.index.bt - run this on the decompressed index

Implementations

Forgery unpacks it, see the vtex test-mips command in forgery.js

Format

Little endian.

Container

Field	Type	Notes
`magic`	`char[4]`	`LMTD`
`indexOriginalSize`	`uint32`	Decompressed size of the index
`indexCompressedSize`	`uint32`	Compressed size of the index
`index`	`byte[indexCompressedSize]`	LZMA
`blocks`	`byte[]`	The texture data, to the end of the file

blocks starts at offset 12 + indexCompressedSize. Call that the base offset, every compressedOffset in the index is relative to it.

Index

Once decompressed:

Field	Type
`rowCount`	`uint32`
`rows`	`Row[rowCount]`

Row

Field	Type	Notes
`path`	`cstring`	Asset path of the texture
`unknown`	`uint32`
`width`	`uint32`
`height`	`uint32`
`unknown`	`uint32`
`pixelCount`	`uint32`
`unknown`	`uint32[3]`
`imageFormat`	`char[20]`	Null terminated and zero padded, e.g. a DXT format name
`unknown`	`uint32[6]`
`decompressedSize`	`uint32`	Size of this texture's data once decompressed
`compressedOffset`	`uint32`	Offset of the block, relative to the base offset
`compressedSize`	`uint32`	Size of the block

Rows are variable length because of the leading path string, so the index has to be walked from the start.

Blocks

Each block is a standalone LZMA stream: slice compressedSize bytes at baseOffset + compressedOffset and decompress to exactly decompressedSize bytes. The rows appear in offset order in practice, but nothing depends on that.

Open questions

Nine of the uint32 fields in a row are unnamed. width, height and pixelCount are confirmed by their values being consistent with each other, the rest are not. Comparing a row against the corresponding entry in vtex_idx for the same asset would probably identify several of them at once.
The exact width of the imageFormat field. It reads as a short null terminated string followed by padding that always sums to 20 bytes, but whether the client treats that as one fixed 20 byte field or as a string plus separate fields has not been checked.