Left 4 Dead — XeNTaX Forum Knowledge

Extracted and organized from XeNTaX forum discussions (2008–2017). Covers Left 4 Dead PC (Source engine) and Xbox 360 (L4D360) formats.

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1. VPK Archives (PC — Source engine)

Topic 3219 (2008). With the L4D demo release, Valve shipped game files not in the standard .gcf format used by other Source games, but in a series of .vpk files. These VPKs differ from the earlier .vpk used in Vampire: The Masquerade — Bloodlines. (Mystfit, 2008-11-13)

Tools (Rick/Gibbed, 2008-11-14):

• Gibbed.Valve.ExtractPackage — VPK extraction tool by Rick.
• Requires .NET Framework 2.0; without it, throws System.IO.FileNotFoundException for System.Windows.Forms. (asmxtx, 2008-11-26; fix: nicoli_s)

Practical note: On XP, the tool fails silently unless the GUI .EXE is patched to console mode; missing .NET 2.0 is the usual cause.

2. Xbox 360: VTFX Textures

Topic 3257 (2008–2017). The Xbox 360 version of L4D uses a slightly modified version of Valve's VTF format, called VTFX. (TheGeneral, 2008-12-19)

VTFX File Header

TheGeneral's initial structure (files are big-endian — byte-swap before viewing):

struct VTFXFileHeader {
 int fileSignature; // 0x56544658 ("VTFX")
 int version1; // 0x00000360
 int version2; // 0x00000008
 int headerSize; // 0x00000044
 int unknown;
 short width;
 short height;
 short unknown; (x4)
 float reflectivityX;
 float reflectivityY;
 float reflectivityZ;
 float bumpMapScale;
 int imageFormat;
 int unknown; (x3)
 int headerSize2; // 0x00000044
};

Key header offsets (Acewell, 2017-12-01):

• 0x0C — LZMA_OFF (long, big-endian): offset where LZMA data begins
• 0x14 — width (2 bytes)
• 0x16 — height (2 bytes)

Structure of the embedded image

• The image data inside is LZMA-compressed (cfarl, 2017-11-20).
• The decompressed payload is a .textures file containing a DXT5 big-endian image (1024×512 example).
• Mipmap order is inverted: the smallest mip comes first, the largest (main) mip is last in the uncompressed data. (fatduck, 2009-02-04; Acewell, 2017-12-01)
• DXT5 data size = width × height. To extract the main mip, count back width × height bytes from the end of the decompressed file.

LZMA payload header (at LZMA_OFF, little-endian)

Offset	Type	Field
+0x00	dstring(4)	LZMA id
+0x04	long	SIZE (uncompressed size)
+0x08	long	ZSIZE (compressed size)
+0x0C	dstring(5)	LZMA_PROP (5-byte LZMA properties)

QuickBMS extraction script (cfarl, 2017-12-04)

# script for QuickBMS http://aluigi.altervista.org/quickbms.htm

endian big
idstring "VTFX"

# Step 1. Extract lzma data from the vtfx file
goto 0xc
get LZMA_OFF long

goto 0x14
get IMG_WIDTH short
get IMG_HEIGHT short

goto LZMA_OFF
endian little
getdstring LZMA 4
get SIZE long
get ZSIZE long
getdstring LZMA_PROP 5

get NAME basename
string NAME + ".textures"
comtype lzma_dynamic LZMA_PROP
savepos OFFSET
clog NAME OFFSET ZSIZE SIZE

# Step 2. Extract dds data from end of .textures file
Open . NAME 1
get SIZE_TEXTURES_FILE asize 1
XMath IMG_SIZE "(IMG_WIDTH * IMG_HEIGHT)"
XMath OFFSET_IMG "(SIZE_TEXTURES_FILE - IMG_SIZE)"
get NAME basename
string NAME + ".texture"
log NAME OFFSET_IMG IMG_SIZE 1

# Step 3. Byte-swap (big-endian -> little-endian) the .texture data
Open . NAME 2
xmath NUM_SHORTS "IMG_SIZE / 2"
for i = 0 < NUM_SHORTS
 encryption swap 2
next i
get NAME basename
string NAME + "_swp.texture"
log NAME 0x0 IMG_SIZE 2

# Step 4. Prepend a DXT5 DDS header
Open . NAME 3
encryption "" ""
set MEMORY_FILE binary "\x44\x44\x53\x20\x7c\x00..." # DDS "DDS " header
putVarChr MEMORY_FILE 0xc IMG_HEIGHT short
putVarChr MEMORY_FILE 0x10 IMG_WIDTH short
string NAME += ".dds"
get SIZE asize MEMORY_FILE
append
log NAME 0 SIZE MEMORY_FILE
log NAME 0 IMG_SIZE 3

Practical workflow (cfarl, 2017-12)

1. Use the BMS script to extract the LZMA data → .textures file.
2. Take the last width × height bytes (largest mip) as the image data.
3. Byte-swap back to little-endian.
4. Prepend a DXT5 DDS header.
5. To re-import: recompress with your own LZMA (QuickBMS reimport is unreliable — compressed size differs). (Acewell, cfarl, 2017-12-03)
6. Maintain the same image format, size, and mipmaps, and byte-swap back to big-endian after editing. (Acewell, 2017-12-02)
7. cfarl's fix for the "english shadow" (stale mipmaps): zero out all bytes before the DDS image so leftover mip data doesn't display. (cfarl, 2017-12-03)

Relevance: VTFX also applies to Portal: Still Alive on Xbox 360 (cfarl extracted howtoplay01.360.vtf for localization). Reference: Valve VTF spec — http://developer.valvesoftware.com/wiki/VTF

3. Xbox 360: 360.zip Archives

Topic 3258 (2008–2011). The Xbox 360 version of L4D stores all its files in 360.zip files. These cannot be extracted by normal zip tools even though the format looks identical to a standard zip. (TheGeneral, 2008-12-19)

• Tool: XZIP.rar extractor (TheGeneral) — works on the 360.zip files of Left 4 Dead and Portal: Still Alive.
• Rebuilding: rezip the files into an uncompressed zip archive and the game still loads everything. (TheGeneral, 2008-12-19)
• Gotcha: rebuilding must produce an uncompressed archive; compression breaks the injection (Frosty, 2009-06-15; adamharms, 2011-12-22).

4. Script/Data Encryption (Source SDK)

Topic 7964 (2011-2012). For Steam versions, the Source SDK includes a tool to encrypt/decrypt the .dat/.txt files. (qabRieL, 2012-01-02)

Tools Reference

Tool	Purpose	Author
Gibbed.Valve.ExtractPackage	VPK extraction (PC)	Rick (Gibbed)
XZIP	360.zip extraction (Xbox 360)	TheGeneral
QuickBMS + VTFX script	VTFX LZMA → DDS extraction	cfarl / Acewell
Source SDK	.dat/.txt encrypt/decrypt	Valve

Key Facts

• PC L4D uses .vpk archives (not .gcf).
• Xbox 360 L4D uses 360.zip archives and VTFX textures.
• VTFX = modified Valve VTF with LZMA-compressed payload, big-endian DXT5, inverted mip order (smallest first, largest last).
• VTFX header magic 0x56544658 ("VTFX"); image dims at 0x14/0x16; LZMA offset pointer at 0x0C.