Difference between revisions of "Type1"

Latest revision as of 21:02, 17 September 2012

[edit] Package File Format

This will be Broken into 3 parts. DATS/Holes/Records, Compression, and DIR files

[edit] Format of Simcity4 Archive data files

Most simcity Data is as you probably know stored in various types of archive files that all have the same internal format such as DAT, SC4, SC4lot, etc. This format is proprietary to maxis and has been used in the sims online as well as this one. Header (96 bytes) File 1 File 2 File n Index Entry 1 (20 bytes) Index Entry 2 Index Entry n

Header first, individual files following with no filenames and a small file header area at the beginning of each followed by an index of all the files in the archive at 20 bytes per entry.

Header:

Offset 00 - Identifier (DBPF - the type of dat) Offset 04 - Version Major (1 in SC4/Ts2 Dats) Offset 08 - Version Minor (0 in sc4 dats, 1 in most TS2 packages) Offset 12 - 3 DWORDS of unused data. RESERVED for maxis use. Offset 24 - Date Created in Hex (Unused in Version 1.1) Offset 28 - Date Modified in Hex (Unused in Version 1.1) Offset 32 - Index Type/Version (Always 7 in SC4/TS2 dats) Offset 36 - Number of entries in the index Offset 40 - Location of first index entry Offset 44 - Size of index Offset 48 - Number of Hole entries in the Hole Record Offset 52 - Location of the hole Record Offset 56 - Size of the hole Record Offset 60 - Unknown. (Version 1.1+ in TS2 only) Offset 64 - 32 Bytes reserved for Future Use in other versions.

File: (file may start at very beginning or file may start at an offset of 9 from here depending)

Offset 00 - Size of file Offset 04 - Compression signature (if file is compressed or not) Offset 06 - Uncompressed filesize Offset 09 - Start of compressed/uncompressed file data

The size of an index entry is 20 bytes, like this:

Offset 00 - Type ID (main type of file. picture, texture, model etc) Offset 04 - Group ID (group of the file by purpose or type) Offset 08 - Instance ID (marker used by the format for finding a specific file) Offset 12 - Location of the file in the archive Offset 16 - Size of the file

One of the problems with this dat format is that filenames and filetypes are not preserved. Therefore the only way of knowing the type of file is by its IDS and then you don't have a true extension. It is for this reason that some of the filetypes to follow have names created by us instead of the true Maxis names. They simply aren't available.

A Hole record contains the location and size of all holes in a DAt file. Its format is as follows

(repeating) DWORD - Hole Location DWORD - Hole size

a Hole is simply garbage data that can be filled in with useful data at a later point

[edit] Compression

The idea behind the compression is to reuse previously decoded strings. For example, if the word "heureka" occurs twice in a file, the second occurence would be encoded by pointing to the first.

The compression is done by defining control characters that tells three things:

• How many characters of plain text that follows that should be appended to the output.

2) How many characters that should be read from the already decoded text (and appended to the output) 3) At which offset in the aldready decoded text to read the characters.

Thus, the algorithm to decompress these files goes like this:

Read file size at offset 0 Seek to offset 9 while not end of file is reached do { - Read next control character. - (Depending on control character read 0-3 more bytes that are a part of the control character.) - Figure out how many characters that should be read and from where by inspecting the control character. - Read 0-n characters from source and append them to the output. - Copy 0-n characters from somewhere in the output to the end of the output. }

There are 4 types of control characters which are used with different restrictions of how many characters that can be read and from how far behind these can be read. The following conventions are used to describe them:

CC length - Length of control character. Num plain text - Number of chars immediately after the control character that should be read and appended to output. Num to copy - Number of chars that should be copied from somewhere in the already decoded output and added to the end of the output. Copy offset - Where to start reading characters when copying from somewhere in the already decoded output. This is given as an offset from the current end of the output buffer, i.e. an offset of 0 means that you should copy the last character in the output and append it to the output. And offset of 1 means that you should copy the second-to-last character. byte0 - first byte of control character. Bits - Bits of the control character. p = num plain text, c = num to copy, o = copy offset, i = identifier.

Note: It can sometimes be confusing when a control character states that you should copy for example 10 characters 5 steps from the end of the output. Clearly, you cannot read more than 5 characters before you reach the end of the buffer. The solution is to read and write one character at the time. Each time you read a character you copy it to the end thereby increasing the size of the output. By doing this, even offset 0 is possible and would result in duplicating the last character a number of times. This is utilized by the compression to recreate repeating text, for example bars of repeating dashes

0xE0 - 0xFF

CC length: 1 byte Num plain text: (byte0 - 0xDF) < < 2 Num to copy: 0 Copy offset: -

Bits: 111ppppp Num plain text limit: 4-200 Num to copy limit: 0 Maximum Offset: -

This is the simplest form of control character. The only thing it does is telling how many plain text characters that follows. The formula for this is: (C - 0x7F) * 4. Thus a value of 0xE0 means that you should read 4 characters of plain text and append to the output.

0x00 - 0x7F

CC length: 2 bytes Num plain text: byte0 & 0x03 Num to copy: ( (byte0 & 0x1C) > > 2) + 3 Copy offset: ( (byte0 & 0x60) < < 3) + byte1

Bits: 0oocccpp oooooooo Num plain text limit: 0-3 Num to copy limit: 3-11 Maximum Offset: 1023

0x80 - 0xBF

CC length: 3 bytes Num plain text: (byte1 & 0xC0) > > 6 Num to copy: (byte0 & 0x3F) + 4 Copy offset: ( (byte1 & 0x3F) < < + byte2

Bits: 10cccccc ppoooooo oooooooo

Num plain text limit: 0-3 Num to copy limit: 4-67 Maximum Offset: 16383

0xC0 - 0xDF

CC length: 4 bytes Num plain text: byte0 & 0x03 Num to copy: ( (byte0 & 0x1C) < < + byte3 + 5 Copy offset: (byte1 < < + byte2

Bits: 110cccpp oooooooo oooooooo cccccccc

Num plain text limit: 0-3 Num to copy limit: 5-2047 Maximum Offset: 65535

[edit] Directory Files explained

Directory files are one of the newer filetypes I found about the beginning of May. Their purpose is to spead up the loading of a DAT file by showing exactly what is compressed inside it. They are directories of all the compressed files in an archive. This luckily makes their structure fairly simple. 4 DWORDS repeated over and over

(Repeated Chunk)

DWORD - Type ID of the file DWORD - Group ID of the file DWORD - Instance ID of the file DWORD - Size of the decompressed file in Hex

These files are found as DIR/Directory by the reader and are automatically modified by it during changes to dat files.

It is HIGHLY reccommended that you modify the Directory after editing any compressed file before saving the dat if you are working manually in Hex or making your own program.

If identifying Directory files manually by Hex, their Type ID in the index will be (EF 1E 6B E8)