SCO

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SCO files contain GTA 4's game scripts. Its new format replaces old scm one.

File Format

A SCO file is layed out into 4 segments. First the Header containing information about the SCO file. Then the Code Segment which contains the opcode's which govern how the script behaves. The next segment is the Local Variable container which contains enough space to hold the local variables. The last is the Global Variable container, which contains enough space to house the global variables, as well as setting them by default.

Header

There are 2 types of SCO files, an encrypted and unencrypted one. Each file however shares the same unencrypted header structure, and you can use this to determine which type of SCO file you are dealing with. The size of this header is 24 bytes.

4b - CHAR[4]/UINT32 - SCO Identifier
4b - UINT32 - Code Size
4b - UINT32 - Local Var Size
4b - UINT32 - Global Var Size
4b - UINT32 - Script Flags
4b - UINT32 - Signature

The SCO Identifier will be "SCR\r" (or 0xD524353) in an unencrypted version, and "scr"+0xE (or 0xE726373) in an encrypted version. The Code Size refers to the amount of bytes the code section takes up. The Local Var Size refers to the amount of local variables the SCO file contains. The segment for local variables starts at the end of Header + Code Size, and continues for 4x the local variable size (due to the local variables being stored in 4 byte segments). The Global Var Size refers to the amount of global variables the SCO file contains. The segment for global variables starts at the end of Header + Code Size + Local Var Size * 4, and continues for 4x the global variable size (due to the global variables being stored in 4 byte segments). The Script Flags are boolean bits which are currently unexplained. The Signature only differs in navgen_main, but could possibly set the script priority.

Code Segment

The Code Segment contains the opcodes which govern the scripts behaviour.

Opcodes

Opcodes can have varying sizes, but all opcodes are identified by their first byte. There are 80 opcodes which can occur, any opcode above 80 is a Push opcode which pushes it's own number - 96 onto the stack.

ID Name Description Length
1 Add Adds the top 2 items on the stack 1 byte
2 Sub Subtracts the top 2 items on the stack 1 byte
3 Mul Multiplies the top 2 items on the stack 1 byte
4 Div Divides the top 2 items on the stack 1 byte
5 Mod Mods the top 2 items on the stack 1 byte
6 IsZero Checks the first item on the stack to see if it equals 0 1 byte
7 Neg Reverses the sign on the item on the top of the stack 1 byte
8 CmpEq Compares the top 2 integers on the stack to see if they are equal 1 byte
9 CmpNe Compares the top 2 integers on the stack to see if they are not equal 1 byte
10 CmpGt Compares the top 2 integers on the stack to see if the first one is greater than the second one 1 byte
11 CmpGe Compares the top 2 integers on the stack to see if the first one is greater than or equal to the second one 1 byte
12 CmpLt Compares the top 2 integers on the stack to see if the first one is less than the second one 1 byte
13 CmpLe Compares the top 2 integers on the stack to see if the first one is less than or equal to the second one 1 byte
14 AddF Adds the top 2 floats on the stack 1 byte
15 SubF Subtracts the top 2 floats on the stack 1 byte
16 MulF Multiplies the top 2 floats on the stack 1 byte
17 DivF Divides the top 2 floats on the stack 1 byte
18 ModF Mods the top 2 floats on the stack 1 byte
19 NegF Reverses the sign on the first float on the stack 1 byte
20 CmpEqF Compares the top 2 floats on the stack to see if they are equal 1 byte
21 CmpNeF Compares the top 2 floats on the stack to see if they are not equal 1 byte
22 CmpGtF Compares the top 2 floats on the stack to see if the first one is greater than the second one 1 byte
23 CmpGeF Compares the top 2 floats on the stack to see if the first one is greater than or equal to the second one 1 byte
24 CmpLtF Compares the top 2 floats on the stack to see if the first one is less than the second one 1 byte
25 CmpLeF Compares the top 2 floats on the stack to see if the first one is less than or equal to the second one 1 byte
26 AddVec Adds the top 2 Vectors on the stack 1 byte
27 SubVec Subtracts the top 2 Vectors on the stack 1 byte
28 MulVec Multiplies the top 2 Vectors on the stack 1 byte
29 DivVec Divides the top 2 Vectors on the stack 1 byte
30 NegVec Reverses the sign on the first vector on the stack 1 byte
31 And Performs an And operation to the first 2 integers on the stack 1 byte
32 Or Performs an Or operation to the first 2 integers on the stack 1 byte
33 Xor Performs a Xor operation to the first 2 integers on the stack 1 byte
34 Jump Jumps to a section of code, using the next 4 bytes after the opcode as a placement 5 bytes
35 JumpFalse Jumps to a section of code if the top of the stack is 0, using the next 4 bytes after the opcode as a placement 5 bytes
36 JumpTrue Jumps to a section of code if the top of the stack is 1, using the next 4 bytes after the opcode as a placement 5 bytes
37 ToF Converts the top integer on the stack to a float, and puts that float on the stack 1 byte
38 FromF Converts the top float on the stack to an integer, and puts that integer on the stack 1 byte
39 VecFromF Converts the top float into a Vector containing 3 instances of the same float, and pushes the pointer to that Vector onto the top of the stack 1 byte
40 PushS Pushes a short onto the stack, the short is defined in the next 2 bytes after the opcode 3 bytes

Note: The Vectors on the stack are pointers to the memory containing the full vector. This section is incomplete. You can help by fixing and expanding it.