FF7/Battle/Battle Scenes/Battle Script

(Information on opcodes provided by Terence Fergusson. Almost all information comes from this post on the forums.)

There are four actions to be explained when dealing with any opcode in AI script: Arguments, Values to take from the stack, what to do with Arguments and Values, and what to put back on the stack. So to fully understand what is happening a brief explanation of the stack is necessary.

The stack is more-or-less a list of values with different lengths. Only the top of the stack (the most recently added value) can be accessed at any given time, but when that value is accessed it is removed from the top of the stack and the previously added value now becomes the top of the stack. Adding to the stack is called "Pushing" a value and taking a value off is called "Popping". When pushing a value to the stack, the value of the number is pushed followed by the value type. The value type can be one of three different things:

Code	Type
0Xh	Value
1Xh	Address
2Xh	Multiple (between 1-10) Values

They are stored as DWords, but the X will determine how many bytes to use: 0 = bit, 1 = Byte, 2 = Word, 3 = Three bytes

Now that we've seen the stack, here are the opcodes:

Code	Arguments	Value(s) to pop	Value to push
Push Values
0Xh	2 byte Memory Address		Type 0X stored at translated Address
Push Addresses
1Xh	2 byte Memory Address		Address value with a scope of X
Mathematical and Bit-wise Operators
30h		Two of any type	Sum of pops
31h		Two of any type	Difference of pops
32h		Two of any type	Product of pops
33h		Two of any type	Quotient of pops
34h		Two of any type	Remainder from quotient of pops
35h		Two of any type	Bit-wise AND of pops
36h		Two of any type	Bit-wise OR of pops
37h		One of any type	Bit-wise NOT of pop
Logical Operators
40h		Two of any type	True if pops are EQUAL
41h		Two of any type	True if pops are NOT EQUAL
42h		Two of any type	True if first pop is GREATER THAN OR EQUAL TO second pop
43h		Two of any type	True if first pop is LESS THAN OR EQUAL TO second pop
44h		Two of any type	True if first pop is GREATER THAN second pop
45h		Two of any type	True if first pop is LESS THAN second pop
Logical Comparisons
50h		Two of any type	True if both pops are NON-ZERO (Logical AND)
51h		Two of any type	True if either pop is NON-ZERO (Logical OR)
52h		One of any type	True if pop is ZERO (Logical NOT)
Push Constants
60h	1 byte Value		Argument of type 01
61h	2 byte Value		Argument of type 02
62h	3 byte Value		Argument of type 03
Script Jumps (No Pushes)
70h	2 byte Script Address	One of any type	Jumps to script address in argument if pop is 0
71h	2 byte Script Address	One of any type	Jumps to script address in argument if pop and top of stack are not equal
72h	2 byte Script Address		Jumps to script address in argument
73h	This ends the script
74h		One of any type	Pops one value from stack. (Not used)
75h		One of any type	Link all scripts of script owner to popped Character ID.
Bit Operations
80h		Two of any type	First pop masked by second pop
81h			Random Word (0-65535)
82h		One of any type	Random bit of pop stored as type 02
83h		One of any type	Type 01 with count of number of bits set in pop
84h		One of type 2X	Type 02 indicating which values in popped set were greatest
85h		One of type 2X	Type 02 indicating which values in popped set were least
86h		One of type 1X	Type 02 indicating MP Cost of attack index referenced in pop
87h		One of any type	Type 02 with only bit in pop turned on (1 << [pop])

 

Command
Code	Arguments	Value(s) to pop	Effect
90h		One of type 1X, One of type 0X or 2X	If first pop < 4000h; Stores second pop at first pop
90h		One of type 1X, One of type 0X or 2X, One of type 1X	If first pop >= 4000h; Stores second pop at first pop constrained by mask at third pop
91h		One of any type	Pops one value from stack.
92h		Two of any type	First pop is attack ID to perform. Second pop action type
93h	NULL terminated string		Displays string
94h		Two of any type	Copy current status, hp and mp as well as some other specific data (like boosts, multipliers) from units in first given mask to units in second mask.
95h		One of type 1X, one of type 00	If second pop is 1, takes value at local address 2010 and writes value at memory bank 1/2 at offset specified by first pop If second pop is 0, data at memory bank1/2 at offset specified by first pop is stored at local address 2010. Otherwise, command is ignored.
96h		Two of any type	Get fighter elemental defense.
A0h	One byte, NULL terminated ASCII	First argument of any type	Displays string to debug console, replacing "%d"s with pops
A1h		Two values of any type	Pops two values from stack (Not Used, but valid command)

GENERAL NOTES:

• Command 90h is overloaded.
• If a type 2X is popped and any type is accepted, only the first value will be considered.
• If specific type is expected and that type is not available, the game with either crash or ignore that entire line.
• TRUE and FALSE are stored as type 00 as '1' and '0' respectively.
• Commands 74h and A1h are never used, but have been documented as valid commands.
• Commands 75h and 96h only appear in the Character AI found in the KERNEL.BIN.
• Commands of group 2X, BX, CX, DX, EX, and FX are treated as NOPs. The script will ignore them and continue processing. Also, any 5X, 6X, 7X, 8X, and 9X value that isn't listed above appear to be treated the same way, but it's safest to use a value from the 2X group. An incorrect 0X, 1X, 3X, or 4X will have unintended side-effects.

0X & 1X CODES NOTES:

• Valid values for X are 0, 1, 2, and 3.
  • These will store a bit, byte, word, and dword respectively.

3X CODES NOTES:

• The pushed value is type 2x if either of the pops are a 1X or 2X. In that case, the Masks of both pops are ANDed together. In *all* cases, the highest pop's size is used to determine the new pop's size.

4X CODES NOTES:

• The Pushed value will be type 00 if either component is a 1X or 2X type. It will only push TRUE or FALSE
• If both were 0X types, the result will be a type 02 which contains the Mask of all the objects in the pops that passed the comparison

86 CODE NOTES:

• This get the MP Cost of the ability referenced in the pop. The value of pop is referenced to the following areas:

 If Value >= 0xFFFF, return 0
 If Value <= 0x00FF, Addr = 00DAAC78 + Value*0x1C
 If Value >= 0x0100, match Value with wr[0099AAF4+(ID=[0..31])*2]
    First ID it matches, Addr = 0099A774 + ID*0x1C
 If no Addr is found, return 0
 Otherwise, return wr[Addr + 4]

The pushed value is, thus, the MP cost of the defined ability as a type 02. Note that 0x00 to 0xFF are standard magic and always loaded, while 0x100+ are the unique abilities loaded through scene.bin.

92 CODE NOTES:

• Second pop must be one of the following:

Command index in case of character AI

20h - For enemy attack

22h - Force execution of script (referenced by first pop)

24h - Pauses battle engine while string is displayed (in conjunction with code 93)