FF7/Battle/Battle Scenes/Battle Script

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Revision as of 20:46, 2 December 2008 by my_wiki>Akari

(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 can be accessed at any given time, but when that value is accessed it leaves 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 = DWord

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 Address Type 0X stored at translated Address
Push Addresses
1Xh 2 byte Address Argument Type 1X
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 One Byte Argument of type 01
61h Two Bytes Argument of type 02
62h Four Bytes Argument of type 03
Script Jumps
70h Two Bytes One of any type Jumps to script address in argument if pop is 0
71h Two Bytes One of any type Jumps to script address in argument if pop and top of stack are not equal
72h Two Bytes Jumps to script address in argument
73h This ends the script
74h One of any type
75h One of any type Link all scripts of this fighter to given fighter.
Bit Operations
80h One of type 0X or 2X, One of any type First pop ANDed with 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])
Commands 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 variable from stack.
92h Two of any type First pop is attack ID to perform. Second pop action type (0x20 - enemy attack or 0x24 - display string)
93h NULL terminated string Displays string
94h Two of any type
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 bank1/2, get data to 2010 from memory bank1/2 otherwise.
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 ? ? ?


GENERAL NOTES:

  • Commands 90h and 95h are 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.

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.