Difference between revisions of "SCM Instruction"

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Each instruction is comprised of an ''opcode'' and ''arguments''.
 
Each instruction is comprised of an ''opcode'' and ''arguments''.
*The "opcode" (short for "[[Wikipedia:Opcode|operation code]]") is a number that tells the game which operation to perform. For example, the opcode [[0001]] tells the game to wait for a certain amount of time, [[0003]] shakes the game camera and [[0053]] creates a player. The opcode is a [[Wikipedia:UINT16|16 bit unsigned integer]].
+
*The "opcode" (short for "[[Wikipedia:Opcode|operation code]]") is a number that tells the game which operation to perform. For example, the opcode [[0001]] tells the game to wait for a certain amount of time, [[0003]] shakes the game camera and [[0053]] creates a player. The opcode is a signed 16-bit integer.
 
*"Arguments" are values sent with the instruction to change what it does. For example, you can change the amount of time to wait when using opcode [[0001]] by sending a different argument.
 
*"Arguments" are values sent with the instruction to change what it does. For example, you can change the amount of time to wait when using opcode [[0001]] by sending a different argument.
  
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While the opcode bytes are always present, there may not always be arguments passed, so there may be no argument bytes.
 
While the opcode bytes are always present, there may not always be arguments passed, so there may be no argument bytes.
  
Although an unsigned 16-bit integer (<code>uint16</code>) can hold values in the range <code>0x0000</code> - <code>0xFFFF</code>, the range of used opcodes in unmodded games is much smaller. For example, [[San Andreas]] has opcodes going up to <code>0x0A4E</code>. There are tools that add more instructions to the game, most notably the [[CLEO|CLEO Library]].  
+
No GTA game uses all the available opcodes (32,767 or <code>0x7FFF</code>). There are mods that add more instructions to the game, most notably the [[CLEO|CLEO Library]].
  
Any values over the ''signed'' 16-bit integer maximum value (<code>0x7FFF</code>) denote negative [[Conditional statement|conditional opcodes]], which suggests that the opcodes are not always treated as unsigned integers by the game.
+
Although opcodes are typically considered as being two bytes long and thus 16 bits, actual opcodes only ever use 15 of those bits. This is because the most significant bit (<code>0x8000</code>) is reserved for use in compiled code as a way of telling the runtime to invert the return value of an operation. For example, <code>IS_CHAR_DEAD</code> has opcode <code>[[0118|0x118]]</code> (<code>0b100011000</code>) and is used to find out if a given actor is dead. If a script wants to find if a character is <i>not</i> dead, the written opcode would be <code>0x8118</code> (<code>0b1000000100011000</code>), as the <code>0x8000</code> bit is set to 1 to invert the result. The inversion bit can be masked off by ANDing the written opcode with <code>0x7fff</code> (<code>op & 0x7fff</code>).
  
 
== Arguments ==
 
== Arguments ==
Line 55: Line 55:
 
!Support
 
!Support
 
!Description&nbsp;
 
!Description&nbsp;
 +
|-
 +
!colspan=6|Typified
 
|-
 
|-
 
|-valign="top"
 
|-valign="top"
Line 60: Line 62:
 
|-valign="top"
 
|-valign="top"
 
|01||4||{{icon|3}} {{icon|vc}} {{icon|sa}}||Immediate 32-bit signed int
 
|01||4||{{icon|3}} {{icon|vc}} {{icon|sa}}||Immediate 32-bit signed int
<source lang="cpp">scriptParam.m_iIntValue = *(int *)m_pScriptPC;
+
value = ReadInt32(Bytecode, PC)
m_pScriptPC += 4;</source>
+
PC += 4
 
|-valign="top"
 
|-valign="top"
|02||2||{{icon|3}} {{icon|vc}} {{icon|sa}}||Global integer/floating-point variable
+
|{{anchor|globaltri}}02||2||{{icon|3}} {{icon|vc}} {{icon|sa}}||Global integer/floating-point variable (offset)
<source lang="cpp">scriptParam.m_usGlobalOffset = *(unsigned short *)m_pScriptPC;
+
globalVar = ReadUInt16(Bytecode, PC)
m_pScriptPC += 2;</source>
+
PC += 2
 
|-valign="top"
 
|-valign="top"
|03||2||{{icon|3}} {{icon|vc}} {{icon|sa}}||Local integer/floating-point variable
+
|{{anchor|localtri}}03||2||{{icon|3}} {{icon|vc}} {{icon|sa}}||Local integer/floating-point variable (index)
<source lang="cpp">scriptParam.m_sLocalVar = *(short *)m_pScriptPC;
+
localVar = ReadUInt16(Bytecode, PC)
m_pScriptPC += 2;</source>
+
PC += 2
 
|-valign="top"
 
|-valign="top"
 
|04||1||{{icon|3}} {{icon|vc}} {{icon|sa}}||Immediate 8-bit signed int
 
|04||1||{{icon|3}} {{icon|vc}} {{icon|sa}}||Immediate 8-bit signed int
<source lang="cpp">scriptParam.m_iIntValue = *(char *)m_pScriptPC++;</source>
+
value = SignExtend32(ReadInt8(Bytecode, PC))
 +
PC += 1
 
|-valign="top"
 
|-valign="top"
 
|05||2||{{icon|3}} {{icon|vc}} {{icon|sa}}||Immediate 16-bit signed int
 
|05||2||{{icon|3}} {{icon|vc}} {{icon|sa}}||Immediate 16-bit signed int
<source lang="cpp">scriptParam.m_iIntValue = *(short *)m_pScriptPC;
+
value = SignExtend32(ReadInt16(Bytecode, PC))
m_pScriptPC += 2;</source>
+
PC += 2
 
|-valign="top"
 
|-valign="top"
 
|06||2||{{icon|3}}||Immediate 16-bit fixed-point (see [[Talk:Mission_Scripting_(Overview)#Fixed-point_remark|remark]])
 
|06||2||{{icon|3}}||Immediate 16-bit fixed-point (see [[Talk:Mission_Scripting_(Overview)#Fixed-point_remark|remark]])
<source lang="cpp">scriptParam.m_fFloatValue = (float)(*(short *)m_pScriptPC) / 16.0f;
+
value = ToFloat32(ReadUInt16(Bytecode, PC)) / 16.0
m_pScriptPC += 2;</source>
+
PC += 2
 
|-valign="top"
 
|-valign="top"
 
|06||4||align="right"|{{icon|vc}} {{icon|sa}}||Immediate 32-bit floating-point
 
|06||4||align="right"|{{icon|vc}} {{icon|sa}}||Immediate 32-bit floating-point
<source lang="cpp">scriptParam.m_fFloatValue = *(float *)m_pScriptPC;
+
value = ReadFloat32(Bytecode, PC)
m_pScriptPC += 4;</source>
+
PC += 4
 
|-valign="top"
 
|-valign="top"
|07||6||align="right"|{{icon|sa}}||Global integer/floating-point array{{ref|varray|[*]}}
+
|{{anchor|globaltri2}}07||6||align="right"|{{icon|sa}}||Global integer/floating-point array (offset)
<source lang="cpp">scriptParam.m_usGlobalOffset = *(unsigned short *)m_pScriptPC;
+
globalVar = ReadUInt16(Bytecode, PC)
scriptParam.m_sArrayIndexVar = *(short *)(m_pScriptPC + 2);
+
arrayIndexVar = ReadUInt16(Bytecode, PC+2)
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 4);
+
//arraySize = ReadUInt8(Bytecode, PC+4)
scriptParam.m_arrayProperties = *(ArrayProperties *)(m_pScriptPC + 5);
+
//elementType = ReadUInt8(Bytecode, PC+5) & 0x7F
m_pScriptPC += 6;</source>
+
isGlobalIndex = ReadUInt8(Bytecode, PC+5) >> 7
 +
PC += 6
 
|-valign="top"
 
|-valign="top"
|08||6||align="right"|{{icon|sa}}||Local integer/floating-point array{{ref|varray|[*]}}
+
|{{anchor|localtri2}}08||6||align="right"|{{icon|sa}}||Local integer/floating-point array (index)
<source lang="cpp">scriptParam.m_sLocalVar = *(short *)m_pScriptPC;
+
localVar = ReadUInt16(Bytecode, PC)
scriptParam.m_sArrayIndexVar = *(short *)(m_pScriptPC + 2);
+
arrayIndexVar = ReadUInt16(Bytecode, PC+2)
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 4);
+
//arraySize = ReadUInt8(Bytecode, PC+4)
scriptParam.m_arrayProperties = *(ArrayProperties *)(m_pScriptPC + 5);
+
//elementType = ReadUInt8(Bytecode, PC+5) & 0x7F
m_pScriptPC += 6;</source>
+
isGlobalIndex = ReadUInt8(Bytecode, PC+5) >> 7
 +
PC += 6
 +
|-
 +
!colspan=6|Typified (strings)
 
|-valign="top"
 
|-valign="top"
|09||8||align="right"|{{icon|sa}}||Immediate 8-byte string{{ref|str8|[*]}}
+
|09||8||align="right"|{{icon|sa}}||Immediate 8-byte string
<source lang="cpp">strcpy(scriptParam.m_szTextLabel, (char *)m_pScriptPC);
+
textLabel = ReadString(Bytecode, PC, 8)
m_pScriptPC += 8;</source>
+
PC += 8
 
|-valign="top"
 
|-valign="top"
|0A||2||align="right"|{{icon|sa}}||Global 8-byte string variable
+
|0A||2||align="right"|{{icon|sa}}||Global 8-byte string variable (see [[#globaltri|02]])
<source lang="cpp">scriptParam.m_usGlobalOffset = *(unsigned short *)m_pScriptPC;
 
m_pScriptPC += 2;</source>
 
 
|-valign="top"
 
|-valign="top"
|0B||2||align="right"|{{icon|sa}}||Local 8-byte string variable
+
|0B||2||align="right"|{{icon|sa}}||Local 8-byte string variable (see [[#localtri|03]])
<source lang="cpp">scriptParam.m_sLocalVar = *(short *)m_pScriptPC;
 
m_pScriptPC += 2;</source>
 
 
|-valign="top"
 
|-valign="top"
|0C||6||align="right"|{{icon|sa}}||Global 8-byte string array{{ref|varray|[*]}}
+
|0C||6||align="right"|{{icon|sa}}||Global 8-byte string array (see [[#globaltri2|07]])
<source lang="cpp">scriptParam.m_usGlobalOffset = *(unsigned short *)m_pScriptPC;
 
scriptParam.m_sArrayIndexVar = *(short *)(m_pScriptPC + 2);
 
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 4);
 
scriptParam.m_arrayProperties = *(ArrayProperties *)(m_pScriptPC + 5);
 
m_pScriptPC += 6;</source>
 
 
|-valign="top"
 
|-valign="top"
|0D||6||align="right"|{{icon|sa}}||Local 8-byte string array{{ref|varray|[*]}}
+
|0D||6||align="right"|{{icon|sa}}||Local 8-byte string array (see [[#localtri2|08]])
<source lang="cpp">scriptParam.m_sLocalVar = *(short *)m_pScriptPC;
 
scriptParam.m_sArrayIndexVar = *(short *)(m_pScriptPC + 2);
 
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 4);
 
scriptParam.m_arrayProperties = *(ArrayProperties *)(m_pScriptPC + 5);
 
m_pScriptPC += 6;</source>
 
 
|-valign="top"
 
|-valign="top"
|0E||1 + (n - 1)||align="right"|{{icon|sa}}||Immediate variable-length string{{ref|str16|[*]}} (non null-terminated)
+
|0E||1+n||align="right"|{{icon|sa}}||Immediate variable-length string (non null-terminated)
<source lang="cpp">char cStrLength = *(char *)m_pScriptPC++;
+
length = ReadInt8(Bytecode, PC)
strncpy(scriptParam.m_szTextLabel, (char *)m_pScriptPC, cStrLength);
+
textLabel = ReadString(Bytecode, PC+1, length)
memset(&scriptParam.m_szTextLabel[cStrLength], '\0', ucMaxLength - cStrLength);
+
          + StrPad("\0", 40-length)
m_pScriptPC += cStrLength;</source>
+
PC += 1+length
 
|-valign="top"
 
|-valign="top"
|0F||16||align="right"|{{icon|sa}}||Immediate 16-byte string{{ref|sa16|[*]}}
+
|0F||16||align="right"|{{icon|sa}}||Immediate 16-byte string
<source lang="cpp">strcpy(scriptParam.m_szTextLabel, (char *)m_pScriptPC);
+
textLabel = ReadString(Bytecode, PC, 16)
m_pScriptPC += 16;</source>
+
PC += 16
 
|-valign="top"
 
|-valign="top"
|10||2||align="right"|{{icon|sa}}||Global 16-byte string variable
+
|10||2||align="right"|{{icon|sa}}||Global 16-byte string variable (see [[#globaltri|02]])
<source lang="cpp">scriptParam.m_usGlobalOffset = *(unsigned short *)m_pScriptPC;
 
m_pScriptPC += 2;</source>
 
 
|-valign="top"
 
|-valign="top"
|11||2||align="right"|{{icon|sa}}||Local 16-byte string variable
+
|11||2||align="right"|{{icon|sa}}||Local 16-byte string variable (see [[#localtri|03]])
<source lang="cpp">scriptParam.m_sLocalVar = *(short *)m_pScriptPC;
 
m_pScriptPC += 2;</source>
 
 
|-valign="top"
 
|-valign="top"
|12||6||align="right"|{{icon|sa}}||Global 16-byte string array{{ref|varray|[*]}}
+
|12||6||align="right"|{{icon|sa}}||Global 16-byte string array (see [[#globaltri2|07]])
<source lang="cpp">scriptParam.m_usGlobalOffset = *(unsigned short *)m_pScriptPC;
 
scriptParam.m_sArrayIndexVar = *(short *)(m_pScriptPC + 2);
 
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 4);
 
scriptParam.m_arrayProperties = *(ArrayProperties *)(m_pScriptPC + 5);
 
m_pScriptPC += 6;</source>
 
 
|-valign="top"
 
|-valign="top"
|13||6||align="right"|{{icon|sa}}||Local 16-byte string array{{ref|varray|[*]}}
+
|13||6||align="right"|{{icon|sa}}||Local 16-byte string array (see [[#localtri2|08]])
<source lang="cpp">scriptParam.m_sLocalVar = *(short *)m_pScriptPC;
 
scriptParam.m_sArrayIndexVar = *(short *)(m_pScriptPC + 2);
 
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 4);
 
scriptParam.m_arrayProperties = *(ArrayProperties *)(m_pScriptPC + 5);
 
m_pScriptPC += 6;</source>
 
 
|-
 
|-
!colspan=6|No type code
+
!colspan=6|Untypified
 
|-valign="top"
 
|-valign="top"
 
|N/A||8||{{icon|3}} {{icon|vc}}||Immediate 8-byte string{{ref|vcstr|[*]}}
 
|N/A||8||{{icon|3}} {{icon|vc}}||Immediate 8-byte string{{ref|vcstr|[*]}}
<source lang="cpp">strcpy(scriptParam.m_szTextLabel, (char *)m_pScriptPC);
+
textLabel = ReadString(Bytecode, PC, 8)
m_pScriptPC += 8;</source>
+
PC += 8
 
|-valign="top"
 
|-valign="top"
 
|N/A||128||align="right"|{{icon|sa}}||Immediate 128-byte string
 
|N/A||128||align="right"|{{icon|sa}}||Immediate 128-byte string
<source lang="cpp">strcpy(scriptParam.m_szString, (char *)m_pScriptPC);
+
string = ReadString(Bytecode, PC, 128)
m_pScriptPC += 128;</source>
+
PC += 128
 
|}
 
|}
 
* In San Andreas, local and global variables are equivalent once interpreted by the game, so either may be passed to an instruction that expects one. The only difference between the two is where the value is stored internally, and this makes no difference to how an instruction executes: it will receive a raw pointer which is treated the same way regardless of type.
 
  
 
==== LCS/VCS ====
 
==== LCS/VCS ====
Line 190: Line 167:
 
|-valign="top"
 
|-valign="top"
 
|01||0||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 8-bit signed integer constant 0
 
|01||0||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 8-bit signed integer constant 0
<source lang="cpp">scriptParam.m_iIntValue = 0;</source>
+
value = 0
 
|-valign="top"
 
|-valign="top"
 
|02||0||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 8-bit floating-point constant 0.0
 
|02||0||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 8-bit floating-point constant 0.0
<source lang="cpp">scriptParam.m_fFloatValue = 0.0f;</source>
+
value = 0.0
 
|-valign="top"
 
|-valign="top"
 
|03||1||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 8-bit packed floating-point
 
|03||1||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 8-bit packed floating-point
<source lang="cpp">unsigned int uiUnpackedFloat = *(unsigned char *)m_pScriptPC++ << 24;
+
value = AsFloat32(ReadUInt8(Bytecode, PC) << 24)
scriptParam.m_fFloatValue = *(float *)&uiUnpackedFloat;</source>
+
PC += 1
 
|-valign="top"
 
|-valign="top"
 
|04||2||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 16-bit packed floating-point
 
|04||2||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 16-bit packed floating-point
<source lang="cpp">unsigned int uiUnpackedFloat = *(unsigned short *)m_pScriptPC << 16;
+
value = AsFloat32((ReadUInt8(Bytecode, PC) << 16)
scriptParam.m_fFloatValue = *(float *)&uiUnpackedFloat;
+
                <nowiki>|</nowiki> (ReadUInt8(Bytecode, PC+1) << 24))
m_pScriptPC += 2;</source>
+
PC += 2
 
|-valign="top"
 
|-valign="top"
 
|05||3||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 24-bit packed floating-point
 
|05||3||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 24-bit packed floating-point
<source lang="cpp">unsigned int uiUnpackedFloat
+
value = AsFloat32((ReadUInt8(Bytecode, PC) << 8)
    = (*(unsigned short *)m_pScriptPC << 16)
+
                <nowiki>|</nowiki> (ReadUInt8(Bytecode, PC+1) << 16)
    | (*(unsigned char *)(m_pScriptPC + 2) << 8);
+
                <nowiki>|</nowiki> (ReadUInt8(Bytecode, PC+2) << 24))
scriptParam.m_fFloatValue = *(float *)&uiUnpackedFloat;
+
PC += 3
m_pScriptPC += 3;</source>
 
 
|-valign="top"
 
|-valign="top"
 
|06||4||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 32-bit signed integer
 
|06||4||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 32-bit signed integer
<source lang="cpp">scriptParam.m_iIntValue = *(int *)m_pScriptPC;
+
value = ReadInt32(Bytecode, PC)
m_pScriptPC += 4;</source>
+
PC += 4
 
|-valign="top"
 
|-valign="top"
 
|07||1||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 8-bit signed integer
 
|07||1||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 8-bit signed integer
<source lang="cpp">scriptParam.m_iIntValue = *(char *)m_pScriptPC++;</source>
+
value = SignExtend32(ReadInt8(Bytecode, PC))
 +
PC += 1
 
|-valign="top"
 
|-valign="top"
 
|08||2||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 16-bit signed integer
 
|08||2||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 16-bit signed integer
<source lang="cpp">scriptParam.m_iIntValue = *(short *)m_pScriptPC;
+
value = SignExtend32(ReadInt16(Bytecode, PC))
m_pScriptPC += 2;</source>
+
PC += 2
 
|-valign="top"
 
|-valign="top"
 
|09||4||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 32-bit floating-point
 
|09||4||align="center"|{{icon|lcs}} {{icon|vcs}}||Immediate 32-bit floating-point
<source lang="cpp">scriptParam.m_fFloatValue = *(float *)m_pScriptPC;
+
value = ReadFloat32(Bytecode, PC)
m_pScriptPC += 4;</source>
+
PC += 4
 
|-valign="top"
 
|-valign="top"
|0A||n + NUL||align="right"|{{icon|vcs}}||Immediate null-terminated string{{ref|strvcs|[*]}}
+
|0A||n+NUL||align="right"|{{icon|vcs}}||Immediate null-terminated string{{ref|strvcs|[*]}}
<source lang="cpp">strcpy(scriptParam.m_szTextLabel, (char *)m_pScriptPC);
+
textLabel = ReadString(Bytecode, PC)
m_pScriptPC += strlen((char *)m_pScriptPC) + 1;</source>
+
PC += StrLen(textLabel)+1
 
|-
 
|-
!colspan=5|Untypified (script variables)
+
!colspan=5|Typified (script variables)
 
|-valign="top"
 
|-valign="top"
 
|0A..0B||1||{{icon|lcs}}||Local timers (''TIMERA'', ''TIMERB'')
 
|0A..0B||1||{{icon|lcs}}||Local timers (''TIMERA'', ''TIMERB'')
<source lang="cpp">scriptParam.m_sLocalVar = *(unsigned char *)m_pScriptPC++ + 0x5E;</source>
+
localVar = ReadUInt8(Bytecode, PC) + 0x5E
 +
PC += 1
 
|-valign="top"
 
|-valign="top"
 
|0B..0C||1||align="right"|{{icon|vcs}}||Local timers (''TIMERA'', ''TIMERB'')
 
|0B..0C||1||align="right"|{{icon|vcs}}||Local timers (''TIMERA'', ''TIMERB'')
<source lang="cpp">scriptParam.m_sLocalVar = *(unsigned char *)m_pScriptPC++ + 0x5D;</source>
+
localVar = ReadUInt8(Bytecode, PC) + 0x5D
 +
PC += 1
 
|-valign="top"
 
|-valign="top"
 
|0C..6B||1||{{icon|lcs}}||Local integer/floating-point variable
 
|0C..6B||1||{{icon|lcs}}||Local integer/floating-point variable
<source lang="cpp">scriptParam.m_sLocalVar = *(unsigned char *)m_pScriptPC++ - 0x0C;</source>
+
localVar = ReadUInt8(Bytecode, PC) - 0x0C
 +
PC += 1
 
|-valign="top"
 
|-valign="top"
 
|0D..6C||1||align="right"|{{icon|vcs}}||Local integer/floating-point variable
 
|0D..6C||1||align="right"|{{icon|vcs}}||Local integer/floating-point variable
<source lang="cpp">scriptParam.m_sLocalVar = *(unsigned char *)m_pScriptPC++ - 0x0D;</source>
+
localVar = ReadUInt8(Bytecode, PC) - 0x0D
 +
PC += 1
 
|-valign="top"
 
|-valign="top"
 
|6C..CB||3||{{icon|lcs}}||Local integer/floating-point array
 
|6C..CB||3||{{icon|lcs}}||Local integer/floating-point array
<source lang="cpp">scriptParam.m_sLocalVar = *(unsigned char *)m_pScriptPC - 0x6C;
+
localVar = ReadUInt8(Bytecode, PC) - 0x6C
scriptParam.m_sArrayIndex = *(unsigned char *)(m_pScriptPC + 2);
+
arrayIndexVar = ReadUInt8(Bytecode, PC+1)
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 3);
+
arraySize = ReadUInt8(Bytecode, PC+2)
m_pScriptPC += 3;</source>
+
PC += 3
 
|-valign="top"
 
|-valign="top"
 
|6D..CC||3||align="right"|{{icon|vcs}}||Local integer/floating-point array
 
|6D..CC||3||align="right"|{{icon|vcs}}||Local integer/floating-point array
<source lang="cpp">scriptParam.m_sLocalVar = *(unsigned char *)m_pScriptPC - 0x6D;
+
localVar = ReadUInt8(Bytecode, PC) - 0x6D
scriptParam.m_sArrayIndex = *(unsigned char *)(m_pScriptPC + 2);
+
arrayIndexVar = ReadUInt8(Bytecode, PC+1)
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 3);
+
arraySize = ReadUInt8(Bytecode, PC+2)
m_pScriptPC += 3;</source>
+
PC += 3
 
|-valign="top"
 
|-valign="top"
 
|CC..E5||2||{{icon|lcs}}||Global integer/floating-point variable{{ref|gvars|[*]}}
 
|CC..E5||2||{{icon|lcs}}||Global integer/floating-point variable{{ref|gvars|[*]}}
<source lang="cpp">unsigned short usBigEndianWord = *(unsigned short *)m_pScriptPC - 0x00CC;
+
globalVar = ByteSwap16(ReadUInt16(Bytecode, PC) - 0xCC)
scriptParam.m_sGlobalVar = (short)((usBigEndianWord << 8) | (usBigEndianWord >> 8));
+
PC += 2
m_pScriptPC += 2;</source>
 
 
|-valign="top"
 
|-valign="top"
 
|CD..E5||2||align="right"|{{icon|vcs}}||Global integer/floating-point variable{{ref|gvars|[*]}}
 
|CD..E5||2||align="right"|{{icon|vcs}}||Global integer/floating-point variable{{ref|gvars|[*]}}
<source lang="cpp">unsigned short usBigEndianWord = *(unsigned short *)m_pScriptPC - 0x00CD;
+
globalVar = ByteSwap16(ReadUInt16(Bytecode, PC) - 0xCD)
scriptParam.m_sGlobalVar = (short)((usBigEndianWord << 8) | (usBigEndianWord >> 8));
+
PC += 2
m_pScriptPC += 2;</source>
 
 
|-valign="top"
 
|-valign="top"
 
|E6..FF||4||align="center"|{{icon|lcs}} {{icon|vcs}}||Global integer/floating-point array
 
|E6..FF||4||align="center"|{{icon|lcs}} {{icon|vcs}}||Global integer/floating-point array
<source lang="cpp">unsigned short usBigEndianWord = *(unsigned short *)m_pScriptPC - 0x00E6;
+
globalVar = ByteSwap16(ReadUInt16(Bytecode, PC) - 0xE6)
scriptParam.m_sGlobalVar = (short)((usBigEndianWord << 8) | (usBigEndianWord >> 8));
+
arrayIndexVar = ReadUInt8(Bytecode, PC+2)
scriptParam.m_sArrayIndex = *(unsigned char *)(m_pScriptPC + 2);
+
arraySize = ReadUInt8(Bytecode, PC+3)
scriptParam.m_ucArraySize = *(unsigned char *)(m_pScriptPC + 3);
+
PC += 4
m_pScriptPC += 4;</source>
+
|-
 +
!colspan=6|Untypified
 
|-valign="top"
 
|-valign="top"
 
|N/A||8||{{icon|lcs}}||Immediate 8-byte string
 
|N/A||8||{{icon|lcs}}||Immediate 8-byte string
<source lang="cpp">strcpy(scriptParam.m_szTextLabel, (char *)m_pScriptPC);
+
textLabel = ReadString(Bytecode, PC, 8)
m_pScriptPC += 8;</source>
+
PC += 8
 
|}
 
|}
  
 
{{note|strvcs}} This type was introduced in VCS due to the presence of string variables.
 
{{note|strvcs}} This type was introduced in VCS due to the presence of string variables.
  
{{note|gvars}} Given the data type range limit the largest global variable in LCS is <code style="color:blue">$6655</code>, in VCS <code style="color:blue">$6399</code>.
+
{{note|gvars}} Given the data type range limit the largest global variable in LCS is 6655, in VCS is 6399.
  
 
=== Integer numbers ===
 
=== Integer numbers ===
Line 312: Line 292:
 
There are two kinds of string:
 
There are two kinds of string:
 
* Fixed-length. This is the most common type of string and has been used since [[GTA 3]]. The string length is fixed. When compiled these strings occupy a certain number of bytes (8 or 16) even if the text is actually shorter (any unused bytes are filled with [[Wikipedia:null terminator|null values]]).
 
* Fixed-length. This is the most common type of string and has been used since [[GTA 3]]. The string length is fixed. When compiled these strings occupy a certain number of bytes (8 or 16) even if the text is actually shorter (any unused bytes are filled with [[Wikipedia:null terminator|null values]]).
* Variable length (SA only). Variable-length strings are encoded as a single byte specifying the length followed by the string character bytes. These strings are not null-terminated. The maximum length depends on the instruction{{Ref|longstringslimits|[*]}}. The longest in the original game is 40 characters.
+
* Variable-length (SA only). Variable-length strings are encoded as a single byte specifying the length followed by the string character bytes. These strings are not null-terminated. The maximum length depends on the instruction{{Ref|longstringslimits|[*]}}. The longest in the original game is 40 characters.
  
 
{|{{Prettytable}}
 
{|{{Prettytable}}
Line 328: Line 308:
  
 
=== Arrays ===
 
=== Arrays ===
In GTA SA, an array is a static reference to a group of successive variables. There is no actual representation of an array ''value'' as a concrete type, they do have type codes. When an "array" is passed as an argument to an instruction, what is actually passed is a specific variable in that array.
+
In GTA SA, an array is a static reference to a group of successive variables. There is no actual representation of an array ''value'' as a concrete type, they do have type codes. When an "array" is passed as an argument to an instruction, what is actually passed is a specific variable in that array. For this reason, array elements are passed as variables of the type in the array – that is to say, a value from an array of global integer variables would be passed as a global integer variable. The game simply performs the extra step of retrieving the variable from the array before using it in the instruction.
  
 
This section describes the format of array accesses in GTA SA. Vice City also has arrays, but [[VC_Arrays|in a different format]].
 
This section describes the format of array accesses in GTA SA. Vice City also has arrays, but [[VC_Arrays|in a different format]].
  
 
<source lang="cpp">
 
<source lang="cpp">
// Example: not real code.
+
// Example; not real code.
 
// Applies only to GTA: SA.
 
// Applies only to GTA: SA.
 
struct ArrayAccess {
 
struct ArrayAccess {
Line 363: Line 343:
  
 
The array offset is a variable which should have a value more than or equal to 0 and smaller than the array size. Global and local variables can be used as index variables – the purpose of the <code>globalIndex</code> field is to tell the game which has been used. The first element in the array is at index <code>0</code>, and the last is at <code>length - 1</code>.
 
The array offset is a variable which should have a value more than or equal to 0 and smaller than the array size. Global and local variables can be used as index variables – the purpose of the <code>globalIndex</code> field is to tell the game which has been used. The first element in the array is at index <code>0</code>, and the last is at <code>length - 1</code>.
 
{|{{Prettytable}}
 
!width="250px" align="left"|Array
 
!width="250px" align="left"|Equivalent in SCM
 
|-
 
| <span style="color:blue">{{hint|$150(3@,6f)|Sanny Builder syntax}}</span>||{{hint|07|Data type}}&nbsp;&nbsp;&nbsp;{{hint|96 00|Array offset}}&nbsp;{{hint|03 00|Array index}}&nbsp;{{hint|06|Array size}}&nbsp;{{hint|01|Array properties}}
 
|-
 
| <span style="color:blue">{{hint|10@(9@,5s)|Sanny Builder syntax}}</span>||{{hint|0D|Data type}}&nbsp;&nbsp;&nbsp;{{hint|0A 00|Array offset}}&nbsp;{{hint|09 00|Array index}}&nbsp;{{hint|05|Array size}}&nbsp;{{hint|02|Array properties}}
 
|}
 
  
 
== Notes ==
 
== Notes ==
{{note|vcstr}} In [[GTA 3]], [[Vice City]] and [[Liberty City Stories]], short strings (8 characters) have no type code. If the first byte of an argument does not fit data type range (<code>0x0</code> - <code>0x6</code> for GTA 3 and VC), it's recognized as the beginning of a string and the remaining 7 bytes of the string are read.
+
{{note|vcstr}} In [[GTA 3]], [[Vice City]] and [[Liberty City Stories]], short strings (8 bytes) have no type code. If the first byte of an argument does not fit data type range (<code>0x0</code> - <code>0x6</code> for GTA 3 and VC), it's recognized as the beginning of a string and the remaining 8 bytes of the string are read.
 
 
{{note|partype0}} Some instructions have a variable number of parameters. One such instruction is [[004F]] that starts a new [[script]]. To allow extra script setup, the instruction can take a variable number of arguments. The game uses the special data type to end such argument lists.
 
  
For non-variadic instructions, the maximum number of parameters is 16 for GTA 3 and VC and 32 for SA, LCS and VCS. Variadic instructions can be passed a maximum of 18 arguments in GTA 3 and VC; 34 for SA; and 106 for LCS and VCS, though these values are unconfirmed.
+
{{note|partype0}} Some instructions have a variable number of parameters. One such instruction is [[004F]] that starts a new [[script]] and takes a variable number of arguments to allow extra script setup. The game uses the special data type to end such argument lists. The number of input/output parameters an instruction can collect/store at a time (separately) is 16 for GTA 3 and VC and 32 for SA, LCS and VCS. Variadic instructions allows for passing additional arguments as much as the amount of local variables minus timers which is 16 for GTA 3 and VC, 32 for SA and 96 for LCS and VCS.
  
 
{{note|05B6}} In {{Icon|SA}}, [[05B6]] is a special instruction that defines a table. Immediately after the opcode a 128 byte stream of data follows, without a type code.
 
{{note|05B6}} In {{Icon|SA}}, [[05B6]] is a special instruction that defines a table. Immediately after the opcode a 128 byte stream of data follows, without a type code.

Latest revision as of 00:47, 14 February 2022

This article deals with the technical information on the SCM instruction format. For a list of opcodes along with descriptions, see list of opcodes.

An SCM instruction is a single operation in an SCM file. They are executed when the script is run, and are used to change what happens ingame.

Instruction format

Each instruction is comprised of an opcode and arguments.

  • The "opcode" (short for "operation code") is a number that tells the game which operation to perform. For example, the opcode 0001 tells the game to wait for a certain amount of time, 0003 shakes the game camera and 0053 creates a player. The opcode is a signed 16-bit integer.
  • "Arguments" are values sent with the instruction to change what it does. For example, you can change the amount of time to wait when using opcode 0001 by sending a different argument.

Before compilation, the instructions are written as text. For example, a wait instruction could look like this:

wait 0

where wait represents the opcode 0001 and the number 0 is an argument passed with the instruction. Different compilers may use different words to represent each opcode. When the code is compiled, the instruction is converted to raw bytes:

01 00 04 00
  • The first two bytes (01 00 hex) are the opcode bytes in little-endian order.
  • The third byte (04 hex) is the code for the data type.[*] 0x4 is the code for a signed byte.
  • The final byte (00 hex) is the argument value. This is often more than one byte: the size is determined by the data type.

While the opcode bytes are always present, there may not always be arguments passed, so there may be no argument bytes.

No GTA game uses all the available opcodes (32,767 or 0x7FFF). There are mods that add more instructions to the game, most notably the CLEO Library.

Although opcodes are typically considered as being two bytes long and thus 16 bits, actual opcodes only ever use 15 of those bits. This is because the most significant bit (0x8000) is reserved for use in compiled code as a way of telling the runtime to invert the return value of an operation. For example, IS_CHAR_DEAD has opcode 0x118 (0b100011000) and is used to find out if a given actor is dead. If a script wants to find if a character is not dead, the written opcode would be 0x8118 (0b1000000100011000), as the 0x8000 bit is set to 1 to invert the result. The inversion bit can be masked off by ANDing the written opcode with 0x7fff (op & 0x7fff).

Arguments

Each instruction takes a certain number of arguments. If a script passes an incorrect number of arguments, the game will crash.

An argument could be one of the following types:

Concrete data types

Each of the types listed above can be represented in a number of ways in compiled code for various reasons:

  • Integer values can be signed or unsigned, and there are also different sizes of integer that the game can use.
  • There are multiple types of string that allow different numbers of characters.
  • Variables use different type codes based on the type of value that they are referencing.

The concrete type of an argument is determined by a single byte before the value bytes[*]. This byte tells the game what value is coming next so that it knows how many bytes to read, and how to treat the value once read.

III/VC/SA

Type code
(hex)
Value length
(bytes)
Support Description 
Typified
00 0 GTA III Vice City San Andreas End of argument list (EOAL, 004F or 0913 and similar)[*]
01 4 GTA III Vice City San Andreas Immediate 32-bit signed int
value = ReadInt32(Bytecode, PC)
PC += 4
02 2 GTA III Vice City San Andreas Global integer/floating-point variable (offset)
globalVar = ReadUInt16(Bytecode, PC)
PC += 2
03 2 GTA III Vice City San Andreas Local integer/floating-point variable (index)
localVar = ReadUInt16(Bytecode, PC)
PC += 2
04 1 GTA III Vice City San Andreas Immediate 8-bit signed int
value = SignExtend32(ReadInt8(Bytecode, PC))
PC += 1
05 2 GTA III Vice City San Andreas Immediate 16-bit signed int
value = SignExtend32(ReadInt16(Bytecode, PC))
PC += 2
06 2 GTA III Immediate 16-bit fixed-point (see remark)
value = ToFloat32(ReadUInt16(Bytecode, PC)) / 16.0
PC += 2
06 4 Vice City San Andreas Immediate 32-bit floating-point
value = ReadFloat32(Bytecode, PC)
PC += 4
07 6 San Andreas Global integer/floating-point array (offset)
globalVar = ReadUInt16(Bytecode, PC)
arrayIndexVar = ReadUInt16(Bytecode, PC+2)
//arraySize = ReadUInt8(Bytecode, PC+4)
//elementType = ReadUInt8(Bytecode, PC+5) & 0x7F
isGlobalIndex = ReadUInt8(Bytecode, PC+5) >> 7
PC += 6
08 6 San Andreas Local integer/floating-point array (index)
localVar = ReadUInt16(Bytecode, PC)
arrayIndexVar = ReadUInt16(Bytecode, PC+2)
//arraySize = ReadUInt8(Bytecode, PC+4)
//elementType = ReadUInt8(Bytecode, PC+5) & 0x7F
isGlobalIndex = ReadUInt8(Bytecode, PC+5) >> 7
PC += 6
Typified (strings)
09 8 San Andreas Immediate 8-byte string
textLabel = ReadString(Bytecode, PC, 8)
PC += 8
0A 2 San Andreas Global 8-byte string variable (see 02)
0B 2 San Andreas Local 8-byte string variable (see 03)
0C 6 San Andreas Global 8-byte string array (see 07)
0D 6 San Andreas Local 8-byte string array (see 08)
0E 1+n San Andreas Immediate variable-length string (non null-terminated)
length = ReadInt8(Bytecode, PC)
textLabel = ReadString(Bytecode, PC+1, length)
          + StrPad("\0", 40-length)
PC += 1+length
0F 16 San Andreas Immediate 16-byte string
textLabel = ReadString(Bytecode, PC, 16)
PC += 16
10 2 San Andreas Global 16-byte string variable (see 02)
11 2 San Andreas Local 16-byte string variable (see 03)
12 6 San Andreas Global 16-byte string array (see 07)
13 6 San Andreas Local 16-byte string array (see 08)
Untypified
N/A 8 GTA III Vice City Immediate 8-byte string[*]
textLabel = ReadString(Bytecode, PC, 8)
PC += 8
N/A 128 San Andreas Immediate 128-byte string
string = ReadString(Bytecode, PC, 128)
PC += 128

LCS/VCS

Type codes for Liberty City Stories and Vice City Stories are very different from other games:

  • In some instances, the type code itself denotes the argument value. For example:
    • 0x1 represents the integer value 0
    • 0x2 represents 0.0
  • The type code can sometimes denote a variable.
  • Floating point values are packed (8, 16 or 24 bits as opposed to the more common 32 bits).
Type code
(hex)
Value length
(bytes)
Support Description 
Typified
00 0 Liberty City Stories Vice City Stories End of argument list (EOAL)
01 0 Liberty City Stories Vice City Stories Immediate 8-bit signed integer constant 0
value = 0
02 0 Liberty City Stories Vice City Stories Immediate 8-bit floating-point constant 0.0
value = 0.0
03 1 Liberty City Stories Vice City Stories Immediate 8-bit packed floating-point
value = AsFloat32(ReadUInt8(Bytecode, PC) << 24)
PC += 1
04 2 Liberty City Stories Vice City Stories Immediate 16-bit packed floating-point
value = AsFloat32((ReadUInt8(Bytecode, PC) << 16)
                | (ReadUInt8(Bytecode, PC+1) << 24))
PC += 2
05 3 Liberty City Stories Vice City Stories Immediate 24-bit packed floating-point
value = AsFloat32((ReadUInt8(Bytecode, PC) << 8)
                | (ReadUInt8(Bytecode, PC+1) << 16)
                | (ReadUInt8(Bytecode, PC+2) << 24))
PC += 3
06 4 Liberty City Stories Vice City Stories Immediate 32-bit signed integer
value = ReadInt32(Bytecode, PC)
PC += 4
07 1 Liberty City Stories Vice City Stories Immediate 8-bit signed integer
value = SignExtend32(ReadInt8(Bytecode, PC))
PC += 1
08 2 Liberty City Stories Vice City Stories Immediate 16-bit signed integer
value = SignExtend32(ReadInt16(Bytecode, PC))
PC += 2
09 4 Liberty City Stories Vice City Stories Immediate 32-bit floating-point
value = ReadFloat32(Bytecode, PC)
PC += 4
0A n+NUL Vice City Stories Immediate null-terminated string[*]
textLabel = ReadString(Bytecode, PC)
PC += StrLen(textLabel)+1
Typified (script variables)
0A..0B 1 Liberty City Stories Local timers (TIMERA, TIMERB)
localVar = ReadUInt8(Bytecode, PC) + 0x5E
PC += 1
0B..0C 1 Vice City Stories Local timers (TIMERA, TIMERB)
localVar = ReadUInt8(Bytecode, PC) + 0x5D
PC += 1
0C..6B 1 Liberty City Stories Local integer/floating-point variable
localVar = ReadUInt8(Bytecode, PC) - 0x0C
PC += 1
0D..6C 1 Vice City Stories Local integer/floating-point variable
localVar = ReadUInt8(Bytecode, PC) - 0x0D
PC += 1
6C..CB 3 Liberty City Stories Local integer/floating-point array
localVar = ReadUInt8(Bytecode, PC) - 0x6C
arrayIndexVar = ReadUInt8(Bytecode, PC+1)
arraySize = ReadUInt8(Bytecode, PC+2)
PC += 3
6D..CC 3 Vice City Stories Local integer/floating-point array
localVar = ReadUInt8(Bytecode, PC) - 0x6D
arrayIndexVar = ReadUInt8(Bytecode, PC+1)
arraySize = ReadUInt8(Bytecode, PC+2)
PC += 3
CC..E5 2 Liberty City Stories Global integer/floating-point variable[*]
globalVar = ByteSwap16(ReadUInt16(Bytecode, PC) - 0xCC)
PC += 2
CD..E5 2 Vice City Stories Global integer/floating-point variable[*]
globalVar = ByteSwap16(ReadUInt16(Bytecode, PC) - 0xCD)
PC += 2
E6..FF 4 Liberty City Stories Vice City Stories Global integer/floating-point array
globalVar = ByteSwap16(ReadUInt16(Bytecode, PC) - 0xE6)
arrayIndexVar = ReadUInt8(Bytecode, PC+2)
arraySize = ReadUInt8(Bytecode, PC+3)
PC += 4
Untypified
N/A 8 Liberty City Stories Immediate 8-byte string
textLabel = ReadString(Bytecode, PC, 8)
PC += 8

^ This type was introduced in VCS due to the presence of string variables.

^ Given the data type range limit the largest global variable in LCS is 6655, in VCS is 6399.

Integer numbers

An integer is a number without a decimal or fractional component.

Size
(bytes)
Range
Signed Name Unsigned Name
1 -128 to 127 INT8, CHAR 0 to 255 UINT8, BYTE
2 -32,768 to 32,767 INT16, SHORT 0 to 65,535 UINT16, WORD, USHORT
4 -2,147,483,648 to 2,147,483,647 INT32, LONG 0 to 4,294,967,295 UINT32, DWORD, ULONG

Floating-point numbers

A floating point number is a number with a decimal component.

Size
(bytes)
Range Name
4 ±1.1754944×10-38 to ±3.4028234×1038 SINGLE, FLOAT

Strings

A string is a piece of text. Strings can include letters, numbers and symbols.

There are two kinds of string:

  • Fixed-length. This is the most common type of string and has been used since GTA 3. The string length is fixed. When compiled these strings occupy a certain number of bytes (8 or 16) even if the text is actually shorter (any unused bytes are filled with null values).
  • Variable-length (SA only). Variable-length strings are encoded as a single byte specifying the length followed by the string character bytes. These strings are not null-terminated. The maximum length depends on the instruction[*]. The longest in the original game is 40 characters.
String value Compiled bytes
"MAIN" 09   4D 41 49 4E 00 00 00 00
"MODDING" 09   4D 4F 44 44 49 4E 47 00
"SAVE_OUR_SOULS!" 0F   53 41 56 45 5F 4F 55 52 5F 53 4F 55 4C 53 21 00
"Variable length string" 0E   16   56 61 72 69 61 62 6C 65 20 6C 65 6E 67 74 68 20 73 74 72 69 6E 67

Arrays

In GTA SA, an array is a static reference to a group of successive variables. There is no actual representation of an array value as a concrete type, they do have type codes. When an "array" is passed as an argument to an instruction, what is actually passed is a specific variable in that array. For this reason, array elements are passed as variables of the type in the array – that is to say, a value from an array of global integer variables would be passed as a global integer variable. The game simply performs the extra step of retrieving the variable from the array before using it in the instruction.

This section describes the format of array accesses in GTA SA. Vice City also has arrays, but in a different format.

// Example; not real code.
// Applies only to GTA: SA.
struct ArrayAccess {
    enum ElementType : uint8_t {
        Int,
        Float,
        String8,
        String16
    };
    
    // Offset of first variable in the array.
    uint16_t startOffset;
    
    // Index being accessed ("array[index]").
    // This can be a local variable ("array[someLocalVar]") or a global variable ("array[someGlobalVar]").
    uint16_t index;
    
    // Array length.
    int8_t length;
    
    // Array element type. 7 bits.
    ElementType type : 7;
    
    // Determines whether the index is a global variable (true) or a local variable (false).
    // Only 1 bit.
    bool globalIndex : 1;
};

The array offset is a variable which should have a value more than or equal to 0 and smaller than the array size. Global and local variables can be used as index variables – the purpose of the globalIndex field is to tell the game which has been used. The first element in the array is at index 0, and the last is at length - 1.

Notes

^ In GTA 3, Vice City and Liberty City Stories, short strings (8 bytes) have no type code. If the first byte of an argument does not fit data type range (0x0 - 0x6 for GTA 3 and VC), it's recognized as the beginning of a string and the remaining 8 bytes of the string are read.

^ Some instructions have a variable number of parameters. One such instruction is 004F that starts a new script and takes a variable number of arguments to allow extra script setup. The game uses the special data type to end such argument lists. The number of input/output parameters an instruction can collect/store at a time (separately) is 16 for GTA 3 and VC and 32 for SA, LCS and VCS. Variadic instructions allows for passing additional arguments as much as the amount of local variables minus timers which is 16 for GTA 3 and VC, 32 for SA and 96 for LCS and VCS.

^ In San Andreas, 05B6 is a special instruction that defines a table. Immediately after the opcode a 128 byte stream of data follows, without a type code.

^ Post.png GTAForums: Post by Seemann describing limits for the long strings in SA

See also