CST Scene

File Structure fully deciphered!

Decompiling not guaranteed to be fully deciphered, need to play around with custom line type values.

The structure and basic language syntax for Cat Scenes are slightly over 20 years old now, as they existed in the original CatSystem (1) engine in the late 1990's.

File Structure

Data Type	Value	Description
char[8]	"CatScene"	File Signature
uint32	CompressedSize	Compressed size of ScriptData (uncompressed when 0)
uint32	DecompressedSize	Decompressed size of ScriptData
byte[CompressedSize]	ScriptData	Zlib-compressed scene script contents

Note: When CompressedSize is 0, ScriptData is stored in its full uncompressed format. Read byte[DecompressedSize] instead. This occurs when compiling in mc.exe with the /x (-x) flag.

ScriptData Structure

Header

Data Type	Value	Description
uint32	ScriptLength	Size of ScriptData excluding sizeof(Header)
uint32	InputCount	Number of Input Offsets
uint32	OffsetTable	Offset to String Offset Table
uint32	StringTable	Offset to String Table

EntryCount = (StringTable - OffsetTable) / 4

Input Offset Table

These values can be calculated programmatically and are not necessary to read when parsing the file. They mark the offsets and indexes of the script line after every Input Flag line and most likely aid the game engine in skipping.

N = InputCount

Data Type	Value	Description
uint32	OffsetNext	Offset from Index to line after next input
uint32	Index	Index of line after input

StringOffset Table

Position = sizeof(Header) + OffsetTable
N = EntryCount

Data Type	Value	Description
uint32	Offset	Offset of to String n

String Table

The string table for script lines. Each line has a type that determines what it does, and content that is either used to parse a command or display a message or name.

Position = sizeof(Header) + StringTable + StringOffsets[n]
N = EntryCount

Data Type	Value	Description
byte	0x01	Byte before Type, hardcoded as 0x01
byte	Type	Action performed by the line
string	Content	Content of the line

The 0x01 prefix byte could be some sort of count (like number of strings), or a reserved format planned for use in the future. Whatever the case, the engine only knows how to read and write 0x01.

LineTypes

Line type names are accurate to internal usage, as they're always printed to the debug log in-game.

Name	Value	Description
Input	0x02	Wait for input after message
Page	0x03	Novel page break and wait for input after message
Message	0x20	Display a message
Name	0x21	Set speaker of the message
Command	0x30	Perform any other command
ScriptName	0xF0	Sets the name of the source script file
LineNumber	0xF1	Marks the current line number in the source script file (as a string)

Some things to note:

• ScriptName and LineNumber line types are debug information only. These are inserted by mc.exe when compiling with the /l (-l) flag. These can safely be skipped, however they do allow for some extended information when decompiling.
• Input line types are the only one to use the flag 0x02 in their value, though it's also true that they have 0x0_ for their most significant digit.
• All message-related line types have 0x2_ for their most significant digit.

See Also

• CSTL Scene Languages
• Tool: mc.exe