FelineSystem2

An open source remake of the CatSystem2 visual novel engine.

Demo

A makeshift demo of the current version can be found here.

Controls

Click/Scroll - Advance text

Ctrl/Enter - Advance text, hold to skip

SPACE - Hide message window

f - Toggle fullscreen

1-9 - Select choice

Shift + Alt + 1-9 - Quick save to slot 1-9

Shift + 1-9 - Quick load from slot 1-9

Features

• Multi-platform (WASM, Windows SDL2)
• Raw KIF archive decryption
• HG-3 image decoding and caching
• Custom-built CatScene recursive-descent parser

KIF Database Structure

FelineSystem2 implements a custom database of the game's KIF archives and assets, stored as a binary file.

Archive Table

Data Type	Value	Description
char[len]	ArchiveName	NULL-terminated filename of the KIF archive
uint32	EntryCount	Number of entries in archive
unsigned char	IsEncrypted	0x01 if archive is encrypted, 0x00 otherwise
byte[4]	FileKey	Blowfish key for decrypting entries (Only exists if IsEncrypted is 0x01)
0x00	TableEnd	Signifies end of table

Archive Item Entry

Data Type	Value	Description
char[len]	FileName	NULL-terminated deobfuscated filename
uint32	Offset	The offset to the entry's data
uint32	Length	The length of the entry's data

Notes

Parser

• If statements must contain a whitespace after the closing parenthesis of the condition
  • if (#300==0) #(950+#300)=512
• Operators follow C-Style left-to-right precedence and associativity
• Integers and strings are the only data types that exist
  • #300=0
  • str 50 bg02
• Variable names can only be integers
• Variable names can be dynamically evaluated
  • #(950+#300)=512

Script

• blend argument specifies the alpha value that the image will be displayed at
  • cg 0 blend 255 will display a completely opaque CG while cg 0 blend 0 will display a completely transparent CG
• rdraw command after an image specifies the duration to fade to the target opacity
  • rdraw 30 will take 30 frames to fade the image from alpha 0 to the target alpha (e.g. 255 by default)
  • Units are likely in frames at 60fps (0.0167s/frame) regardless of the game's refresh rate setting
  • An rdraw command will apply to all images within a script block (from a user input to the next wait command)
• wait command without arguments will block until any time-based command completes
  • wait after a rdraw 30 command will wait for the 30 frames taken to completely fade in the images before proceeding to the next command
• wait with arguments behaves differently from standalone wait
  • wait 60 will block for 60 frames before proceeding to the next command
  • wait 60 will not be aware of any time-based commands like rdraw and will not block until rdraw completes
  • wait is sometimes used along with wait 60 consecutively
• cg 0 attr 1 (70+0) (80+0)
• cg 0 attr 2 (75+0) (85+0)
  • Assigns the BaseX, BaseY values of the specified image cg 0 to the variables #(75+0) and #(85+0) respectively

Special Thanks

• Trigger for creating such an amazingly comprehensive knowledgebase of the CS2 engine
• asmodean for being a pioneer in reversing the CS2 engine
• Dodder for Hacking the Grisaia for localization
• koestl for his impeccable translations and contributions to localization