formats

README

nbarena/formats

This repository contains reading/writing code for the goofy formats that NetBattle Arena uses (they're real goofy!).

metapng

metapng is a PNG image with arbitrary metadata, stored in the zTXt chunk with the private use "compression scheme" 0xFF, with the keywords MPNG:<field name>. The zTXt chunk is used over the tEXt and iTXt chunk as it allows arbitrary binary data: tEXt expects Latin-1 and iTXt expects UTF-8: technically, the zTXt chunk expects the decompression output to be Latin-1, but we're able to fudge this by using a compression scheme constant that's not recognized by any program today.

oggloop

oggloop is a looping Ogg file, a la RPG Maker. The loop information is contained in the comment section under two tags labeled LOOPSTART and LOOPLENGTH. The value is an integer denoting the start of the loop and the length of the loop in number of samples.

pngatlas

pngatlas is a metapng file that contains region information in the atlas metapng field. The value of the field is compressed with zlib, and of the format x:int6be y:int64be w:int64be h:int64be. We use big endian here because the rest of the PNG format uses big endian, and it feels wrong to switch to little endian for this field.

pngsheet

pngsheet is a PNG file that contains a sprite sheet with animations. It additionally contains two metadata chunks, a supplementary palette in sPLT and an animation control section in zTXt with the keyword fsctrl and "compression scheme" 0xFF.

For BN6 rips, the sPLT section is expected to contain groups of 16 colors.

The fsctrl section is structured as follows:

left:       int16
top:        int16
right:      int16
bottom:     int16
originX:    int16
originY:    int16
delay:      uint8
action:     0x00 "next" | 0x01 "loop" | 0x03 "stop"

Each animation is delimited by a non-"next" action.