BFEVFL

bfevfl is a binary file format for event flows.

Structures

bfevfl is a little endian format, so values are stored in little endian even on Wii U.

bfevfl uses pointers very heavily to refer to strings, to other sections, etc. All pointers are always 64 bit long -- since the same format is used on the Switch which is a 64 bit platform. They must be present in the #Relocation table if the file is to be loaded correctly by the official bfevfl code.

As a direct consequence, most sections don't have any fixed order. Therefore, this article will only document the data structures and mention the order Nintendo places sections in. For more details, it is recommended to look at the evfl library directly.

Another consequence is that sections must be aligned to 8-byte boundaries in most cases to avoid unaligned memory accesses (this is not as important for strings).

Header

Offset	Type	Description
0x0	char[8]	Magic ("BFEVFL\x00\x00")
0x8	u16	Version (0x0300)
0xa	u8	Unknown (must be zero)
0xb	u8	Unknown
0xc	u16	Byte order mark
0xe	u8	Alignment (to get the actual value: 1 << raw_value)
0xf	u8	Unknown
0x10	u32	File name offset
0x14	u16	Is relocated flag (set in memory)
0x16	u16	First block offset
0x18	u32	Relocation table offset
0x1c	u32	File size
0x20	u16	Number of flowcharts
0x22	u16	Number of timelines
0x24	u32	Padding
0x28	Flowchart*	Flowchart (nullptr if no flowchart)
0x30	Dictionary*	Flowchart name dictionary
0x38	Timeline*	Timeline (nullptr if no timeline)
0x40	Dictionary*	Timeline name dictionary

Relocation table

Offset	Type	Description
0x0	char[4]	Magic ("RELT")
0x4	u32	Offset to relocation table start
0x8	u32	Number of sections (almost always 1)
0xc	u32	Padding
0x10	Section[num_sections]	Sections

Relocation table section

Offset	Type	Description
0x0	void*	Alternative base offset (unused by Nintendo)
0x8	u32	Used to calculate the base pointer if an alternative base offset is used
0xc	u32	Data end offset (before alignment)
0x10	u32	Number of entries to skip
0x14	u32	Number of entries (includes skipped entries)
0x18	Entry[num_entries]	Entries

Relocation table entry

Offset	Type	Description
0x0	u32	Offset to pointers to relocate
0x4	u32	Bit field that determines which pointers need to be relocated (up to 32 contiguous pointers starting from the listed offset)

String pool

The string pool starts with the STR magic and contains 2-byte aligned strings. The magic is not checked at all since strings are directly referred to using pointers.

All strings in the pool are Pascal string, i.e. length-prefixed strings. The length is an unsigned 16 bit integer. Strings are stored in reverse order of their binary representation.

Dictionary

A dictionary is a data structure that is used to quickly look up the index of an element based on its name. Thus, they are always used in conjunction with an array of elements. However, the way the dictionary and the array are associated depends on the structure.

BFEVFL dictionaries are essentially binary radix trees (also called PATRICIA trees or tries). The structure contains a binary search tree and bit-by-bit comparisons of strings are done to navigate through it. It is extremely similar to the Wii U bfres "index group" structure, but with significant changes to the algorithm. The Switch bfres format shares the same algorithm.

Offset	Type	Description
0x0	char[4]	Magic ("DIC ")
0x4	u32	Number of entries (ignoring root entry)
0x8	Entry	Root entry
0x18	Entry[num_entries]	Entries

Dictionary entry

Offset	Type	Description
0x0	u32	Compact representation of bit index
0x4	u16	Next index if bit is 0
0x6	u16	Next index if bit is 1
0x8	PascalString*	Name

The compact representation of the bit index has two parts:

• Bits 3-7: index of the byte that should be checked
• Bits 0-2: index of the bit in that byte

A bit index can be translated to its compact representation using:

def get_compact_representation(bit_idx: int) -> int:
    byte_idx = bit_idx // 8
    return (byte_idx << 3) | (bit_idx - 8*byte_idx)

Section order

File

• Header (0x48 bytes)
• Flowchart* array if it exists
• Flowchart dictionary (always)
• Timeline* array if it exists
• Timeline dictionary (always)
• Timeline
• Flowchart
• String pool (STR )
• Relocation table (RELT)

Flowchart

• Flowchart header
• Actors

• Argument name is put in the string pool.

• Events
• Entry point dictionary
• Entry points
• Event param containers, fork structs, etc. (in order)
• Actor param containers, string pointer arrays (in order)
• Entry point extra data

• Sub flow event index arrays are written here
• ptr_x10 data may be written here? (ptr_x10 has always been a nullptr in files that have been checked by leoetlino.)
• The size for each entry point is sizeof(event_idx_array) rounded up to the nearest multiple of 8 + 0x18 bytes.

Container

• Container header (variable size)
• Container dictionary
• Container items (+ values)

Tools

• evfl: Python library for parsing and writing event flows
• EventEditor: graphical editor for event flows