BFEVFL

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bfevfl is a binary file format for event flows. In Breath of the Wild and other Nintendo games such as Splatoon 2, binary event flows are parsed by Nintendo's EventFlow/evfl library.

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

Note: 0x0-0x20 are just a standard ore::BinaryFileHeader (which is identical to nn::util::BinaryFileHeader).

Relocation table

(The official name for this structure in the EventFlow library is ore::RelocationTable.)

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

Note: the number of sections is almost always 1 because a single section can already fit 2^32 - 1 entries. If you need more than 4 billion entries, you are probably doing something very wrong.

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 official name for this structure in the EventFlow library is ore::StringPool.)

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

Dictionary

(The official name for this structure in the EventFlow library is ore::ResDic.)

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 (bit index is 0xffffffff)
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)

Example: Hello corresponds to 100100001100101011011000110110001101111. Bits 0-3 are 1, bit 4 is 0, etc.

Container

(The official name for this structure in the EventFlow library is ore::ResMetadata.)

Containers are key-value mappings with keys being strings. A #Dictionary is used to store keys.

Offset Type Description
0x0 ContainerItem Root container structure (data type is Container)

ContainerItem

Offset Type Description
0x0 ContainerDataType (u8) Data type
0x1 u8 Padding
0x2 u16 Number of items
0x4 u32 Padding
0x8 Dictionary* Dictionary (only for the Container data type)
0x10 ContainerItemData Data

ContainerItemData

Data type Data Number of items
Argument String (not in string pool, follows item structure immediately) 1
Container ContainerItem*[n] n
Int Signed 32-bit integer 1
Bool 0x80000001 if true, 0x00000000 otherwise 1
Float binary32 floating point number 1
String String (not in string pool, follows item structure immediately) 1
Wide string ("wstring") (not implemented) ?
Int array Int[n] n
Bool array Bool[n] n
Float array Float[n] n
String array String[n] (aligned to 8-byte boundaries this time) n
Wstring array (not implemented) ?
Actor identifier Two strings: actor name + secondary name 2

ContainerDataType enum

The following enum definition is complete and all names are official[1].

Value Name
0 Argument
1 Container
2 Int
3 Bool
4 Float
5 String
6 Wide string ("wstring")
7 Int array
8 Bool array
9 Float array
10 String array
11 Wstring array
12 Actor identifier

Actor

(The official name for this structure in the EventFlow library is evfl::ResActor.)

Offset Type Description
0x0 PascalString* Name
0x8 PascalString* Secondary name
0x10 PascalString* Argument name
0x18 #evfl::ResAction* Pointer to array of actions (strings)
0x20 #evfl::ResQuery* Pointer to array of queries (strings)
0x28 Container* Parameters
0x30 u16 Number of actions
0x32 u16 Number of queries
0x34 u16 Entry point index for associated entry point (0xffff if none)
0x36 u8 Cut number? This is set to 1 for flowcharts. Timeline actors sometimes use a different value here. [check] In BotW, this value is passed as the @MA actor parameter[2].
0x37 u8 Padding

evfl::ResAction

Offset Type Description
0x0 PascalString* Name

evfl::ResQuery

Offset Type Description
0x0 PascalString* Name

Event

EventType enum

(The official name for this enum in the EventFlow library is evfl::ResEvent::EventType::Type.)

Value Name Description
0 Action Invokes an actor function ("action") with no return value.
1 Switch Invokes an actor function ("query") with an int return value and branches execution flow depending on it.
2 Fork Branches execution flow unconditionally.
3 Join Used to reunify execution flow after a fork finishes executing.
4 Sub flow Invokes an entry point in the same or in a different event flow. Similar to a function call.

Main event structure

(The official name for this structure in the EventFlow library is evfl::ResEvent.)

Offset Type Description
Action Switch Fork Join Sub flow
0x0 PascalString* Name
0x8 EventType (u8) Type
0x9 u8 Padding
0xa u16 Next event index Number of cases (>=0) Number of forks (>0) Next event index
0xc u16 Actor index Join event index (required) Unused
0xe u16 Actor action index Actor query index Unused
0x10 void* Container* (optional parameters) u16* (fork event indexes) Unused Container* (optional parameters)
0x18 void* Unused SwitchCases* (0x0: u32 value, 0x4: u16 event index, 0x6: u16 padding) Unused PascalString* (flowchart name)
0x20 void* Unused PascalString* (entry point name)

Entry point

(The official name for this structure in the EventFlow library is evfl::ResEntryPoint.)

Offset Type Description
0x0 u16* Sub flow event indices
0x8 Dictionary* VariableDef names (parsed by the evfl lib, but unused by BotW)
0x10 VariableDef* VariableDefs (parsed by the evfl lib, but unused by BotW)
0x18 u16 Number of sub flow event indices
0x1a u16 Number of variable definitions
0x1c u16 Main event index
0x1e u16 Padding

Flowchart

(The official name for this structure in the EventFlow library is evfl::ResFlowchart.)

Offset Type Description
0x0 char[4] Magic ("EVFL")
0x4 u32 String pool offset (relative to this structure)
0x8 u32 Padding
0xc u32 Padding
0x10 u16 Number of actors
0x12 u16 Total number of actions
0x14 u16 Total number of queries
0x16 u16 Number of events
0x18 u16 Number of entry points
0x1a u16 Padding
0x1c u16 Padding
0x1e u16 Padding
0x20 PascalString* Name
0x28 Actor* Actors
0x30 Event* Events
0x38 Dictionary* Entry point dictionary
0x40 EntryPoint* Entry points

Timeline

(The official name for this structure in the EventFlow library is evfl::ResTimeline.)

Offset Type Description
0x0 char[4] Magic ("TLIN")
0x4 u32 String pool offset (relative to this structure)
0x8 u32 Padding
0xc u32 Padding
0x10 float Duration
0x14 u16 Number of actors
0x16 u16 Total number of actions
0x18 u16 Number of clips
0x1a u16 Number of oneshots
0x1c u16 Number of subtimelines
0x1e u16 Number of cuts
0x20 PascalString* Name
0x28 Actor* Actors
0x30 #Clip* Clips
0x38 #Oneshot* Oneshots
0x40 #Trigger* Triggers (exactly 2 per clip)
0x48 #Subtimeline* Subtimelines
0x50 #Cut* Cuts
0x58 Container* Parameters

Clip

(The official name for this structure in the EventFlow library is evfl::ResClip.)

Offset Type Description
0x0 float Start time
0x4 float Duration
0x8 u16 Actor index
0xa u16 Actor action index
0xc u8 ? [check]
0xd u8[3] Padding
0x10 Container* Parameters

Oneshot

(The official name for this structure in the EventFlow library is evfl::ResOneshot.)

Offset Type Description
0x0 float Time
0x4 u16 Actor index
0x6 u16 Actor action index
0x8 void* Padding
0x10 Container* Parameters

Trigger

(The official name for this structure in the EventFlow library is evfl::ResTrigger.)

Offset Type Description
0x0 u16 Clip index
0x2 #TriggerType Trigger type
0x3 u8 Padding

TriggerType

Value Description
1 Enter - triggered when a clip starts
2 Leave - triggered when a clip ends

Cut

(The official name for this structure in the EventFlow library is evfl::ResCut.)

Offset Type Description
0x0 float Start time [check]
0x4 u32 ? [check]
0x8 PascalString* Name
0x10 Container* Parameters

Subtimeline

(The official name for this structure in the EventFlow library is evfl::ResSubtimeline.)

Offset Type Description
0x0 PascalString* Subtimeline name

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)

Timeline

  • Actor param containers, evfl::ResAction
  • Parameter container
  • Timeline header
  • Actors
  • Clips
  • Oneshots [check]
  • Subtimelines
  • Triggers
  • Cuts
  • Clip param containers
  • Oneshot param containers [check]
  • Cut param containers [check]

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)

Usage in Breath of the Wild

BFEVFL is used as the underlying format for event flows in the release versions. They are always stored under EventFlow and have "bfevfl" (for flowcharts) and "bfevtm" (for timelines) as their file extensions.

For development versions, it appears that a different, non-binary format was used ("evfl").

Tools

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

  1. 0x7101DA3EC8 in Switch 1.5.0
  2. Switch 1.5.0 0x7100DA8628