Background/Arena File Format (.BK)

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The BK file format is similar in many ways to the AF file format, however, there are some signifigant differences.

Header

Unknown 1 DWORD 0 for INTRO, 2 for ending cutscenes,4 for main menu/newsroom/VS/Mechlab/melee, 6 for credits,

8 for Arena0, 16 for Arena1, 32 for Arena2, 64 for Arena3 and 128 for Arena4

Unknown 1 BYTE ? 1, 2 or variable
Width 1 WORD Background width (always 320?)
Height 1 WORD Background height (always 200?)

Animations

Each animation is preceded by the offset of the next animation stored as a DWORD, along with an animation number. Reading the animation and advancing the file pointer should result in the file pointer being the same as the next animation offset. An animation number >= 50 marks the end of the animations section. When this occurs, the next animation offset is set to the offset of the current animation.

Next animation 1 DWORD Position of next animation relative to start of file, in bytes
Animation number 1 BYTE Unique identifier for animation

Animation Header

Unknown 1 BYTE Nul padding?
Unknown 1 BYTE
Unknown 1 BYTE
Unknown 1 BYTE
Unknown 1 WORD
Unknown 1 BYTE
Something size 1 WORD
Something N BYTES Size is determined by the previous value

There then follows an animation structure (see .AF file format).

Footer

After the animations there is a footer structure:

Background image W*H BYTES W and H are the width and height in the file header
Num palettes 1 BYTE Specifies the number of palettes which follow

Palettes

Palette data 256*3 BYTES A palette
Unknown 1024 BYTES
Unknown 3840 BYTES

Rest of footer

Unknown 30 BYTES