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pft.md

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A file with the .pft extension represents a 1-bit bitmap font that has been compiled by pdc. This format uses little endian byte order.

Header

Offset Type Detail
0 char[12] Ident Playdate FNT
12 uint32 Flags

Flags

Bitmask Detail
flags & 0x80000000 If > 0, the data in this file is compressed
flags & 0x00000001 If > 0, the font contains characters above U+1FFFF

Font Header

If the compression flag is set, there's an extra font header after the file header. Everything after this is zlib-compressed.

Offset Type Detail
0 uint32 Size of font data section when decompressed
4 uint32 Maximum glyph width (in pixels)
8 uint32 Maximum glyph height (in pixels)

Page List

Page List Header

Offset Type Detail
0 uint8 Glyph width (in pixels)
1 uint8 Glyph height (in pixels)
2 uint16 Tracking (in pixels)
4 64 bytes Page Usage Flags

Font glyphs are grouped into pages based on their unicode codepoints. Each page covers a span of 256 glyphs. Pages are only stored if they have glyphs present in the font.

The page index for a given glyph codepoint will be codepoint >> 8.

Following this header is a list of uint32 offsets for all of the pages present in the file, with the pages following immediately after.

Page Usage Flags

This contains bitflags for each page, starting at the lowest significant bit in the first byte. If a page's corresponding usage flag is 1, then it is present in the file.

Page

Page Header

Offset Type Detail
0 uint24 Reserved? Seen as 0
3 uint8 Number of glyphs
4 32 bytes Glyph Usage Flags

After the page header is a series of Glyphs for the page.

Glyph Usage Flags

This contains bitflags for each glyph, starting at the lowest significant bit in the first byte. If a glyph's corresponding usage flag is 1, then it is present in the page.

Glyph

Each glyph is comprised of:

  • a header
  • a short kerning table
  • (if necessary) padding bytes to align to the next multiple of 4
  • a long kerning table
  • pixel data

Glyph Header

Offset Type Detail
0 uint8 Glyph advance / width (in pixels)
1 uint8 Number of Short Kerning Table Entries
2 uint16 Number of Long Kerning Table Entries

Short Kerning Table Entries

I think this is for codepoints within the same page?

Offset Type Detail
0 uint8 Other glyph codepoint
1 int8 Kerning (in pixels)

Long Kerning Table Entries

This supports any unicode codepoint within the whole font

Offset Type Detail
0 uint24 Other glyph codepoint
3 int8 Kerning (in pixels)

Glyph pixels

Stored as an Image Cell.