kitepdf-core/io.github.yuroyami.kitepdf.core.font/CffSubsetter

CffSubsetter

Subsets a CFF font program (the outlines inside an OpenType .otf) down to the glyphs a document uses, and re-emits it as a CID-keyed CFF.

The output is always CID-keyed with a charset that maps each new glyph id to its original glyph id (used as the CID). Under a PDF Type0 / CIDFontType0 / Identity-H font that means the content stream can keep emitting the original glyph id as the 2-byte code (identical to the TrueType path) and the reader resolves code → CID(=original gid) → new gid via this charset. So /W and /ToUnicode stay keyed by the original gid too.

Only the CharStrings INDEX is subset; all global and local subroutines are kept verbatim (their biased references stay valid), as do all FontDicts. For a CJK CFF the charstrings dominate, so this is the bulk of the size win without the complexity (and risk) of renumbering subrs. The deprecated seac-via- endchar accent composition is not followed, so a glyph built that way would lose its components. CID-keyed fonts don't use it.

Types

Subset

class Subset(val cff: ByteArray, val oldToNew: Map<Int, Int>)

Functions

subset

fun subset(cff: CffFont, usedGids: Set<Int>, unitsPerEm: Int = 1000): CffSubsetter.Subset

Subset cff to usedGids plus .notdef. unitsPerEm is the number of font units in an em, such as the head value of an OpenType font. A bare CFF program has 1000 by default (Adobe Technical Note 5176, Table 9), so the subset records any other value in its FontMatrix.