Mojo struct 🡭

FontCache

@memory_only
struct FontCache

Construct one, then pass it by cache= into draw_text/measure_text/measure_text_block for every call reusing the same fonts. No cleanup, and no setup: the one font scan happens on the first lookup, and every later lookup skips it.

Implemented traits

AnyType, Deinitable, Movable

Methods

__init__

fn def __init__(out self)

Scans nothing. The installed fonts are read on the first lookup that misses the path dictionaries – see this module’s docstring for why once, and why then.

Args:

• self (Self)

Returns:

Self

has_scanned

fn def has_scanned(self) -> Bool

Whether the installed fonts have been scanned yet: False after construction, True from the first lookup that needed them.

Args:

• self (Self)

Returns:

Bool: True once the scan has happened.

glyph_mask_count

fn def glyph_mask_count(self) -> Int

How many rasterized glyph masks the cache holds.

Args:

• self (Self)

Returns:

Int: The number of distinct (face, size, codepoint, sub-pixel offset) masks cached so far, across both generations.

glyph_mask_bytes

fn def glyph_mask_bytes(self) -> Int

How much the rasterized-glyph store is holding.

Counts each entry’s mask, its key, and a fixed charge for the dictionary slot around them, across both generations. Stays under _GLYPH_MASK_BUDGET except while a single mask larger than a generation’s share is live, which is possible only for very large text and lasts one turnover.

Args:

• self (Self)

Returns:

Int: Bytes currently held.

glyph_mask_turnovers

fn def glyph_mask_turnovers(self) -> Int

How many times the store has released a generation.

Zero until a run of distinct glyphs reaches one of the two bounds. Useful for confirming that a workload actually exercises eviction rather than merely fitting.

Args:

• self (Self)

Returns:

Int: The number of turnovers so far.

clear_glyph_masks

fn def clear_glyph_masks(mut self)

Release every rasterized glyph mask, keeping the resolved font paths and faces. Later draws rasterize their masks again.

Args:

• self (Self)

resolve

fn def resolve(mut self, family: String, slant: FontSlant, weight: FontWeight) -> String

Cached resolve_font_file: the scanned font database is matched once per distinct (family, slant, weight), and every later call for that combination reads the path from the Dict.

Args:

• self (Self)
• family (String): Font family name or generic alias.
• slant (FontSlant): Requested upright/italic/oblique style.
• weight (FontWeight): Requested normal/bold weight.

Returns:

String: The matched font’s absolute file path.

Raises:

Error: no fonts are installed on this machine.

resolve_for_char

fn def resolve_for_char(mut self, family: String, slant: FontSlant, weight: FontWeight, codepoint: Int) -> String

Cached resolve_font_file_for_char, keyed additionally on codepoint, since a charset-constrained match can return a different font than the unconstrained one.

Args:

• self (Self)
• family (String): Font family name or generic alias.
• slant (FontSlant): Requested upright/italic/oblique style.
• weight (FontWeight): Requested normal/bold weight.
• codepoint (Int): Unicode codepoint the matched font should contain.

Returns:

String: The matched font’s absolute file path.

Raises:

Error: no fonts are installed on this machine.

resolve_face

fn def resolve_face(mut self, family: String, slant: FontSlant, weight: FontWeight, size: Float64) -> ArcPointer[TTFFace]

resolve plus _face_for_path in one call. draw_text calls it twice per invocation, so with a shared cache the second is a hit.

Args:

• self (Self)
• family (String): Font family name or generic alias.
• slant (FontSlant): Requested upright/italic/oblique style.
• weight (FontWeight): Requested normal/bold weight.
• size (Float64): Pixel size to rasterize glyphs at.

Returns:

ArcPointer[TTFFace]: The resolved, sized font face, shared across every caller requesting the same (path, size).

Raises:

Error: no fonts are installed on this machine, or the resolved file can’t be parsed.

resolve_face_for_char

fn def resolve_face_for_char(mut self, family: String, slant: FontSlant, weight: FontWeight, codepoint: Int, size: Float64) -> ArcPointer[TTFFace]

resolve_face’s fallback-glyph counterpart. resolve_for_char deduplicates the path lookup; this also stops each fallback glyph from re-parsing the file.

Args:

• self (Self)
• family (String): Font family name or generic alias.
• slant (FontSlant): Requested upright/italic/oblique style.
• weight (FontWeight): Requested normal/bold weight.
• codepoint (Int): Unicode codepoint the matched font should contain.
• size (Float64): Pixel size to rasterize glyphs at.

Returns:

ArcPointer[TTFFace]: The resolved, sized font face, shared across every caller requesting the same (path, size).

Raises:

Error: no fonts are installed on this machine, or the resolved file can’t be parsed.