HarfBuzz + FreeType font backend. More...

#include "donner/svg/text/TextBackendFull.h"

Inheritance diagram for donner::svg::TextBackendFull:

Collaboration diagram for donner::svg::TextBackendFull:

Classes
struct	HbFontEntry
	Internal storage for a HarfBuzz font object backed by FreeType. The hb_font_t is created via hb_ft_font_create_referenced(), which holds a reference to the FT_Face. We also hold our own reference (from FT_New_Memory_Face). Destruction order: destroy hb_font first (decrefs FT_Face from 2->1), then FT_Done_Face (decrefs 1->0, frees). More...

Public Member Functions
	TextBackendFull (FontManager &fontManager, Registry &registry)
	TextBackendFull (const TextBackendFull &)=delete
TextBackendFull &	operator= (const TextBackendFull &)=delete
FontVMetrics	fontVMetrics (FontHandle font) const override
	Vertical metrics (ascent, descent, lineGap) in font design units.
float	scaleForPixelHeight (FontHandle font, float pixelHeight) const override
	Scale factor: font design units → pixels, normalized to ascent−descent height. This is stbtt_ScaleForPixelHeight semantics.
float	scaleForEmToPixels (FontHandle font, float pixelHeight) const override
	Scale factor: em units → pixels. Differs from scaleForPixelHeight when ascent−descent != unitsPerEm. This is the correct scale for CSS font-size.
std::optional< UnderlineMetrics >	underlineMetrics (FontHandle font) const override
	Underline position/thickness from the 'post' table, in font design units. Returns std::nullopt if the table is missing.
std::optional< UnderlineMetrics >	strikeoutMetrics (FontHandle font) const override
	Strikeout position/thickness from the OS/2 table, in font design units. Returns std::nullopt if the table is missing.
std::optional< SubSuperMetrics >	subSuperMetrics (FontHandle font) const override
	Sub/superscript Y offsets from the OS/2 table, in font design units. Returns std::nullopt if the table is missing.
Path	glyphOutline (FontHandle font, int glyphIndex, float scale) const override
	Extract a glyph outline as a Path. Coordinates are in font units scaled by `scale`, with Y flipped for SVG's y-down convention.
bool	isBitmapOnly (FontHandle font) const override
	Returns true if the font is bitmap-only (no vector outlines).
bool	isCursive (uint32_t codepoint) const override
	Returns true if letter-spacing should be suppressed for this codepoint (cursive/connected scripts like Arabic). Simple backends return false.
bool	hasSmallCapsFeature (FontHandle font) const override
	Returns true if the font has a native OpenType small-caps feature (smcp). If false, the engine synthesizes small-caps via uppercase + reduced size.
std::optional< BitmapGlyph >	bitmapGlyph (FontHandle font, int glyphIndex, float scale) const override
	Extract a bitmap glyph (CBDT/CBLC color emoji). Returns std::nullopt if the glyph is not a bitmap. Simple backends always return std::nullopt.
ShapedRun	shapeRun (FontHandle font, float fontSizePx, std::string_view spanText, size_t byteOffset, size_t byteLength, bool isVertical, FontVariant fontVariant, bool forceLogicalOrder) const override
	Shape a range of text, producing glyph IDs with advances and kerning.
double	crossSpanKern (FontHandle prevFont, float prevSizePx, FontHandle curFont, float curSizePx, uint32_t prevCodepoint, uint32_t curCodepoint, bool isVertical) const override
	Compute cross-span kerning between the last codepoint of the previous span and the first codepoint of the current span.

Detailed Description

HarfBuzz + FreeType font backend.

Provides full OpenType shaping (GSUB/GPOS), FreeType glyph outlines, cursive script detection, native small-caps queries, and bitmap glyph extraction (CBDT/CBLC).

Member Function Documentation

◆ bitmapGlyph()

std::optional< TextBackend::BitmapGlyph > donner::svg::TextBackendFull::bitmapGlyph	(	FontHandle	font,
		int	glyphIndex,
		float	scale ) const

overridevirtual

Extract a bitmap glyph (CBDT/CBLC color emoji). Returns std::nullopt if the glyph is not a bitmap. Simple backends always return std::nullopt.

Implements donner::svg::TextBackend.

◆ crossSpanKern()

double donner::svg::TextBackendFull::crossSpanKern	(	FontHandle	prevFont,
		float	prevSizePx,
		FontHandle	curFont,
		float	curSizePx,
		uint32_t	prevCodepoint,
		uint32_t	curCodepoint,
		bool	isVertical ) const

overridevirtual

Compute cross-span kerning between the last codepoint of the previous span and the first codepoint of the current span.

Returns: Kern adjustment in pixels (added to pen position).

Implements donner::svg::TextBackend.

◆ fontVMetrics()

FontVMetrics donner::svg::TextBackendFull::fontVMetrics ( FontHandle font ) const

overridevirtual

Vertical metrics (ascent, descent, lineGap) in font design units.

Implements donner::svg::TextBackend.

◆ glyphOutline()

Path donner::svg::TextBackendFull::glyphOutline	(	FontHandle	font,
		int	glyphIndex,
		float	scale ) const

overridevirtual

Extract a glyph outline as a Path. Coordinates are in font units scaled by scale, with Y flipped for SVG's y-down convention.

Implements donner::svg::TextBackend.

◆ hasSmallCapsFeature()

bool donner::svg::TextBackendFull::hasSmallCapsFeature ( FontHandle font ) const

overridevirtual

Returns true if the font has a native OpenType small-caps feature (smcp). If false, the engine synthesizes small-caps via uppercase + reduced size.

Implements donner::svg::TextBackend.

◆ isBitmapOnly()

bool donner::svg::TextBackendFull::isBitmapOnly ( FontHandle font ) const

overridevirtual

Returns true if the font is bitmap-only (no vector outlines).

Implements donner::svg::TextBackend.

◆ isCursive()

bool donner::svg::TextBackendFull::isCursive ( uint32_t codepoint ) const

overridevirtual

Returns true if letter-spacing should be suppressed for this codepoint (cursive/connected scripts like Arabic). Simple backends return false.

Implements donner::svg::TextBackend.

◆ scaleForEmToPixels()

float donner::svg::TextBackendFull::scaleForEmToPixels	(	FontHandle	font,
		float	pixelHeight ) const

overridevirtual

Scale factor: em units → pixels. Differs from scaleForPixelHeight when ascent−descent != unitsPerEm. This is the correct scale for CSS font-size.

Implements donner::svg::TextBackend.

◆ scaleForPixelHeight()

float donner::svg::TextBackendFull::scaleForPixelHeight	(	FontHandle	font,
		float	pixelHeight ) const

overridevirtual

Scale factor: font design units → pixels, normalized to ascent−descent height. This is stbtt_ScaleForPixelHeight semantics.

Implements donner::svg::TextBackend.

◆ shapeRun()

TextBackend::ShapedRun donner::svg::TextBackendFull::shapeRun	(	FontHandle	font,
		float	fontSizePx,
		std::string_view	spanText,
		size_t	byteOffset,
		size_t	byteLength,
		bool	isVertical,
		FontVariant	fontVariant,
		bool	forceLogicalOrder ) const

overridevirtual

Shape a range of text, producing glyph IDs with advances and kerning.

The full span text and a byte range within it are provided so context-aware backends (HarfBuzz) can use surrounding context for GSUB/GPOS.

Parameters

font	Font to shape with.
fontSizePx	Font size in pixels.
spanText	Full span text (UTF-8).
byteOffset	Start of the range to shape within `spanText`.
byteLength	Length of the range to shape.
isVertical	True for vertical writing mode.
fontVariant	Font variant (Normal or SmallCaps).
forceLogicalOrder	If true, return glyphs sorted by cluster (DOM order) rather than visual order. Used for per-character positioned RTL text.

Returns: Shaped glyphs with advances, kerning, and cluster mapping.

Implements donner::svg::TextBackend.

◆ strikeoutMetrics()

std::optional< UnderlineMetrics > donner::svg::TextBackendFull::strikeoutMetrics ( FontHandle font ) const

overridevirtual

Strikeout position/thickness from the OS/2 table, in font design units. Returns std::nullopt if the table is missing.

Implements donner::svg::TextBackend.

◆ subSuperMetrics()

std::optional< SubSuperMetrics > donner::svg::TextBackendFull::subSuperMetrics ( FontHandle font ) const

overridevirtual

Sub/superscript Y offsets from the OS/2 table, in font design units. Returns std::nullopt if the table is missing.

Implements donner::svg::TextBackend.

◆ underlineMetrics()

std::optional< UnderlineMetrics > donner::svg::TextBackendFull::underlineMetrics ( FontHandle font ) const

overridevirtual

Underline position/thickness from the 'post' table, in font design units. Returns std::nullopt if the table is missing.

Implements donner::svg::TextBackend.

The documentation for this class was generated from the following files:

donner/svg/text/TextBackendFull.h
donner/svg/text/TextBackendFull.cc

Classes

Public Member Functions

Detailed Description

Member Function Documentation

◆ bitmapGlyph()

◆ crossSpanKern()

◆ fontVMetrics()

◆ glyphOutline()

◆ hasSmallCapsFeature()

◆ isBitmapOnly()

◆ isCursive()

◆ scaleForEmToPixels()

◆ scaleForPixelHeight()

◆ shapeRun()

◆ strikeoutMetrics()

◆ subSuperMetrics()

◆ underlineMetrics()