stb_truetype-based font backend. More...

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

Inheritance diagram for donner::svg::TextBackendSimple:

Public Member Functions
	TextBackendSimple (FontManager &fontManager, Registry &registry)
	Construct a simple text backend using the provided font manager and ECS registry.
bool	requiresTrustedFontData () const override
	Whether this backend may consume only fonts whose byte provenance is trusted.
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.
Path	glyphOutline (FontHandle font, int glyphIndex, float scale, bool allowSyntheticOblique) const override
	Extract an outline with per-glyph synthetic-oblique permission.
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.
ShapedRun	shapeRun (FontHandle font, float fontSizePx, std::string_view spanText, size_t byteOffset, size_t byteLength, bool isVertical, TextOrientation textOrientation, FontVariant fontVariant, bool forceLogicalOrder) const override
	Shape a range with the resolved vertical text orientation.
ShapedRun	shapeRunNoKerning (FontHandle font, float fontSizePx, std::string_view spanText, size_t byteOffset, size_t byteLength, bool isVertical, FontVariant fontVariant, bool forceLogicalOrder) const override
	Shape text with kerning disabled. Backends that cannot selectively disable kerning retain their normal shaping behavior.
ShapedRun	shapeRunNoKerning (FontHandle font, float fontSizePx, std::string_view spanText, size_t byteOffset, size_t byteLength, bool isVertical, TextOrientation textOrientation, FontVariant fontVariant, bool forceLogicalOrder) const override
	Shape orientation-aware text with kerning disabled.
ShapedRun	shapeRunInContext (FontHandle font, float fontSizePx, std::string_view spanText, const ShapingContext &context, size_t byteOffset, size_t byteLength, bool isVertical, TextOrientation textOrientation, FontVariant fontVariant, bool kerning) const override
	Shape [`byteOffset`, `byteOffset` + `byteLength`) as one part of `context`, such as one face's share of a chunk drawn with several faces.
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.
double	crossSpanKern (FontHandle prevFont, float prevSizePx, FontHandle curFont, float curSizePx, uint32_t prevCodepoint, uint32_t curCodepoint, bool isVertical, TextOrientation textOrientation) const override
	Compute cross-span kerning with the resolved vertical orientation.
double	crossSpanKern (FontHandle previousFont, float previousSize, FontHandle currentFont, float currentSize, uint32_t previousCodepoint, uint32_t currentCodepoint, bool vertical, TextOrientation orientation, const ShapingContext &context) const override
	Resolve a visual neighboring pair inside one shared directional shaping context.
Public Member Functions inherited from donner::svg::TextBackend
virtual std::optional< BitmapGlyphMetrics >	bitmapGlyphMetrics (FontHandle font, int glyphIndex, float scale) const
	Query bounded bitmap metadata without materializing bitmap pixels.
virtual std::optional< BitmapGlyph >	bitmapGlyph (FontHandle font, int glyphIndex, float scale, const BitmapGlyphMetrics &admitted, std::size_t maximumRgbaBytes) const
	Decode only after independently revalidating admitted metrics and the RGBA byte limit. This bounds converted RGBA storage, not every internal decoder allocation.
virtual double	crossSpanKernNoKerning (FontHandle, float, FontHandle, float, uint32_t, uint32_t, bool) const
	Compute cross-span kerning with kerning disabled.

Detailed Description

stb_truetype-based font backend.

Provides font metrics, glyph outlines, and table-derived data using stb_truetype. No GSUB/GPOS shaping, no bitmap glyph support, no cursive script detection.

Member Function Documentation

◆ bitmapGlyph()

std::optional< BitmapGlyph > donner::svg::TextBackendSimple::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() [1/3]

double donner::svg::TextBackendSimple::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.

◆ crossSpanKern() [2/3]

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

overridevirtual

Compute cross-span kerning with the resolved vertical orientation.

Reimplemented from donner::svg::TextBackend.

◆ crossSpanKern() [3/3]

double donner::svg::TextBackendSimple::crossSpanKern	(	FontHandle	previousFont,
		float	previousSize,
		FontHandle	currentFont,
		float	currentSize,
		uint32_t	previousCodepoint,
		uint32_t	currentCodepoint,
		bool	vertical,
		TextOrientation	orientation,
		const ShapingContext &	context ) const

overridevirtual

Resolve a visual neighboring pair inside one shared directional shaping context.

Reimplemented from donner::svg::TextBackend.

◆ fontVMetrics()

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

overridevirtual

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

Implements donner::svg::TextBackend.

◆ glyphOutline() [1/2]

Path donner::svg::TextBackendSimple::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.

◆ glyphOutline() [2/2]

Path donner::svg::TextBackendSimple::glyphOutline	(	FontHandle	font,
		int	glyphIndex,
		float	scale,
		bool	allowSyntheticOblique ) const

overridevirtual

Extract an outline with per-glyph synthetic-oblique permission.

Parameters

font	Face whose glyph is extracted.
glyphIndex	Glyph index in the face.
scale	Font-unit to pixel scale.
allowSyntheticOblique	Whether a synthesized oblique transform may be applied.

Returns: The glyph outline; native styles and variable axes are always preserved.

Reimplemented from donner::svg::TextBackend.

◆ hasSmallCapsFeature()

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

overridevirtual

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

Implements donner::svg::TextBackend.

◆ isCursive()

bool donner::svg::TextBackendSimple::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.

◆ requiresTrustedFontData()

bool donner::svg::TextBackendSimple::requiresTrustedFontData ( ) const

inlineoverridevirtual

Whether this backend may consume only fonts whose byte provenance is trusted.

Reimplemented from donner::svg::TextBackend.

◆ scaleForEmToPixels()

float donner::svg::TextBackendSimple::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::TextBackendSimple::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() [1/2]

ShapedRun donner::svg::TextBackendSimple::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.

◆ shapeRun() [2/2]

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

overridevirtual

Shape a range with the resolved vertical text orientation.

Reimplemented from donner::svg::TextBackend.

◆ shapeRunInContext()

ShapedRun donner::svg::TextBackendSimple::shapeRunInContext	(	FontHandle	font,
		float	fontSizePx,
		std::string_view	spanText,
		const ShapingContext &	context,
		size_t	byteOffset,
		size_t	byteLength,
		bool	isVertical,
		TextOrientation	textOrientation,
		FontVariant	fontVariant,
		bool	kerning ) const

overridevirtual

Shape [byteOffset, byteOffset + byteLength) as one part of context, such as one face's share of a chunk drawn with several faces.

A context-aware backend shapes the range with the surrounding characters as pre- and post-context and picks its direction, script and language as follows:

A range with no script of its own (punctuation, spaces, symbols) takes the context's direction, script and language, so neutrals mirror and order like their neighbors. When such a range contains decimal digits in a horizontal context, it keeps the context's script and language but runs left to right, as numbers do in right-to-left text.
A strong left-to-right range inside a vertically shaped context is shaped vertically.
A strong right-to-left range keeps its own horizontal direction.

A context no longer than the range adds nothing, and the range is shaped as by shapeRun. Other backends shape the range alone. Glyph clusters are byte offsets into spanText, as for shapeRun.

Parameters

font	Font to shape with.
fontSizePx	Font size in pixels.
spanText	Full span text (UTF-8).
context	Range of `spanText` that contains the shaped range.
byteOffset	Start of the range to shape within `spanText`.
byteLength	Length of the range to shape.
isVertical	True for vertical writing mode.
textOrientation	Resolved vertical text orientation.
fontVariant	Font variant (Normal or SmallCaps).
kerning	False to shape with kerning disabled.

Reimplemented from donner::svg::TextBackend.

◆ shapeRunNoKerning() [1/2]

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

overridevirtual

Shape text with kerning disabled. Backends that cannot selectively disable kerning retain their normal shaping behavior.

Reimplemented from donner::svg::TextBackend.

◆ shapeRunNoKerning() [2/2]

ShapedRun donner::svg::TextBackendSimple::shapeRunNoKerning	(	FontHandle	font,
		float	fontSizePx,
		std::string_view	spanText,
		size_t	byteOffset,
		size_t	byteLength,
		bool	isVertical,
		TextOrientation	textOrientation,
		FontVariant	fontVariant,
		bool	forceLogicalOrder ) const

overridevirtual

Shape orientation-aware text with kerning disabled.

Reimplemented from donner::svg::TextBackend.

◆ strikeoutMetrics()

std::optional< UnderlineMetrics > donner::svg::TextBackendSimple::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::TextBackendSimple::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::TextBackendSimple::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 file:

donner/svg/text/TextBackendSimple.h

Public Member Functions

Detailed Description

Member Function Documentation

◆ bitmapGlyph()

◆ crossSpanKern() [1/3]

◆ crossSpanKern() [2/3]

◆ crossSpanKern() [3/3]

◆ fontVMetrics()

◆ glyphOutline() [1/2]

◆ glyphOutline() [2/2]

◆ hasSmallCapsFeature()

◆ isBitmapOnly()

◆ isCursive()

◆ requiresTrustedFontData()

◆ scaleForEmToPixels()

◆ scaleForPixelHeight()

◆ shapeRun() [1/2]

◆ shapeRun() [2/2]

◆ shapeRunInContext()

◆ shapeRunNoKerning() [1/2]

◆ shapeRunNoKerning() [2/2]

◆ strikeoutMetrics()

◆ subSuperMetrics()

◆ underlineMetrics()