Internal helpers for TextEngine layout. Exposed in a header for unit testing. More...

#include <cstddef>
#include <cstdint>
#include <optional>
#include <span>
#include <string_view>
#include <utility>
#include <vector>
#include "donner/base/Length.h"
#include "donner/base/MathUtils.h"
#include "donner/base/SmallVector.h"
#include "donner/base/Transform.h"
#include "donner/svg/components/text/ComputedTextComponent.h"
#include "donner/svg/core/DominantBaseline.h"
#include "donner/svg/core/TextAnchor.h"
#include "donner/svg/text/TextBackend.h"
#include "donner/svg/text/TextLayoutParams.h"
#include "donner/svg/text/TextTypes.h"

Include dependency graph for TextEngineHelpers.h:

Classes
struct	donner::svg::text_engine_detail::ChunkRange
	Byte range within a span representing a shaping chunk. More...
struct	donner::svg::text_engine_detail::ByteIndexMappings
	Index mapping result for a span's text. More...
struct	donner::svg::text_engine_detail::ChunkBoundary
	Text chunk boundary for per-chunk text-anchor adjustment. More...
struct	donner::svg::text_engine_detail::InlineDisplacement
	An authored inline displacement consumed by one positioned glyph group. More...
struct	donner::svg::text_engine_detail::RunPenExtent
	Per-run pen start/end position for textLength calculation. More...
struct	donner::svg::text_engine_detail::TextLengthTraversalStats
	Optional operation counts for deterministic textLength traversal complexity tests. More...

Namespaces
namespace	donner
	Top-level Donner namespace, which is split into different sub-namespaces such as donner::svg and donner::css.
namespace	donner::svg
	Donner SVG library, which can load, manipulate and render SVG files.

Typedefs
using	donner::svg::text_engine_detail::AnchorExclusions = std::vector<std::vector<bool>>
	Per-run masks indexed by original source-byte cluster, retaining CSS hanging decisions through SVG textLength adjustments and glyph quarantine. Empty runs have no excluded clusters.

Functions
template<typename Bitmap>
Transform2d	donner::svg::text_engine_detail::computeLocalFromBitmapGlyph (const TextGlyph &glyph, const Bitmap &bitmap)
	Map positive-size bitmap texels through their bearing and stretch, then rotate at glyph origin.
double	donner::svg::text_engine_detail::computeBaselineShift (DominantBaseline baseline, const FontVMetrics &vm, float scale)
	Compute the baseline-alignment offset for a dominant-baseline / alignment-baseline keyword, in pixels. The offset is added to the baseline Y position, so positive values move glyphs down (+Y in SVG coordinates); e.g. hanging returns +0.8 * ascent.
std::vector< ChunkRange >	donner::svg::text_engine_detail::findChunkRanges (std::string_view spanText, const SmallVector< std::optional< Lengthd >, 1 > &xList, const SmallVector< std::optional< Lengthd >, 1 > &yList)
	Pre-scan span text to find chunk byte boundaries. A new chunk starts when a non-first typographic character has an absolute x or y position.
ByteIndexMappings	donner::svg::text_engine_detail::buildByteIndexMappings (std::string_view spanText)
	Build the byte-to-codepoint map; shaping determines group applicability. DOM indexing is separate.
void	donner::svg::text_engine_detail::applyTextLength (std::vector< TextRun > &runs, const components::ComputedTextComponent &text, const std::vector< RunPenExtent > &runExtents, const TextLayoutParams &params, bool vertical, double currentPenX, double currentPenY, TextLengthTraversalStats *traversalStats=nullptr)
	Apply per-span and global textLength adjustments to positioned runs.
void	donner::svg::text_engine_detail::applyTextAnchor (std::vector< TextRun > &runs, std::vector< ChunkBoundary > &chunkBoundaries, const components::ComputedTextComponent &text, bool vertical, const AnchorExclusions &exclusions={}, double firstLineIndent=0.0)
	Fix up chunk anchors and apply the existing per-line anchor profile. firstLineIndent contributes its signed leading margin only to the first flat chunk.
bool	donner::svg::text_engine_detail::applyInlineSizeWrap (std::vector< TextRun > &runs, const components::ComputedTextComponent &text, const TextLayoutParams &params, double measurePx, double lineHeightPx, const TextBackend backend=nullptr, std::span< const ChunkBoundary > chunks={}, std::span< const InlineDisplacement > displacements={}, AnchorExclusions exclusions=nullptr)
	Apply whitespace-dependent line layout along the inline axis, before text-anchor adjustment. Each line/chunk uses its first addressable character's anchor; lines advance along the block axis.
double	donner::svg::text_engine_detail::computeSpanBaselineShiftPx (const TextBackend &backend, const components::ComputedTextComponent::TextSpan &span, FontHandle spanFont, float spanScale, const TextLayoutParams &params)
	Compute per-span baseline-shift in pixels, including OS/2 sub/super metrics and ancestor baseline-shift accumulation.

Detailed Description

Internal helpers for TextEngine layout. Exposed in a header for unit testing.

Function Documentation

◆ applyInlineSizeWrap()

bool donner::svg::text_engine_detail::applyInlineSizeWrap	(	std::vector< TextRun > &	runs,
		const components::ComputedTextComponent &	text,
		const TextLayoutParams &	params,
		double	measurePx,
		double	lineHeightPx,
		const TextBackend *	backend = nullptr,
		std::span< const ChunkBoundary >	chunks = {},
		std::span< const InlineDisplacement >	displacements = {},
		AnchorExclusions *	exclusions = nullptr )

Apply whitespace-dependent line layout along the inline axis, before text-anchor adjustment. Each line/chunk uses its first addressable character's anchor; lines advance along the block axis.

Soft wrapping uses spaces and tabs according to each span's white-space policy. Preserved segment breaks force new lines even without inline-size. Overflow-wrap enables bounded emergency typographic-unit breaks; there is no hyphenation or CJK per-character policy. Collapsible trailing spaces are removed; pre-wrap spaces may hang, while break-spaces gives each preserved space a break opportunity. Text-on-path runs are excluded: their controls are shaped as blanks without creating line boxes.

Parameters

runs	Runs produced by the single-line layout; glyph positions are rewritten.
text	Computed text tree, parallel to `runs` (span i corresponds to run i).
params	Layout params, including writing mode and the first-line start margin.
measurePx	The inline-size measure in pixels, or zero to apply only forced breaks/tabs.
lineHeightPx	Advance between line baselines along the block axis, in pixels.
backend	Font metrics for the minimum tab advance (0.5ch).
chunks	Authored text chunk boundaries, retained across line breaks.
displacements	Per-group authored inline shifts, applied after CSS line layout.
exclusions	Receives source-cluster hanging decisions for final single-line anchoring.

Returns: true if multiple lines were laid out. Tab-only changes return false.

◆ computeBaselineShift()

double donner::svg::text_engine_detail::computeBaselineShift	(	DominantBaseline	baseline,
		const FontVMetrics &	vm,
		float	scale )

Compute the baseline-alignment offset for a dominant-baseline / alignment-baseline keyword, in pixels. The offset is added to the baseline Y position, so positive values move glyphs down (+Y in SVG coordinates); e.g. hanging returns +0.8 * ascent.

Parameters

baseline	Effective baseline keyword for the span.
vm	Font vertical metrics in design units (FontVMetrics::xHeight may be 0).
scale	Design units → pixels scale (em scale, fontSize / unitsPerEm).

◆ computeLocalFromBitmapGlyph()

template<typename Bitmap>

Transform2d donner::svg::text_engine_detail::computeLocalFromBitmapGlyph	(	const TextGlyph &	glyph,
		const Bitmap &	bitmap )

Map positive-size bitmap texels through their bearing and stretch, then rotate at glyph origin.

Parameters

glyph	Placed glyph in text-element local coordinates.
bitmap	Decoded bitmap or metadata with positive width and height.

Returns: Transform from bitmap texels to text-element local coordinates.

Classes

Namespaces

Typedefs

Functions

Detailed Description

Function Documentation

◆ applyInlineSizeWrap()

◆ computeBaselineShift()

◆ computeLocalFromBitmapGlyph()