The QgsLabelingEngine class provides map labeling functionality. The input for the engine is a list of label provider objects and map settings. Based on the input, the engine computes layout of labels for the given map view with no collisions between the labels. Drawing of resulting labels is done again by label providers. More...

#include <qgslabelingengine.h>

Inheritance diagram for QgsLabelingEngine:

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Public Member Functions
	QgsLabelingEngine ()
	Construct the labeling engine with default settings. More...

	QgsLabelingEngine (const QgsLabelingEngine &rh)=delete
	QgsLabelingEngine cannot be copied. More...

virtual	~QgsLabelingEngine ()
	Clean up everything (especially the registered providers) More...

void	addProvider (QgsAbstractLabelProvider *provider)
	Add provider of label features. Takes ownership of the provider. More...

const QgsLabelingEngineSettings &	engineSettings () const
	Gets associated labeling engine settings. More...

const QgsMapSettings &	mapSettings () const
	Gets associated map settings. More...

QgsLabelingEngine &	operator= (const QgsLabelingEngine &rh)=delete
	QgsLabelingEngine cannot be copied. More...

QStringList	participatingLayerIds () const
	Returns a list of layer IDs for layers with providers in the engine. More...

QList< QgsMapLayer * >	participatingLayers () const
	Returns a list of layers with providers in the engine. More...

void	removeProvider (QgsAbstractLabelProvider *provider)
	Remove provider if the provider's initialization failed. Provider instance is deleted. More...

QgsLabelingResults *	results () const
	For internal use by the providers. More...

virtual void	run (QgsRenderContext &context)=0
	Runs the labeling job. More...

void	setMapSettings (const QgsMapSettings &mapSettings)
	Associate map settings instance. More...

QgsLabelingResults *	takeResults ()
	Returns pointer to recently computed results and pass the ownership of results to the caller. More...

Protected Member Functions
void	cleanup ()
	Cleans up the engine following a call to registerLabels() or solve(). More...

void	drawLabels (QgsRenderContext &context, const QString &layerId=QString())
	Draws labels to the specified render context. More...

void	processProvider (QgsAbstractLabelProvider *provider, QgsRenderContext &context, pal::Pal &p)

void	registerLabels (QgsRenderContext &context)
	Runs the label registration step. More...

void	solve (QgsRenderContext &context)
	Solves the label problem. More...

Protected Attributes
QList< pal::LabelPosition * >	mLabels

QgsMapSettings	mMapSettings
	Associated map settings instance. More...

std::unique_ptr< pal::Pal >	mPal

std::unique_ptr< pal::Problem >	mProblem

QList< QgsAbstractLabelProvider * >	mProviders
	List of providers (the are owned by the labeling engine) More...

std::unique_ptr< QgsLabelingResults >	mResults
	Resulting labeling layout. More...

QList< QgsAbstractLabelProvider * >	mSubProviders

QList< pal::LabelPosition * >	mUnlabeled

Detailed Description

The QgsLabelingEngine class provides map labeling functionality. The input for the engine is a list of label provider objects and map settings. Based on the input, the engine computes layout of labels for the given map view with no collisions between the labels. Drawing of resulting labels is done again by label providers.

The labeling engine is used for the map rendering in QgsMapRendererJob instances, individual map layer renderers may add label providers - for example, QgsVectorLayerRenderer may add text label provider and diagram provider (if labeling / diagrams were configured for such vector layer).

The labeling engine may also be used independently from map rendering loop:

QgsLabelingEngine engine;
engine.setMapSettings( mapSettings );
// add one or more providers
engine.addProvider( ... );
// compute the labeling and draw labels (using painter from the context)
engine.run( context );

Note: this class is not a part of public API yet. The provider's interface still uses pal::LabelPosition as an argument in drawLabels() method - this should be sorted out first (a class common to API and pal?). Also, the API may need more polishing to be easy to use - e.g. use concept of labeling layers in API (equivalent of pal::Layer) instead of subProviders(), label providers integrated into feature loop vs providers with independent feature loop), split labeling computation from drawing of labels, improved results class with label iterator).; not available in Python bindings

Since: QGIS 2.12

Definition at line 214 of file qgslabelingengine.h.

Constructor & Destructor Documentation

◆ QgsLabelingEngine() [1/2]

QgsLabelingEngine::QgsLabelingEngine ( )

Construct the labeling engine with default settings.

Definition at line 79 of file qgslabelingengine.cpp.

◆ ~QgsLabelingEngine()

QgsLabelingEngine::~QgsLabelingEngine ( )

virtual

Clean up everything (especially the registered providers)

Definition at line 83 of file qgslabelingengine.cpp.

◆ QgsLabelingEngine() [2/2]

QgsLabelingEngine::QgsLabelingEngine ( const QgsLabelingEngine & rh )

delete

QgsLabelingEngine cannot be copied.

Member Function Documentation

◆ addProvider()

void QgsLabelingEngine::addProvider ( QgsAbstractLabelProvider * provider )

Add provider of label features. Takes ownership of the provider.

Definition at line 188 of file qgslabelingengine.cpp.

◆ cleanup()

void QgsLabelingEngine::cleanup ( )

protected

Cleans up the engine following a call to registerLabels() or solve().

Since: QGIS 3.10

Definition at line 521 of file qgslabelingengine.cpp.

◆ drawLabels()

void QgsLabelingEngine::drawLabels	(	QgsRenderContext &	context,
		const QString &	layerId = `QString()`
	)

protected

Draws labels to the specified render context.

If layerId is specified, only labels from the matching layer will be rendered.

Must be preceded by a call to registerLabels() and solve()

Since: QGIS 3.10

Definition at line 401 of file qgslabelingengine.cpp.

◆ engineSettings()

const QgsLabelingEngineSettings& QgsLabelingEngine::engineSettings ( ) const

inline

Gets associated labeling engine settings.

Definition at line 233 of file qgslabelingengine.h.

◆ mapSettings()

const QgsMapSettings& QgsLabelingEngine::mapSettings ( ) const

inline

Gets associated map settings.

Definition at line 230 of file qgslabelingengine.h.

◆ operator=()

QgsLabelingEngine& QgsLabelingEngine::operator= ( const QgsLabelingEngine & rh )

delete

QgsLabelingEngine cannot be copied.

◆ participatingLayerIds()

QStringList QgsLabelingEngine::participatingLayerIds ( ) const

Returns a list of layer IDs for layers with providers in the engine.

Since: QGIS 3.10

Definition at line 142 of file qgslabelingengine.cpp.

◆ participatingLayers()

QList< QgsMapLayer * > QgsLabelingEngine::participatingLayers ( ) const

Returns a list of layers with providers in the engine.

Since: QGIS 3.0

Definition at line 96 of file qgslabelingengine.cpp.

◆ processProvider()

void QgsLabelingEngine::processProvider	(	QgsAbstractLabelProvider *	provider,
		QgsRenderContext &	context,
		pal::Pal &	p
	)

protected

Definition at line 203 of file qgslabelingengine.cpp.

◆ registerLabels()

void QgsLabelingEngine::registerLabels ( QgsRenderContext & context )

protected

Runs the label registration step.

Must be called by subclasses prior to solve() and drawLabels()

Since: QGIS 3.10

Definition at line 267 of file qgslabelingengine.cpp.

◆ removeProvider()

void QgsLabelingEngine::removeProvider ( QgsAbstractLabelProvider * provider )

Remove provider if the provider's initialization failed. Provider instance is deleted.

Definition at line 194 of file qgslabelingengine.cpp.

◆ results()

QgsLabelingResults* QgsLabelingEngine::results ( ) const

inline

For internal use by the providers.

Definition at line 266 of file qgslabelingengine.h.

◆ run()

virtual void QgsLabelingEngine::run ( QgsRenderContext & context )

pure virtual

Runs the labeling job.

Depending on the concrete labeling engine class, this will either run the whole labeling job, including rendering the labels themselves, OR possibly just run the labeling job but leave the rendering to a future, deferred stage.

Implemented in QgsStagedRenderLabelingEngine, and QgsDefaultLabelingEngine.

◆ setMapSettings()

void QgsLabelingEngine::setMapSettings ( const QgsMapSettings & mapSettings )

Associate map settings instance.

Definition at line 89 of file qgslabelingengine.cpp.

◆ solve()

void QgsLabelingEngine::solve ( QgsRenderContext & context )

protected

Solves the label problem.

Must be called by subclasses prior to drawLabels(), and must be preceded by a call to registerLabels()

Since: QGIS 3.10

Definition at line 291 of file qgslabelingengine.cpp.

◆ takeResults()

QgsLabelingResults * QgsLabelingEngine::takeResults ( )

Returns pointer to recently computed results and pass the ownership of results to the caller.

Definition at line 529 of file qgslabelingengine.cpp.

Member Data Documentation

◆ mLabels

QList<pal::LabelPosition *> QgsLabelingEngine::mLabels

protected

Definition at line 323 of file qgslabelingengine.h.

◆ mMapSettings

QgsMapSettings QgsLabelingEngine::mMapSettings

protected

Associated map settings instance.

Definition at line 311 of file qgslabelingengine.h.

◆ mPal

std::unique_ptr< pal::Pal > QgsLabelingEngine::mPal

protected

Definition at line 320 of file qgslabelingengine.h.

◆ mProblem

std::unique_ptr< pal::Problem > QgsLabelingEngine::mProblem

protected

Definition at line 321 of file qgslabelingengine.h.

◆ mProviders

QList<QgsAbstractLabelProvider *> QgsLabelingEngine::mProviders

protected

List of providers (the are owned by the labeling engine)

Definition at line 314 of file qgslabelingengine.h.

◆ mResults

std::unique_ptr< QgsLabelingResults > QgsLabelingEngine::mResults

protected

Resulting labeling layout.

Definition at line 318 of file qgslabelingengine.h.

◆ mSubProviders

QList<QgsAbstractLabelProvider *> QgsLabelingEngine::mSubProviders

protected

Definition at line 315 of file qgslabelingengine.h.

◆ mUnlabeled

QList<pal::LabelPosition *> QgsLabelingEngine::mUnlabeled

protected

Definition at line 322 of file qgslabelingengine.h.

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

/build/qgis-3.14.0+99unstable/src/core/labeling/qgslabelingengine.h
/build/qgis-3.14.0+99unstable/src/core/labeling/qgslabelingengine.cpp

Public Member Functions

Protected Member Functions

Protected Attributes

Detailed Description

Constructor & Destructor Documentation

◆ QgsLabelingEngine() [1/2]

◆ ~QgsLabelingEngine()

◆ QgsLabelingEngine() [2/2]

Member Function Documentation

◆ addProvider()

◆ cleanup()

◆ drawLabels()

◆ engineSettings()

◆ mapSettings()

◆ operator=()

◆ participatingLayerIds()

◆ participatingLayers()

◆ processProvider()

◆ registerLabels()

◆ removeProvider()

◆ results()

◆ run()

◆ setMapSettings()

◆ solve()

◆ takeResults()

Member Data Documentation

◆ mLabels

◆ mMapSettings

◆ mPal

◆ mProblem

◆ mProviders

◆ mResults

◆ mSubProviders

◆ mUnlabeled