QgsLabelingEngine Class Reference

The QgsLabelingEngine class provides map labeling functionality. More...

#include <qgslabelingengine.h>

Public Member Functions
	QgsLabelingEngine ()
	Construct the labeling engine with default settings. More...
	QgsLabelingEngine (const QgsLabelingEngine &rh)=delete
	QgsLabelingEngine cannot be copied. More...
	~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...
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...
void	run (QgsRenderContext &context)
	compute the labeling with given map settings and providers 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	processProvider (QgsAbstractLabelProvider *provider, QgsRenderContext &context, pal::Pal &p)

Protected Attributes
QgsMapSettings	mMapSettings
	Associated map settings instance. More...
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

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 165 of file qgslabelingengine.h.

Constructor & Destructor Documentation

QgsLabelingEngine::QgsLabelingEngine

(

)

Construct the labeling engine with default settings.

Definition at line 74 of file qgslabelingengine.cpp.

QgsLabelingEngine::~QgsLabelingEngine

(

)

Clean up everything (especially the registered providers)

Definition at line 78 of file qgslabelingengine.cpp.

QgsLabelingEngine::QgsLabelingEngine ( const QgsLabelingEngine &  rh )

delete

QgsLabelingEngine cannot be copied.

Member Function Documentation

void QgsLabelingEngine::addProvider

(

QgsAbstractLabelProvider *

provider

)

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

Definition at line 107 of file qgslabelingengine.cpp.

const QgsLabelingEngineSettings& QgsLabelingEngine::engineSettings ( ) const

inline

Gets associated labeling engine settings.

Definition at line 184 of file qgslabelingengine.h.

const QgsMapSettings& QgsLabelingEngine::mapSettings ( ) const

inline

Gets associated map settings.

Definition at line 181 of file qgslabelingengine.h.

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

delete

QgsLabelingEngine cannot be copied.

QList< QgsMapLayer * > QgsLabelingEngine::participatingLayers

(

)

const

Returns a list of layers with providers in the engine.

Since

QGIS 3.0

Definition at line 91 of file qgslabelingengine.cpp.

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

protected

Definition at line 122 of file qgslabelingengine.cpp.

void QgsLabelingEngine::removeProvider

(

QgsAbstractLabelProvider *

provider

)

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

Definition at line 113 of file qgslabelingengine.cpp.

QgsLabelingResults* QgsLabelingEngine::results ( ) const

inline

For internal use by the providers.

Definition at line 205 of file qgslabelingengine.h.

void QgsLabelingEngine::run

(

QgsRenderContext &

context

)

compute the labeling with given map settings and providers

Definition at line 192 of file qgslabelingengine.cpp.

void QgsLabelingEngine::setMapSettings

(

const QgsMapSettings &

mapSettings

)

Associate map settings instance.

Definition at line 84 of file qgslabelingengine.cpp.

QgsLabelingResults * QgsLabelingEngine::takeResults

(

)

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

Definition at line 352 of file qgslabelingengine.cpp.

Member Data Documentation

QgsMapSettings QgsLabelingEngine::mMapSettings

protected

Associated map settings instance.

Definition at line 212 of file qgslabelingengine.h.

QList<QgsAbstractLabelProvider *> QgsLabelingEngine::mProviders

protected

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

Definition at line 215 of file qgslabelingengine.h.

std::unique_ptr< QgsLabelingResults > QgsLabelingEngine::mResults

protected

Resulting labeling layout.

Definition at line 219 of file qgslabelingengine.h.

QList<QgsAbstractLabelProvider *> QgsLabelingEngine::mSubProviders

protected

Definition at line 216 of file qgslabelingengine.h.

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

• /build/qgis-3.4.15+24xenial/src/core/qgslabelingengine.h
• /build/qgis-3.4.15+24xenial/src/core/qgslabelingengine.cpp