The QgsVectorLayerLabelProvider class implements a label provider for vector layers. More...

#include <qgsvectorlayerlabelprovider.h>

Inheritance diagram for QgsVectorLayerLabelProvider:

Public Member Functions
	QgsVectorLayerLabelProvider (Qgis::GeometryType geometryType, const QgsFields &fields, const QgsCoordinateReferenceSystem &crs, const QString &providerId, const QgsPalLayerSettings settings, QgsMapLayer layer, const QString &layerName=QString())
	Constructor to initialize the provider from any map layer (e.g. vector tile layer)

	QgsVectorLayerLabelProvider (QgsVectorLayer layer, const QString &providerId, bool withFeatureLoop, const QgsPalLayerSettings settings, const QString &layerName=QString())
	Convenience constructor to initialize the provider from given vector layer.

	~QgsVectorLayerLabelProvider () override

void	drawLabel (QgsRenderContext &context, pal::LabelPosition *label) const override
	Draw this label at the position determined by the labeling engine.

void	drawLabelBackground (QgsRenderContext &context, pal::LabelPosition *label) const override
	Draw the background for the specified label.

void	drawUnplacedLabel (QgsRenderContext &context, pal::LabelPosition *label) const override
	Draw an unplaced label.

QList< QgsLabelFeature * >	labelFeatures (QgsRenderContext &context) override
	Returns list of label features (they are owned by the provider and thus deleted on its destruction)

virtual bool	prepare (QgsRenderContext &context, QSet< QString > &attributeNames)
	Prepare for registration of features.

virtual QList< QgsLabelFeature * >	registerFeature (const QgsFeature &feature, QgsRenderContext &context, const QgsGeometry &obstacleGeometry=QgsGeometry(), const QgsSymbol *symbol=nullptr)
	Register a feature for labeling as one or more QgsLabelFeature objects stored into mLabels.

void	setFields (const QgsFields &fields)
	Sets fields of this label provider.

const QgsPalLayerSettings &	settings () const
	Returns the layer's settings.

void	startRender (QgsRenderContext &context) override
	To be called before rendering of labels begins.

void	stopRender (QgsRenderContext &context) override
	To be called after rendering is complete.

Public Member Functions inherited from QgsAbstractLabelProvider
	QgsAbstractLabelProvider (QgsMapLayer *layer, const QString &providerId=QString())
	Construct the provider with default values.

virtual	~QgsAbstractLabelProvider ()=default

Flags	flags () const
	Flags associated with the provider.

QgsMapLayer *	layer () const
	Returns the associated layer, or `nullptr` if no layer is associated with the provider.

QgsExpressionContextScope *	layerExpressionContextScope () const
	Returns the expression context scope created from the layer associated with this provider.

QString	layerId () const
	Returns ID of associated layer, or empty string if no layer is associated with the provider.

double	layerReferenceScale () const
	Returns the symbology reference scale of the layer associated with this provider.

QString	name () const
	Name of the layer (for statistics, debugging etc.) - does not need to be unique.

QgsLabelObstacleSettings::ObstacleType	obstacleType () const
	How the feature geometries will work as obstacles.

Qgis::LabelPlacement	placement () const
	What placement strategy to use for the labels.

double	priority () const
	Default priority of labels (may be overridden by individual labels)

QString	providerId () const
	Returns provider ID - useful in case there is more than one label provider within a layer (e.g.

void	setEngine (const QgsLabelingEngine *engine)
	Associate provider with a labeling engine (should be only called internally from QgsLabelingEngine)

virtual QList< QgsAbstractLabelProvider * >	subProviders ()
	Returns list of child providers - useful if the provider needs to put labels into more layers with different configuration.

Qgis::UpsideDownLabelHandling	upsidedownLabels () const
	How to handle labels that would be upside down.

Static Public Member Functions
static QgsGeometry	getPointObstacleGeometry (QgsFeature &fet, QgsRenderContext &context, const QgsSymbolList &symbols)
	Returns the geometry for a point feature which should be used as an obstacle for labels.

Protected Member Functions
void	drawLabelPrivate (pal::LabelPosition *label, QgsRenderContext &context, QgsPalLayerSettings &tmpLyr, Qgis::TextComponent drawType, double dpiRatio=1.0) const
	Internal label drawing method.

void	init ()
	initialization method - called from constructors

Protected Attributes
QgsCoordinateReferenceSystem	mCrs
	Layer's CRS.

QgsFields	mFields
	Layer's fields.

QList< QgsLabelFeature * >	mLabels
	List of generated.

Qgis::GeometryType	mLayerGeometryType
	Geometry type of layer.

QgsFeatureRenderer *	mRenderer = nullptr

QgsPalLayerSettings	mSettings
	Layer's labeling configuration.

std::unique_ptr< QgsAbstractFeatureSource >	mSource
	Layer's feature source.

Protected Attributes inherited from QgsAbstractLabelProvider
const QgsLabelingEngine *	mEngine = nullptr
	Associated labeling engine.

Flags	mFlags = DrawLabels
	Flags altering drawing and registration of features.

QgsWeakMapLayerPointer	mLayer
	Weak pointer to source layer.

QString	mLayerId
	Associated layer's ID, if applicable.

QString	mName
	Name of the layer.

QgsLabelObstacleSettings::ObstacleType	mObstacleType = QgsLabelObstacleSettings::PolygonBoundary
	Type of the obstacle of feature geometries.

Qgis::LabelPlacement	mPlacement = Qgis::LabelPlacement::AroundPoint
	Placement strategy.

double	mPriority = 0.5
	Default priority of labels.

QString	mProviderId
	Associated provider ID (one layer may have multiple providers, e.g. in rule-based labeling)

Qgis::UpsideDownLabelHandling	mUpsidedownLabels = Qgis::UpsideDownLabelHandling::FlipUpsideDownLabels
	How to handle labels that would be upside down.

Friends
class	QgsVectorTileBasicLabelProvider

class	TestQgsLabelingEngine

Additional Inherited Members
Public Types inherited from QgsAbstractLabelProvider
enum	Flag { DrawLabels = 1 << 1 , MergeConnectedLines = 1 << 3 , CentroidMustBeInside = 1 << 4 }

Detailed Description

The QgsVectorLayerLabelProvider class implements a label provider for vector layers.

Parameters for the labeling are taken from the layer's custom properties or from the given settings.

Note: this class is not a part of public API yet. See notes in QgsLabelingEngine; not available in Python bindings

Since: QGIS 2.12

Definition at line 40 of file qgsvectorlayerlabelprovider.h.

Constructor & Destructor Documentation

◆ QgsVectorLayerLabelProvider() [1/2]

QgsVectorLayerLabelProvider::QgsVectorLayerLabelProvider	(	QgsVectorLayer *	layer,
		const QString &	providerId,
		bool	withFeatureLoop,
		const QgsPalLayerSettings *	settings,
		const QString &	layerName = `QString()`
	)

explicit

Convenience constructor to initialize the provider from given vector layer.

Definition at line 50 of file qgsvectorlayerlabelprovider.cpp.

◆ QgsVectorLayerLabelProvider() [2/2]

QgsVectorLayerLabelProvider::QgsVectorLayerLabelProvider	(	Qgis::GeometryType	geometryType,
		const QgsFields &	fields,
		const QgsCoordinateReferenceSystem &	crs,
		const QString &	providerId,
		const QgsPalLayerSettings *	settings,
		QgsMapLayer *	layer,
		const QString &	layerName = `QString()`
	)

explicit

Constructor to initialize the provider from any map layer (e.g. vector tile layer)

Definition at line 68 of file qgsvectorlayerlabelprovider.cpp.

◆ ~QgsVectorLayerLabelProvider()

QgsVectorLayerLabelProvider::~QgsVectorLayerLabelProvider ( )

override

Definition at line 109 of file qgsvectorlayerlabelprovider.cpp.

Member Function Documentation

◆ drawLabel()

void QgsVectorLayerLabelProvider::drawLabel	(	QgsRenderContext &	context,
		pal::LabelPosition *	label
	)		const

overridevirtual

Draw this label at the position determined by the labeling engine.

Before any calls to drawLabel(), a provider should be prepared for rendering by a call to startRender() and a corresponding call to stopRender().

Implements QgsAbstractLabelProvider.

Definition at line 358 of file qgsvectorlayerlabelprovider.cpp.

◆ drawLabelBackground()

void QgsVectorLayerLabelProvider::drawLabelBackground	(	QgsRenderContext &	context,
		pal::LabelPosition *	label
	)		const

overridevirtual

Draw the background for the specified label.

This is called in turn for each label provider before any actual labels are rendered, and allows the provider to render content which should be drawn below ALL map labels (such as background rectangles or callout lines).

Before any calls to drawLabelBackground(), a provider should be prepared for rendering by a call to startRender() and a corresponding call to stopRender().

Since: QGIS 3.10

Reimplemented from QgsAbstractLabelProvider.

Definition at line 311 of file qgsvectorlayerlabelprovider.cpp.

◆ drawLabelPrivate()

void QgsVectorLayerLabelProvider::drawLabelPrivate	(	pal::LabelPosition *	label,
		QgsRenderContext &	context,
		QgsPalLayerSettings &	tmpLyr,
		Qgis::TextComponent	drawType,
		double	dpiRatio = `1.0`
	)		const

protected

Internal label drawing method.

Definition at line 495 of file qgsvectorlayerlabelprovider.cpp.

◆ drawUnplacedLabel()

void QgsVectorLayerLabelProvider::drawUnplacedLabel	(	QgsRenderContext &	context,
		pal::LabelPosition *	label
	)		const

overridevirtual

Draw an unplaced label.

These correspond to features which were registered for labeling, but which could not be labeled (e.g. due to conflicting labels).

The default behavior is to draw nothing for these labels.

Note: This method is only used if the Qgis::Qgis::LabelingFlag::DrawUnplacedLabels flag is set on the labeling engine.

Since: QGIS 3.10

Reimplemented from QgsAbstractLabelProvider.

Definition at line 474 of file qgsvectorlayerlabelprovider.cpp.

◆ getPointObstacleGeometry()

QgsGeometry QgsVectorLayerLabelProvider::getPointObstacleGeometry	(	QgsFeature &	fet,
		QgsRenderContext &	context,
		const QgsSymbolList &	symbols
	)

static

Returns the geometry for a point feature which should be used as an obstacle for labels.

This obstacle geometry will respect the dimensions and offsets of the symbol used to render the point, and ensures that labels will not overlap large or offset points.

Parameters

fet	point feature
context	render context
symbols	symbols rendered for point feature

Since: QGIS 2.14

Definition at line 209 of file qgsvectorlayerlabelprovider.cpp.

◆ init()

void QgsVectorLayerLabelProvider::init ( )

protected

initialization method - called from constructors

Definition at line 81 of file qgsvectorlayerlabelprovider.cpp.

◆ labelFeatures()

QList< QgsLabelFeature * > QgsVectorLayerLabelProvider::labelFeatures ( QgsRenderContext & context )

overridevirtual

Returns list of label features (they are owned by the provider and thus deleted on its destruction)

Implements QgsAbstractLabelProvider.

Definition at line 134 of file qgsvectorlayerlabelprovider.cpp.

◆ prepare()

bool QgsVectorLayerLabelProvider::prepare	(	QgsRenderContext &	context,
		QSet< QString > &	attributeNames
	)

virtual

Prepare for registration of features.

Must be called after provider has been added to engine (uses its map settings)

Parameters

context	render context.
attributeNames	list of attribute names to which additional required attributes shall be added

Returns: Whether the preparation was successful - if not, the provider shall not be used

Reimplemented in QgsRuleBasedLabelProvider, and QgsVectorTileBasicLabelProvider.

Definition at line 115 of file qgsvectorlayerlabelprovider.cpp.

◆ registerFeature()

QList< QgsLabelFeature * > QgsVectorLayerLabelProvider::registerFeature	(	const QgsFeature &	feature,
		QgsRenderContext &	context,
		const QgsGeometry &	obstacleGeometry = `QgsGeometry()`,
		const QgsSymbol *	symbol = `nullptr`
	)

virtual

Register a feature for labeling as one or more QgsLabelFeature objects stored into mLabels.

Parameters

feature	feature to label
context	render context. The QgsExpressionContext contained within the render context must have already had the feature and fields sets prior to calling this method.
obstacleGeometry	optional obstacle geometry, if a different geometry to the feature's geometry should be used as an obstacle for labels (e.g., if the feature has been rendered with an offset point symbol, the obstacle geometry should represent the bounds of the offset symbol). If not set, the feature's original geometry will be used as an obstacle for labels.
symbol	feature symbol to label (ownership is not transferred - the symbol must exist until after labeling is complete)

Returns: a list of the newly generated label features. Ownership of these label features is not transferred (it has already been assigned to the label provider).

Reimplemented in QgsRuleBasedLabelProvider.

Definition at line 197 of file qgsvectorlayerlabelprovider.cpp.

◆ setFields()

void QgsVectorLayerLabelProvider::setFields ( const QgsFields & fields )

Sets fields of this label provider.

Normally this is not needed, but when used for vector tiles, fields are not known at the time of creation of label providers. It should be called before a call to prepare() which uses the list of fields.