QGIS API Documentation 3.40.0-Bratislava (b56115d8743)
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Public Member Functions | Protected Member Functions | List of all members
QgsAbstractLabelingEngineRule Class Referenceabstract

Abstract base class for labeling engine rules. More...

#include <qgslabelingenginerule.h>

Inheritance diagram for QgsAbstractLabelingEngineRule:
Inheritance graph
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Public Member Functions

virtual ~QgsAbstractLabelingEngineRule ()
 
bool active () const
 Returns true if the rule is active.
 
virtual void alterCandidateCost (pal::LabelPosition *candidate, QgsLabelingEngineContext &context) const
 Provides an opportunity for the rule to alter the cost for a candidate.
 
virtual bool candidateIsIllegal (const pal::LabelPosition *candidate, QgsLabelingEngineContext &context) const
 Returns true if a labeling candidate violates the rule and should be eliminated.
 
virtual bool candidatesAreConflicting (const pal::LabelPosition *lp1, const pal::LabelPosition *lp2) const
 Returns true if a labeling candidate lp1 conflicts with lp2 after applying the rule.
 
virtual QgsAbstractLabelingEngineRuleclone () const =0
 Creates a clone of this rule.
 
virtual QString description () const
 Returns a user-friendly description of the rule.
 
virtual QString displayType () const =0
 Returns a user-friendly, translated string representing the rule type.
 
virtual QString id () const =0
 Returns a string uniquely identifying the rule subclass.
 
virtual bool isAvailable () const
 Returns true if the rule is available for use within the current QGIS environment.
 
virtual QgsRectangle modifyCandidateConflictSearchBoundingBox (const QgsRectangle &candidateBounds) const
 Returns a (possibly expanded) bounding box to use when searching for conflicts for a candidate.
 
QString name () const
 Returns the name for this instance of the rule.
 
virtual bool prepare (QgsRenderContext &context)=0
 Prepares the rule.
 
virtual void readXml (const QDomElement &element, const QgsReadWriteContext &context)=0
 Reads the rule properties from an XML element.
 
virtual void resolveReferences (const QgsProject *project)
 Resolves reference to layers from stored layer ID.
 
void setActive (bool active)
 Sets whether the rule is active.
 
void setName (const QString &name)
 Sets the name for this instance of the rule.
 
virtual void writeXml (QDomDocument &doc, QDomElement &element, const QgsReadWriteContext &context) const =0
 Writes the rule properties to an XML element.
 

Protected Member Functions

virtual void copyCommonProperties (QgsAbstractLabelingEngineRule *other) const
 Copies common properties from this object to an other.
 

Detailed Description

Abstract base class for labeling engine rules.

Labeling engine rules implement custom logic to modify the labeling solution for a map render, e.g. by preventing labels being placed which violate custom constraints.

Note
QgsAbstractLabelingEngineRule cannot be subclassed in Python. Use one of the existing implementations of this class instead.
Since
QGIS 3.40

Definition at line 132 of file qgslabelingenginerule.h.

Constructor & Destructor Documentation

◆ ~QgsAbstractLabelingEngineRule()

QgsAbstractLabelingEngineRule::~QgsAbstractLabelingEngineRule ( )
virtualdefault

Member Function Documentation

◆ active()

bool QgsAbstractLabelingEngineRule::active ( ) const

Returns true if the rule is active.

See also
setActive()

Definition at line 96 of file qgslabelingenginerule.cpp.

◆ alterCandidateCost()

void QgsAbstractLabelingEngineRule::alterCandidateCost ( pal::LabelPosition candidate,
QgsLabelingEngineContext context 
) const
virtual

Provides an opportunity for the rule to alter the cost for a candidate.

The default implementation does nothing.

Reimplemented in QgsAbstractLabelingEngineRuleDistanceFromFeature.

Definition at line 75 of file qgslabelingenginerule.cpp.

◆ candidateIsIllegal()

bool QgsAbstractLabelingEngineRule::candidateIsIllegal ( const pal::LabelPosition candidate,
QgsLabelingEngineContext context 
) const
virtual

Returns true if a labeling candidate violates the rule and should be eliminated.

The default implementation returns false.

Reimplemented in QgsAbstractLabelingEngineRuleDistanceFromFeature, and QgsLabelingEngineRuleAvoidLabelOverlapWithFeature.

Definition at line 70 of file qgslabelingenginerule.cpp.

◆ candidatesAreConflicting()

bool QgsAbstractLabelingEngineRule::candidatesAreConflicting ( const pal::LabelPosition lp1,
const pal::LabelPosition lp2 
) const
virtual

Returns true if a labeling candidate lp1 conflicts with lp2 after applying the rule.

The default implementation returns false.

Reimplemented in QgsLabelingEngineRuleMinimumDistanceLabelToLabel.

Definition at line 60 of file qgslabelingenginerule.cpp.

◆ clone()

virtual QgsAbstractLabelingEngineRule * QgsAbstractLabelingEngineRule::clone ( ) const
pure virtual

◆ copyCommonProperties()

void QgsAbstractLabelingEngineRule::copyCommonProperties ( QgsAbstractLabelingEngineRule other) const
protectedvirtual

Copies common properties from this object to an other.

Reimplemented in QgsAbstractLabelingEngineRuleDistanceFromFeature.

Definition at line 80 of file qgslabelingenginerule.cpp.

◆ description()

QString QgsAbstractLabelingEngineRule::description ( ) const
virtual

Returns a user-friendly description of the rule.

This should include the rule name() if set, and other useful details for users to quickly identify the rule's purpose when shown in a tooltip.

The returned string may contain HTML formatting.

Reimplemented in QgsLabelingEngineRuleMinimumDistanceLabelToFeature, QgsLabelingEngineRuleMaximumDistanceLabelToFeature, QgsLabelingEngineRuleMinimumDistanceLabelToLabel, and QgsLabelingEngineRuleAvoidLabelOverlapWithFeature.

Definition at line 91 of file qgslabelingenginerule.cpp.

◆ displayType()

virtual QString QgsAbstractLabelingEngineRule::displayType ( ) const
pure virtual

◆ id()

virtual QString QgsAbstractLabelingEngineRule::id ( ) const
pure virtual

◆ isAvailable()

bool QgsAbstractLabelingEngineRule::isAvailable ( ) const
virtual

Returns true if the rule is available for use within the current QGIS environment.

The base class method returns true.

Rules can return false if required dependencies are not available, e.g. if a library version is too old for the rule.

Reimplemented in QgsAbstractLabelingEngineRuleDistanceFromFeature, and QgsLabelingEngineRuleMinimumDistanceLabelToLabel.

Definition at line 86 of file qgslabelingenginerule.cpp.

◆ modifyCandidateConflictSearchBoundingBox()

QgsRectangle QgsAbstractLabelingEngineRule::modifyCandidateConflictSearchBoundingBox ( const QgsRectangle candidateBounds) const
virtual

Returns a (possibly expanded) bounding box to use when searching for conflicts for a candidate.

The return value is permitted to grow the bounding box, but may NOT shrink it.

The default implementation returns the same bounds.

Reimplemented in QgsLabelingEngineRuleMinimumDistanceLabelToLabel.

Definition at line 65 of file qgslabelingenginerule.cpp.

◆ name()

QString QgsAbstractLabelingEngineRule::name ( ) const
inline

Returns the name for this instance of the rule.

The name is a user-configurable value which helps them identify and describe the rule within their projects.

See also
setName()

Definition at line 209 of file qgslabelingenginerule.h.

◆ prepare()

virtual bool QgsAbstractLabelingEngineRule::prepare ( QgsRenderContext context)
pure virtual

Prepares the rule.

This must be called on the main render thread, prior to commencing the render operation. Thread sensitive logic (such as creation of feature sources) can be performed in this method.

Implemented in QgsAbstractLabelingEngineRuleDistanceFromFeature, QgsLabelingEngineRuleMinimumDistanceLabelToLabel, and QgsLabelingEngineRuleAvoidLabelOverlapWithFeature.

◆ readXml()

virtual void QgsAbstractLabelingEngineRule::readXml ( const QDomElement &  element,
const QgsReadWriteContext context 
)
pure virtual

◆ resolveReferences()

void QgsAbstractLabelingEngineRule::resolveReferences ( const QgsProject project)
virtual

Resolves reference to layers from stored layer ID.

Should be called following a call readXml().

Reimplemented in QgsAbstractLabelingEngineRuleDistanceFromFeature, QgsLabelingEngineRuleMinimumDistanceLabelToLabel, and QgsLabelingEngineRuleAvoidLabelOverlapWithFeature.

Definition at line 55 of file qgslabelingenginerule.cpp.

◆ setActive()

void QgsAbstractLabelingEngineRule::setActive ( bool  active)

Sets whether the rule is active.

See also
active()

Definition at line 101 of file qgslabelingenginerule.cpp.

◆ setName()

void QgsAbstractLabelingEngineRule::setName ( const QString &  name)
inline

Sets the name for this instance of the rule.

The name is a user-configurable value which helps them identify and describe the rule within their projects.

See also
name()

Definition at line 219 of file qgslabelingenginerule.h.

◆ writeXml()

virtual void QgsAbstractLabelingEngineRule::writeXml ( QDomDocument &  doc,
QDomElement &  element,
const QgsReadWriteContext context 
) const
pure virtual

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