[api] Implementation of labeling engine rules

See qgis/QGIS-Enhancement-Proposals#299

Implements the API framework for setting advanced labeling engine
rules for a project, and implements 4 initial rule types:

- QgsLabelingEngineRuleMinimumDistanceLabelToFeature: prevents labels
  being placed too *close* to features from a different layer
- QgsLabelingEngineRuleMaximumDistanceLabelToFeature: prevents labels
  being placed too *far* from features from a different layer
- QgsLabelingEngineRuleMinimumDistanceLabelToLabel: prevents labels
  being placed too close to labels from a different layer
- QgsLabelingEngineRuleAvoidLabelOverlapWithFeature: prevents labels
  being placed overlapping features from a different layer

(note that the first 3 rules require a build based on GEOS >= 3.10,
they are not available for older GEOS builds)

Also implements a registry for storing available rule classes,
and serialization of rules and configuration in QGIS projects

doc/CMakeLists.txt

@@ -69,6 +69,7 @@ if(WITH_APIDOC)
       ${CMAKE_SOURCE_DIR}/src/core/geometry
       ${CMAKE_SOURCE_DIR}/src/core/gps
       ${CMAKE_SOURCE_DIR}/src/core/labeling
+      ${CMAKE_SOURCE_DIR}/src/core/labeling/rules
       ${CMAKE_SOURCE_DIR}/src/core/layertree
       ${CMAKE_SOURCE_DIR}/src/core/layout
       ${CMAKE_SOURCE_DIR}/src/core/locator

python/PyQt6/core/auto_additions/qgsapplication.py

@@ -135,6 +135,7 @@
 QgsApplication.renderer3DRegistry = staticmethod(QgsApplication.renderer3DRegistry)
 QgsApplication.symbol3DRegistry = staticmethod(QgsApplication.symbol3DRegistry)
 QgsApplication.scaleBarRendererRegistry = staticmethod(QgsApplication.scaleBarRendererRegistry)
+QgsApplication.labelingEngineRuleRegistry = staticmethod(QgsApplication.labelingEngineRuleRegistry)
 QgsApplication.projectStorageRegistry = staticmethod(QgsApplication.projectStorageRegistry)
 QgsApplication.layerMetadataProviderRegistry = staticmethod(QgsApplication.layerMetadataProviderRegistry)
 QgsApplication.externalStorageRegistry = staticmethod(QgsApplication.externalStorageRegistry)

python/PyQt6/core/auto_additions/qgslabelingenginerule.py

@@ -0,0 +1,9 @@
+# The following has been generated automatically from src/core/labeling/rules/qgslabelingenginerule.h
+try:
+    QgsLabelingEngineContext.__group__ = ['labeling', 'rules']
+except NameError:
+    pass
+try:
+    QgsAbstractLabelingEngineRule.__group__ = ['labeling', 'rules']
+except NameError:
+    pass

python/PyQt6/core/auto_additions/qgslabelingenginerule_impl.py

@@ -0,0 +1,21 @@
+# The following has been generated automatically from src/core/labeling/rules/qgslabelingenginerule_impl.h
+try:
+    QgsAbstractLabelingEngineRuleDistanceFromFeature.__group__ = ['labeling', 'rules']
+except NameError:
+    pass
+try:
+    QgsLabelingEngineRuleMinimumDistanceLabelToFeature.__group__ = ['labeling', 'rules']
+except NameError:
+    pass
+try:
+    QgsLabelingEngineRuleMaximumDistanceLabelToFeature.__group__ = ['labeling', 'rules']
+except NameError:
+    pass
+try:
+    QgsLabelingEngineRuleMinimumDistanceLabelToLabel.__group__ = ['labeling', 'rules']
+except NameError:
+    pass
+try:
+    QgsLabelingEngineRuleAvoidLabelOverlapWithFeature.__group__ = ['labeling', 'rules']
+except NameError:
+    pass

python/PyQt6/core/auto_additions/qgslabelingengineruleregistry.py

@@ -0,0 +1,5 @@
+# The following has been generated automatically from src/core/labeling/rules/qgslabelingengineruleregistry.h
+try:
+    QgsLabelingEngineRuleRegistry.__group__ = ['labeling', 'rules']
+except NameError:
+    pass

python/PyQt6/core/auto_generated/labeling/qgslabelingenginesettings.sip.in

@@ -30,6 +30,9 @@ Stores global configuration for labeling engine
     };
 
     QgsLabelingEngineSettings();
+    ~QgsLabelingEngineSettings();
+
+    QgsLabelingEngineSettings( const QgsLabelingEngineSettings &other );
 
     void clear();
 %Docstring
@@ -125,13 +128,66 @@ Which search method to use for removal collisions between labels
    Chain is always used.
 %End
 
+
     void readSettingsFromProject( QgsProject *project );
 %Docstring
 Read configuration of the labeling engine from a project
+
+.. note::
+
+   Both this method and :py:func:`~QgsLabelingEngineSettings.readXml` must be called to completely restore the object's state from a project.
 %End
+
     void writeSettingsToProject( QgsProject *project );
 %Docstring
-Write configuration of the labeling engine to a project
+Write configuration of the labeling engine to a project.
+
+.. note::
+
+   Both this method and :py:func:`~QgsLabelingEngineSettings.writeXml` must be called to completely store the object's state in a project.
+%End
+
+    void writeXml( QDomDocument &doc, QDomElement &element, const QgsReadWriteContext &context ) const;
+%Docstring
+Writes the label engine settings to an XML ``element``.
+
+.. note::
+
+   Both this method and :py:func:`~QgsLabelingEngineSettings.writeSettingsToProject` must be called to completely store the object's state in a project.
+
+.. seealso:: :py:func:`readXml`
+
+.. seealso:: :py:func:`writeSettingsToProject`
+
+.. versionadded:: 3.40
+%End
+
+    void readXml( const QDomElement &element, const QgsReadWriteContext &context );
+%Docstring
+Reads the label engine settings from an XML ``element``.
+
+.. note::
+
+   Both this method and :py:func:`~QgsLabelingEngineSettings.readSettingsFromProject` must be called to completely restore the object's state from a project.
+
+.. note::
+
+   :py:func:`~QgsLabelingEngineSettings.resolveReferences` must be called following this method.
+
+.. seealso:: :py:func:`writeXml`
+
+.. seealso:: :py:func:`readSettingsFromProject`
+
+.. versionadded:: 3.40
+%End
+
+    void resolveReferences( const QgsProject *project );
+%Docstring
+Resolves reference to layers from stored layer ID.
+
+Should be called following a call :py:func:`~QgsLabelingEngineSettings.readXml`.
+
+.. versionadded:: 3.40
 %End
 
 
@@ -187,6 +243,47 @@ Sets the placement engine ``version``, which dictates how the label placement pr
 .. seealso:: :py:func:`placementVersion`
 
 .. versionadded:: 3.10.2
+%End
+
+    QList< QgsAbstractLabelingEngineRule * > rules();
+%Docstring
+Returns a list of labeling engine rules which must be satifisfied
+while placing labels.
+
+.. seealso:: :py:func:`addRule`
+
+.. seealso:: :py:func:`setRules`
+
+.. versionadded:: 3.40
+%End
+
+
+    void addRule( QgsAbstractLabelingEngineRule *rule /Transfer/ );
+%Docstring
+Adds a labeling engine ``rule`` which must be satifisfied
+while placing labels.
+
+Ownership of the rule is transferred to the settings.
+
+.. seealso:: :py:func:`rules`
+
+.. seealso:: :py:func:`setRules`
+
+.. versionadded:: 3.40
+%End
+
+    void setRules( const QList< QgsAbstractLabelingEngineRule * > &rules /Transfer/ );
+%Docstring
+Sets the labeling engine ``rules`` which must be satifisfied
+while placing labels.
+
+Ownership of the rules are transferred to the settings.
+
+.. seealso:: :py:func:`addRule`
+
+.. seealso:: :py:func:`rules`
+
+.. versionadded:: 3.40
 %End
 
 };

python/PyQt6/core/auto_generated/labeling/rules/qgslabelingenginerule.sip.in

@@ -0,0 +1,188 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/labeling/rules/qgslabelingenginerule.h                      *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/
+
+
+
+class QgsLabelingEngineContext
+{
+%Docstring(signature="appended")
+Encapsulates the context for a labeling engine run.
+
+.. versionadded:: 3.40
+%End
+
+%TypeHeaderCode
+#include "qgslabelingenginerule.h"
+%End
+  public:
+
+    QgsLabelingEngineContext( QgsRenderContext &renderContext );
+%Docstring
+Constructor for QgsLabelingEngineContext.
+%End
+
+
+    QgsRenderContext &renderContext();
+%Docstring
+Returns a reference to the context's render context.
+%End
+
+
+    QgsRectangle extent() const;
+%Docstring
+Returns the map extent defining the limits for labeling.
+
+.. seealso:: :py:func:`mapBoundaryGeometry`
+
+.. seealso:: :py:func:`setExtent`
+%End
+
+    void setExtent( const QgsRectangle &extent );
+%Docstring
+Sets the map ``extent`` defining the limits for labeling.
+
+.. seealso:: :py:func:`setMapBoundaryGeometry`
+
+.. seealso:: :py:func:`extent`
+%End
+
+    QgsGeometry mapBoundaryGeometry() const;
+%Docstring
+Returns the map label boundary geometry, which defines the limits within which labels may be placed
+in the map.
+
+The map boundary geometry specifies the actual geometry of the map
+boundary, which will be used to detect whether a label is visible (or partially visible) in
+the rendered map. This may differ from :py:func:`~QgsLabelingEngineContext.extent` in the case of rotated or non-rectangular
+maps.
+
+.. seealso:: :py:func:`setMapBoundaryGeometry`
+
+.. seealso:: :py:func:`extent`
+%End
+
+    void setMapBoundaryGeometry( const QgsGeometry &geometry );
+%Docstring
+Sets the map label boundary ``geometry``, which defines the limits within which labels may be placed
+in the map.
+
+The map boundary geometry specifies the actual geometry of the map
+boundary, which will be used to detect whether a label is visible (or partially visible) in
+the rendered map. This may differ from :py:func:`~QgsLabelingEngineContext.extent` in the case of rotated or non-rectangular
+maps.
+
+.. seealso:: :py:func:`setExtent`
+
+.. seealso:: :py:func:`mapBoundaryGeometry`
+%End
+
+  private:
+    QgsLabelingEngineContext( const QgsLabelingEngineContext &other );
+};
+
+class QgsAbstractLabelingEngineRule
+{
+%Docstring(signature="appended")
+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::
+
+   :py:class:`QgsAbstractLabelingEngineRule` cannot be subclassed in Python. Use one of the existing
+   implementations of this class instead.
+
+.. versionadded:: 3.40
+%End
+
+%TypeHeaderCode
+#include "qgslabelingenginerule.h"
+%End
+%ConvertToSubClassCode
+    if ( sipCpp->id() == "minimumDistanceLabelToFeature" )
+    {
+      sipType = sipType_QgsLabelingEngineRuleMinimumDistanceLabelToFeature;
+    }
+    else if ( sipCpp->id() == "minimumDistanceLabelToLabel" )
+    {
+      sipType = sipType_QgsLabelingEngineRuleMinimumDistanceLabelToLabel;
+    }
+    else if ( sipCpp->id() == "maximumDistanceLabelToFeature" )
+    {
+      sipType = sipType_QgsLabelingEngineRuleMaximumDistanceLabelToFeature;
+    }
+    else if ( sipCpp->id() == "avoidLabelOverlapWithFeature" )
+    {
+      sipType = sipType_QgsLabelingEngineRuleAvoidLabelOverlapWithFeature;
+    }
+    else
+    {
+      sipType = 0;
+    }
+%End
+  public:
+
+    virtual ~QgsAbstractLabelingEngineRule();
+
+    virtual QgsAbstractLabelingEngineRule *clone() const = 0 /Factory/;
+%Docstring
+Creates a clone of this rule.
+
+The caller takes ownership of the returned object.
+%End
+
+    virtual QString id() const = 0;
+%Docstring
+Returns a string uniquely identifying the rule subclass.
+%End
+
+    virtual bool prepare( QgsRenderContext &context ) = 0;
+%Docstring
+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.
+%End
+
+    virtual void writeXml( QDomDocument &doc, QDomElement &element, const QgsReadWriteContext &context ) const = 0;
+%Docstring
+Writes the rule properties to an XML ``element``.
+
+.. seealso:: :py:func:`readXml`
+%End
+
+    virtual void readXml( const QDomElement &element, const QgsReadWriteContext &context ) = 0;
+%Docstring
+Reads the rule properties from an XML ``element``.
+
+.. seealso:: :py:func:`resolveReferences`
+
+.. seealso:: :py:func:`writeXml`
+%End
+
+    virtual void resolveReferences( const QgsProject *project );
+%Docstring
+Resolves reference to layers from stored layer ID.
+
+Should be called following a call :py:func:`~QgsAbstractLabelingEngineRule.readXml`.
+%End
+
+
+
+
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/labeling/rules/qgslabelingenginerule.h                      *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/