QgsRuleBasedLabelProvider class

Base classes

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

class QgsDxfRuleBasedLabelProvider: Implements a derived label provider for rule based labels internally used for DXF export.

auto createProvider(QgsVectorLayer* layer, const QString& providerId, bool withFeatureLoop, const QgsPalLayerSettings* settings) -> QgsVectorLayerLabelProvider* virtual: create a label provider
auto prepare(const QgsRenderContext& context, QSet<QString>& attributeNames) -> bool override: Prepare for registration of features.
void registerFeature(QgsFeature& feature, QgsRenderContext& context, const QgsGeometry& obstacleGeometry = QgsGeometry()) override: Register a feature for labeling as one or more QgsLabelFeature objects stored into mLabels.
auto subProviders() -> QList<QgsAbstractLabelProvider*> override: Returns subproviders.

std::unique_ptr<QgsRuleBasedLabeling> mRules: owned copy
QgsRuleBasedLabeling::RuleToProviderMap mSubProviders: label providers are owned by labeling engine

Prepare for registration of features.

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

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

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.