QgsVectorLayerDiagramProvider class

The QgsVectorLayerDiagramProvider class implements support for diagrams within the labeling engine.

Parameters for the diagrams are taken from the layer settings.

Base classes

class QgsAbstractLabelProvider: The QgsAbstractLabelProvider class is an interface class.

QgsVectorLayerDiagramProvider(QgsVectorLayer* layer, bool ownFeatureLoop = true) explicit: Convenience constructor to initialize the provider from given vector layer.
~QgsVectorLayerDiagramProvider() override: Clean up.

void drawLabel(QgsRenderContext& context, pal::LabelPosition* label) const override: draw this label at the position determined by the labeling engine
auto labelFeatures(QgsRenderContext& context) -> QList<QgsLabelFeature*> override: Returns list of label features (they are owned by the provider and thus deleted on its destruction)
auto prepare(const QgsRenderContext& context, QSet<QString>& attributeNames) -> bool virtual: Prepare for registration of features.
void registerFeature(QgsFeature& feature, QgsRenderContext& context, const QgsGeometry& obstacleGeometry = QgsGeometry()) virtual: Register a feature for labeling as one or more QgsLabelFeature objects stored into mFeatures.

void init(): initialization method - called from constructors
auto registerDiagram(QgsFeature& feat, QgsRenderContext& context, const QgsGeometry& obstacleGeometry = QgsGeometry()) -> QgsLabelFeature*: helper method to register one diagram feature

QgsDiagramRenderer* mDiagRenderer: Diagram renderer instance (owned by mSettings)
QList<QgsLabelFeature*> mFeatures: List of generated label features (owned by the provider)
QgsFields mFields: Layer's fields.
QgsCoordinateReferenceSystem mLayerCrs: Layer's CRS.
bool mOwnsSource: Whether layer's feature source is owned.
QgsDiagramLayerSettings mSettings: Diagram layer settings.
QgsAbstractFeatureSource* mSource: Layer's feature source.

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 for diagram
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. Ownership of obstacleGeometry is transferred.