QgsVectorLayerLabelProvider class
The QgsVectorLayerLabelProvider class implements a label provider for vector layers.
Contents
Parameters for the labeling are taken from the layer's custom properties or from the given settings.
Base classes
- class QgsAbstractLabelProvider
- The QgsAbstractLabelProvider class is an interface class.
Derived classes
- class QgsDxfLabelProvider
- Implements a derived label provider internally used for DXF export.
- class QgsRuleBasedLabelProvider
Public static functions
- static auto getPointObstacleGeometry(QgsFeature& fet, QgsRenderContext& context, const QgsSymbolList& symbols) -> QgsGeometry
- Returns the geometry for a point feature which should be used as an obstacle for labels.
Constructors, destructors, conversion operators
- 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.
Public functions
-
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 mLabels.
Protected functions
-
void drawLabelPrivate(pal::
LabelPosition* label, QgsRenderContext& context, QgsPalLayerSettings& tmpLyr, QgsTextRenderer:: TextPart drawType, double dpiRatio = 1.0) const - Internal label drawing method.
- void init()
- initialization method - called from constructors
Protected variables
- QgsCoordinateReferenceSystem mCrs
- Layer's CRS.
- QgsFields mFields
- Layer's fields.
- QList<QgsLabelFeature*> mLabels
- List of generated.
-
QgsWkbTypes::
GeometryType mLayerGeometryType - Geometry type of layer.
- bool mOwnsSource
- Whether layer's feature source is owned.
- QgsPalLayerSettings mSettings
- Layer's labeling configuration.
- QgsAbstractFeatureSource* mSource
- Layer's feature source.
Function documentation
static QgsGeometry QgsVectorLayerLabelProvider::
Returns the geometry for a point feature which should be used as an obstacle for labels.
| Parameters | |
|---|---|
| fet | point feature |
| context | render context |
| symbols | symbols rendered for point feature |
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.
bool QgsVectorLayerLabelProvider::
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)
void QgsVectorLayerLabelProvider::
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. |