Class: QgsMapLayerRenderer¶

Base class for utility classes that encapsulate information necessary for rendering of map layers.

The rendering is typically done in a background thread, so it is necessary to keep all structures required for rendering away from the original map layer because it may change any time.

Because the data needs to be copied (to avoid the need for locking), it is highly desirable to use copy-on-write where possible. This way, the overhead of copying (both memory and CPU) will be kept low. Qt containers and various Qt classes use implicit sharing.

The scenario will be:

renderer job (doing preparation in the GUI thread) calls QgsMapLayer.createMapRenderer() and gets instance of this class. The instance is initialized at that point and should not need additional calls to QgsVectorLayer.
renderer job (still in GUI thread) stores the renderer for later use.
renderer job (in worker thread) calls QgsMapLayerRenderer.render()
renderer job (again in GUI thread) will check errors() and report them

Note

This is an abstract class, with methods which must be implemented by a subclass.

The following methods must be implemented: render()

Abstract Methods

render

Do the rendering (based on data stored in the class).

Methods

`appendRenderedItemDetails`	Appends the details of a rendered item to the renderer.
`errors`	Returns list of errors (problems) that happened during the rendering
`isReadyToCompose`	Returns whether the renderer has already drawn (at least partially) some data
`layerId`	Gets access to the ID of the layer rendered by this class
`renderContext`	Returns the render context associated with the renderer.
`takeRenderedItemDetails`	Takes the list of rendered item details from the renderer.

Virtual Methods

In PyQGIS, only methods marked as virtual can be safely overridden in a Python subclass of QgsMapLayerRenderer. See the FAQ for more details.

`feedback`	Access to feedback object of the layer renderer (may be `None`)
`flags`	Returns flags which control how the map layer rendering behaves.
`forceRasterRender`	Returns `True` if the renderer must be rendered to a raster paint device (e.g. QImage).

class qgis.core.QgsMapLayerRenderer[source]¶

Bases: object

__init__(layerID: str | None, context: QgsRenderContext | None = None)

Constructor for QgsMapLayerRenderer, with the associated layerID and render context.

Parameters:

layerID (Optional[str])
context (Optional[QgsRenderContext] = None)

__init__(a0: QgsMapLayerRenderer)

Parameters:: a0 (QgsMapLayerRenderer)

appendRenderedItemDetails(self, details: QgsRenderedItemDetails | None)[source]¶

Appends the details of a rendered item to the renderer.

Rendered item details can be retrieved by calling takeRenderedItemDetails().

Ownership of details is transferred to the renderer.