Class: QgsMapLayerRenderer

class qgis.core.QgsMapLayerRenderer

Bases: sip.wrapper

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

New in version 2.4.

QgsMapLayerRenderer(layerID: str, context: QgsRenderContext = None) Constructor for QgsMapLayerRenderer, with the associated layerID and render context.

QgsMapLayerRenderer(QgsMapLayerRenderer)

Methods

errors

Returns list of errors (problems) that happened during the rendering

feedback

Access to feedback object of the layer renderer (may be None)

forceRasterRender

Returns True if the renderer must be rendered to a raster paint device (e.g.

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

render

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

renderContext

Returns the render context associated with the renderer.

errors(self)List[str]

Returns list of errors (problems) that happened during the rendering

Return type

List[str]

feedback(self)QgsFeedback

Access to feedback object of the layer renderer (may be None)

New in version 3.0.

Return type

QgsFeedback

forceRasterRender(self)bool

Returns True if the renderer must be rendered to a raster paint device (e.g. QImage).

Some layer settings require layers to be effectively “flattened” while rendering maps, which is achieved by first rendering the layer onto a raster paint device and then compositing the resultant image onto the final map render.

E.g. if a layer contains features with transparency or alternative blending modes, and the effects of these opacity or blending modes should be restricted to only affect other features within the SAME layer, then a flattened raster based render is required.

Subclasses should return True whenever their corresponding layer settings require the layer to always be rendered using a raster paint device.

New in version 3.18.

Return type

bool

isReadyToCompose(self)bool

Returns whether the renderer has already drawn (at least partially) some data

New in version 3.18.

Return type

bool

layerId(self)str

Gets access to the ID of the layer rendered by this class

Return type

str

render(self)bool

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

Returns True if the layer was completely rendered successfully (i.e. the render was not canceled early).

Return type

bool

renderContext(self)QgsRenderContext

Returns the render context associated with the renderer.

New in version 3.10.

Return type

QgsRenderContext