Class: QgsMapLayerRenderer¶
- class qgis.core.QgsMapLayerRenderer(layerID: str, context: QgsRenderContext = None)¶
Bases:
sip.wrapper
Constructor for
QgsMapLayerRenderer
, with the associatedlayerID
and rendercontext
.QgsMapLayerRenderer(
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 toQgsVectorLayer
.
# 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 checkerrors()
and report themMethods
Returns list of errors (problems) that happened during the rendering
Access to feedback object of the layer renderer (may be
None
)Returns
True
if the renderer must be rendered to a raster paint device (e.g.Returns whether the renderer has already drawn (at least partially) some data
Gets access to the ID of the layer rendered by this class
Do the rendering (based on data stored in the class).
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
- 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