QgsMapLayerRenderer Class Reference

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

#include <qgsmaplayerrenderer.h>

Inheritance diagram for QgsMapLayerRenderer:

Public Member Functions
	QgsMapLayerRenderer (const QString &layerID, QgsRenderContext *context=nullptr)
	Constructor for QgsMapLayerRenderer, with the associated layerID and render context. More...
virtual	~QgsMapLayerRenderer ()
QStringList	errors () const
	Returns list of errors (problems) that happened during the rendering. More...
virtual QgsFeedback *	feedback () const
	Access to feedback object of the layer renderer (may be nullptr) More...
virtual bool	forceRasterRender () const
	Returns true if the renderer must be rendered to a raster paint device (e.g. More...
bool	isReadyToCompose () const
	Returns whether the renderer has already drawn (at least partially) some data. More...
QString	layerId () const
	Gets access to the ID of the layer rendered by this class. More...
virtual bool	render ()=0
	Do the rendering (based on data stored in the class). More...
QgsRenderContext *	renderContext ()
	Returns the render context associated with the renderer. More...
const QgsRenderContext *	renderContext () const
	Returns the render context associated with the renderer. More...
virtual void	setLayerRenderingTimeHint (int time)
	Sets approximate render time (in ms) for the layer to render. More...
QList< QgsRenderedItemDetails * >	takeRenderedItemDetails ()
	Takes the list of rendered item details from the renderer. More...

Protected Member Functions
void	appendRenderedItemDetails (QgsRenderedItemDetails *details)
	Appends the details of a rendered item to the renderer. More...

Protected Attributes
QStringList	mErrors
QString	mLayerID
bool	mReadyToCompose = true
	The flag must be set to false in renderer's constructor if wants to use the smarter map redraws functionality https://github.com/qgis/QGIS-Enhancement-Proposals/issues/181. More...

Static Protected Attributes
static constexpr int	MAX_TIME_TO_USE_CACHED_PREVIEW_IMAGE = 3000
	Maximum time (in ms) to allow display of a previously cached preview image while rendering layers, before switching to a progressive rendering display. More...

Detailed Description

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

Since

QGIS 2.4

Definition at line 54 of file qgsmaplayerrenderer.h.

Constructor & Destructor Documentation

QgsMapLayerRenderer()

QgsMapLayerRenderer::QgsMapLayerRenderer ( const QString &  layerID, QgsRenderContext *  context = nullptr  )

inline

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

Definition at line 61 of file qgsmaplayerrenderer.h.

~QgsMapLayerRenderer()

QgsMapLayerRenderer::~QgsMapLayerRenderer ( )

virtualdefault

Member Function Documentation

appendRenderedItemDetails()

void QgsMapLayerRenderer::appendRenderedItemDetails ( QgsRenderedItemDetails *  details )

protected

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.

See also

takeRenderedItemDetails()

Since

QGIS 3.22

Definition at line 27 of file qgsmaplayerrenderer.cpp.

errors()

QStringList QgsMapLayerRenderer::errors ( ) const

inline

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

Definition at line 101 of file qgsmaplayerrenderer.h.

feedback()

virtual QgsFeedback * QgsMapLayerRenderer::feedback ( ) const

inlinevirtual

Access to feedback object of the layer renderer (may be nullptr)

Since

QGIS 3.0

Reimplemented in QgsAnnotationLayerRenderer, QgsMeshLayerRenderer, QgsPointCloudLayerRenderer, QgsGroupLayerRenderer, QgsRasterLayerRenderer, QgsVectorLayerRenderer, and QgsVectorTileLayerRenderer.

Definition at line 98 of file qgsmaplayerrenderer.h.

forceRasterRender()

virtual bool QgsMapLayerRenderer::forceRasterRender ( ) const

inlinevirtual

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.

Since

QGIS 3.18

Reimplemented in QgsAnnotationLayerRenderer, QgsMeshLayerRenderer, QgsPointCloudLayerRenderer, QgsGroupLayerRenderer, QgsRasterLayerRenderer, QgsVectorLayerRenderer, and QgsVectorTileLayerRenderer.

Definition at line 92 of file qgsmaplayerrenderer.h.

isReadyToCompose()

bool QgsMapLayerRenderer::isReadyToCompose ( ) const

inline

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

Since

QGIS 3.18

Definition at line 127 of file qgsmaplayerrenderer.h.

layerId()

QString QgsMapLayerRenderer::layerId ( ) const

inline

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

Definition at line 104 of file qgsmaplayerrenderer.h.

render()

virtual bool QgsMapLayerRenderer::render ( )

pure virtual

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).

Implemented in QgsAnnotationLayerRenderer, QgsMeshLayerRenderer, QgsPointCloudLayerRenderer, QgsGroupLayerRenderer, QgsRasterLayerRenderer, QgsVectorLayerRenderer, and QgsVectorTileLayerRenderer.

renderContext() [1/2]

QgsRenderContext * QgsMapLayerRenderer::renderContext ( )

inline

Returns the render context associated with the renderer.

Since

QGIS 3.10

Definition at line 111 of file qgsmaplayerrenderer.h.

renderContext() [2/2]

const QgsRenderContext * QgsMapLayerRenderer::renderContext ( ) const

inline

Returns the render context associated with the renderer.

Note

Not available in Python bindings

Since

QGIS 3.18

Definition at line 119 of file qgsmaplayerrenderer.h.

setLayerRenderingTimeHint()

virtual void QgsMapLayerRenderer::setLayerRenderingTimeHint ( int  time )

inlinevirtual

Sets approximate render time (in ms) for the layer to render.

This can be used to specifies a hint at the expected render times for the layer, so that the individual layer renderer subclasses can apply heuristics and determine appropriate update intervals during the render operation.

Note

Not available in Python bindings.

Since

QGIS 3.18

Reimplemented in QgsPointCloudLayerRenderer, and QgsVectorLayerRenderer.

Definition at line 139 of file qgsmaplayerrenderer.h.

takeRenderedItemDetails()

QList< QgsRenderedItemDetails * > QgsMapLayerRenderer::takeRenderedItemDetails

(

)

Takes the list of rendered item details from the renderer.

Ownership of items is transferred to the caller.

See also

appendRenderedItemDetails()

Since

QGIS 3.22

Definition at line 22 of file qgsmaplayerrenderer.cpp.

Member Data Documentation

MAX_TIME_TO_USE_CACHED_PREVIEW_IMAGE

constexpr int QgsMapLayerRenderer::MAX_TIME_TO_USE_CACHED_PREVIEW_IMAGE = 3000

staticconstexprprotected

Maximum time (in ms) to allow display of a previously cached preview image while rendering layers, before switching to a progressive rendering display.

Note

Not available in Python bindings

Since

QGIS 3.18

Definition at line 181 of file qgsmaplayerrenderer.h.

mErrors

QStringList QgsMapLayerRenderer::mErrors

protected

Definition at line 152 of file qgsmaplayerrenderer.h.

mLayerID

QString QgsMapLayerRenderer::mLayerID

protected

Definition at line 153 of file qgsmaplayerrenderer.h.

mReadyToCompose

bool QgsMapLayerRenderer::mReadyToCompose = true

protected

The flag must be set to false in renderer's constructor if wants to use the smarter map redraws functionality https://github.com/qgis/QGIS-Enhancement-Proposals/issues/181.

The flag must be set to true by renderer when the data is fetched and the renderer actually started to update the destination image.

When the flag is set to false, the image from QgsMapRendererCache is used instead to avoid flickering.

Since

QGIS 3.18

Definition at line 171 of file qgsmaplayerrenderer.h.

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The documentation for this class was generated from the following files:

• /build/qgis-3.28.0+99sid/src/core/qgsmaplayerrenderer.h
• /build/qgis-3.28.0+99sid/src/core/qgsmaplayerrenderer.cpp