Class: QgsMapRendererCache

class qgis.core.QgsMapRendererCache

Bases: PyQt5.QtCore.QObject

This class is responsible for keeping cache of rendered images resulting from a map rendering job.

Once a job has a rendered image stored in the cache (using setCacheImage(…)), the cache listens to repaintRequested() signals from dependent layers. If triggered, the cache removes the rendered image (and disconnects from the layers).

The class is thread-safe (multiple classes can access the same instance safely).

Methods

cacheImage

Returns the cached image for the specified cacheKey.

childEvent

clear

Invalidates the cache contents, clearing all cached images.

clearCacheImage

Removes an image from the cache with matching cacheKey.

connectNotify

customEvent

dependentLayers

Returns a list of map layers on which an image in the cache depends.

disconnectNotify

hasCacheImage

Returns True if the cache contains an image with the specified cacheKey.

init

Initialize cache: set new parameters and clears the cache if any parameters have changed since last initialization.

isSignalConnected

receivers

sender

senderSignalIndex

setCacheImage

Set the cached image for a particular cacheKey.

timerEvent

cacheImage(self, cacheKey: str) → QImage

Returns the cached image for the specified cacheKey. The cacheKey usually matches the QgsMapLayer.id() which the image is a render of. Returns a null image if it is not cached.

See also

setCacheImage()

See also

hasCacheImage()

Parameters

cacheKey (str) –

Return type

QImage

childEvent()
clear(self)

Invalidates the cache contents, clearing all cached images.

clearCacheImage(self, cacheKey: str)

Removes an image from the cache with matching cacheKey.

See also

clear()

Parameters

cacheKey (str) –

connectNotify()
customEvent()
dependentLayers(self, cacheKey: str) → List[QgsMapLayer]

Returns a list of map layers on which an image in the cache depends.

New in version 3.0.

Parameters

cacheKey (str) –

Return type

List[QgsMapLayer]

disconnectNotify()
hasCacheImage(self, cacheKey: str) → bool

Returns True if the cache contains an image with the specified cacheKey.

See also

cacheImage()

New in version 3.0.

Parameters

cacheKey (str) –

Return type

bool

init(self, extent: QgsRectangle, scale: float) → bool

Initialize cache: set new parameters and clears the cache if any parameters have changed since last initialization.

Return type

bool

Returns

flag whether the parameters are the same as last time

Parameters
isSignalConnected()
receivers()
sender()
senderSignalIndex()
setCacheImage(self, cacheKey: str, image: QImage, dependentLayers: Iterable[QgsMapLayer] = [])

Set the cached image for a particular cacheKey. The cacheKey usually matches the QgsMapLayer.id() which the image is a render of. A list of dependentLayers should be passed containing all layer on which this cache image is dependent. If any of these layers triggers a repaint then the cache image will be cleared.

See also

cacheImage()

Parameters
  • cacheKey (str) –

  • image (QImage) –

  • dependentLayers (Iterable[QgsMapLayer] = []) –

timerEvent()