Virtual point clouds overview in 2D

[Withalion]

Description

This PR changes the default behaviour of VPC rendering. We switch from rendering extents when zoomed out to rendering overview when it's present. This change adds seamless transition between overview into specific point clouds. Furthermore the user is able to switch between just extents, just overview and extents rendered over overview, by using combo box in layer styling side panel.

Screencast_20241212_142233.mp4

The label settings were also moved together with zoom out behaviour settings into new Virtual point cloud options QgsCollapsibleGroupBox. Which is visible only when dealing with virtual point clouds styling.

Note: When I dealt with setting the default Qgis::PointCloudZoomOutBehavior for layer renderer I noticed that the renderer is actually created multiple times!

• First time the renderer gets created in QgsPointCloudLayer::setDataSourcePrivate, which is called by constructor
  

  QGIS/src/core/pointcloud/qgspointcloudlayer.cpp

  Lines 467 to 487 in fb501d5

  	if ( loadDefaultStyleFlag && isSpatial() && mDataProvider->capabilities() & QgsPointCloudDataProvider::CreateRenderer )
  	{
  	// first try to create a renderer directly from the data provider
  	std::unique_ptr< QgsPointCloudRenderer > defaultRenderer( mDataProvider->createRenderer() );
  	if ( defaultRenderer )
  	{
  	defaultLoadedFlag = true;
  	setRenderer( defaultRenderer.release() );
  	}
  	}
  	if ( !defaultLoadedFlag && loadDefaultStyleFlag )
  	{
  	loadDefaultStyle( defaultLoadedFlag );
  	}
  	if ( !defaultLoadedFlag )
  	{
  	// all else failed, create default renderer
  	setRenderer( QgsPointCloudRendererRegistry::defaultRenderer( this ) );
  	}

• Second time the renderer is created by QgsAppLayerHandling::postProcessAddedLayer
  

  QGIS/src/app/layers/qgsapplayerhandling.cpp

  Line 187 in fb501d5

  layer->loadDefaultStyle( ok );

Note 2: The layer has to be readded into the project for qgis to apply the default behaviour.

Funded by: Klimadatastyrelsen

[github-actions]

🪟 Windows builds

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Debug symbols for this build are available here.
(Built from commit 08380e2)

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit 08380e2)

[uclaros]

Nice!
I have an objection on the need for those averageSubIndexWidth and averageSubIndexHeight methods, though.

[nyalldawson]

This will need some unit tests added too 👍

[qgis-bot]

@Withalion

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[qgis-bot]

@Withalion
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
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[wonder-sk]

Looks great! 👏

[qgis-bot]

@Withalion
A documentation ticket has been opened at qgis/QGIS-Documentation#9532
It is your responsibility to visit this ticket and add as much detail as possible for the documentation team to correctly document this change.
Thank you!