[advanced digitizing] Implement visual construction guides

[nirvn]

Description

This PR adds visual construction guides to the advanced digitizing dock widget which builds on top of our preexisting CAD construction mode.

UI wise, the functionality is exposed through a set of actions within a new drop-down menu attached to the construction activation toolbar button:

When recording construction guides, QGIS will render all construction steps taken as dashed lines. Those lines will remain visible as long as advanced digitizing is enabled. The guides are snap-able, allowing for construction steps to begin mid-way into a previous set of steps too.

In action:

vokoscreenNG-2024-05-28_11-26-37.mp4

The construction guides are stored in a vector layer, which is exposed through the advanced digitizing dock widget, allowing for further customization of those guides via e.g. python plugins.

[github-actions]

🪟 Windows builds ready!

Windows builds of this PR are available for testing here. Debug symbols for this build are available here.

(Built from commit 35784b2)

[lbartoletti]

Very interesting feature!

Some questions:

• Is the layer available in the layertree ? (Personnaly, I don't want to see it in)
• Is it possible to save the construction layer ?
• What is the projection of the layer ? Same as the project one ?
• What are the snapping options for this layer ?

Thanks!

[nirvn]

@lbartoletti , glad this functionality is peaking your interest :)

Here are As to your Qs:

• The layer is not available in the layer tree; it is however publicly exposed through the QgsAdvancedDigitizingDockerWidget, which means it can be accessed via python (console, plugins, etc.) via iface.cadDockWidget().constructionGuidesLayer(). This makes it possible to prototype further enhancements through python (either as proof of concept prior to implementation in src/gui, or simply as a cool plugin :).
• The initial implementation here does not expose a 'save guides to file', but it can easily be implemented in the future (or right away in python scripting via QgsVectorFileWriter). The PR aims at laying a foundation upon which we can build on.
• That is correct, the layer that holds the guide adopts the project CRS. If that is changed during the course of a project session, the guides will be reprojected to match the changed project CRS.
• The layer will adopt the poject's snapping configuration set in the snapping toolbar.

[nirvn]

@nyalldawson , thanks for the review, your comments were addressed. A couple of tests were also added to test guide recording and snapping.

[nyalldawson]

Just one small tweak

[nyalldawson]

Suggested change

	QgsFeatureIterator it = constructionGuidesLayer->getFeatures( mMapCanvas->mapSettings().visibleExtent() );
	QgsFeatureIterator it = constructionGuidesLayer->getFeatures( QgsFeatureRequest().setNoAttributes().setFilterRect( mMapCanvas->mapSettings().visibleExtent() ) );

[uclaros]

In the video, at 0:34 it appears like you need to click on Show construction guides twice for the option to get unchecked. Is that the case?

[qgis-bot]

@nirvn

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[qgis-bot]

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

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[qgis-bot]

@nirvn
A documentation ticket has been opened at qgis/QGIS-Documentation#9274
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