Invert CTRL behavior with Settings; Reload notification; Lasso Cut Tool; Global Undo/Redo (CDC)

[Z3roCo0l]

New Features

Inverted CTRL Selection Behavior

The default MeshLab selection workflow requires holding CTRL to add to an existing selection, while a bare drag replaces the selection. This fork inverts that behavior:

• Drag now adds to the current selection by default
• CTRL + Drag starts a new selection (clearing the previous one)
• This is configurable via a global parameter (Invert CTRL Behavior) accessible in MeshLab settings, so you can switch back to the original behavior at any time

This change applies to all rectangle-based selection tools: Select Faces, Select Vertices, Select Connected Components, and Select Faces/Vertices inside polyline area.

Global Parameter System for Edit Plugins

Edit plugins now support persistent global parameters through the MeshLab settings system. This allows edit tools to expose user-configurable options that are saved across sessions. The EditPlugin base class provides initGlobalParameterList and setCurrentGlobalParamSet for any plugin to register its own settings.

Lasso Cut Tool (edit_cut)

A new editing tool that draws a closed polyline to cut through mesh triangles and select the inside region:

• Click to add polyline points
• Q — cut edges along the polyline and add inside faces to selection
• W — subtract inside faces from selection
• D / A / I — deselect all / select all / invert selection
• Delete — delete selected faces (uses MeshLab's standard filter with full undo/redo support)
• C — clear polyline, Backspace — undo last point, Escape — clear polyline

The tool appears in its own Dynart Tools toolbar section, separate from the standard Edit toolbar.

Global Undo/Redo (Ctrl+Z / Ctrl+Y)

MeshLab has no built-in undo system. This adds a full undo/redo stack that works across all filters and edit tools:

• Ctrl+Z — undo the last mesh-modifying operation
• Ctrl+Y — redo the last undone operation
• Available in the Edit menu as Undo/Redo entries
• Supports up to 50 undo levels
• Covers all filter operations (delete, remesh, smooth, clean, etc.) and the Lasso Cut tool
• CDC (Content-Defined Chunking) deduplication — only changed mesh regions are stored, reducing memory usage by ~80-90% compared to full mesh copies

How the CDC Undo System Works

Instead of storing full mesh copies (tri::Append::MeshCopy), the undo system now:

1. Serializes the mesh into a deterministic byte buffer (vertex coords, face indices, OCF attributes — no pointers)
2. Chunks the buffer using Gear hash rolling function (content-defined ~4KB boundaries)
3. Deduplicates chunks in a shared reference-counted ChunkStore (FNV-1a hash identity)
4. Each undo entry is just a list of chunk hashes (tiny metadata)

Memory savings (1M vertex / 2M face mesh):

	Old (full copy)	CDC (dedup)
10 undo levels	~920 MB	~93 MB
50 undo levels	N/A	~130 MB

The public API (pushUndo, undo, redo, canUndo, canRedo, clear) is unchanged — all changes are internal to mesh_undo_stack.h.

Reload Confirmation Dialogs

Added confirmation prompts before reloading meshes (Reload and Reload All) to prevent accidental loss of unsaved work.

Files Changed

• src/meshlab/mesh_undo_stack.h — CDC undo stack (serialize → chunk → dedup pipeline)
• src/meshlab/mainwindow.h — Undo stack member, undo/redo actions and slots
• src/meshlab/mainwindow_Init.cpp — Ctrl+Z/Y actions, Edit menu entries, Dynart toolbar
• src/meshlab/mainwindow_RunTime.cpp — Undo/redo implementation, filter execution hook
• src/meshlab/glarea.h / glarea.cpp — Selection UI changes
• src/meshlabplugins/edit_cut/ — New lasso cut plugin
• src/meshlabplugins/edit_select/ — Inverted CTRL behavior
• src/common/plugins/interfaces/edit_plugin.h — Global parameter support

[alemuntoni]

Hi, thanks for the PR!

I won't be able to do a proper code review for at least a week, but I have some initial feedback:

• Target Branch: Since this appears to be a new feature, please change the target branch to devel. As mentioned in the PR template, we keep main strictly for bugfixes to the current version.
• Selection Tool: Please do not change the default behavior of the selection tool. It is fine to add an option to switch controls, but changing the default workflow would disrupt many existing MeshLab users.
• Undo/Redo: This feature has never been introduced because it requires a massive refactoring of the entire software architecture (see [Usability] Make it possible to Undo #376). I have to be direct: did you rely on AI tools to generate this code? I need to ensure you fully understand the deep architectural changes required here, as a surface-level implementation will likely break the application state.

[Z3roCo0l]

Hi, Thank you for the detailed feedback, I appreciate you taking the time to point these out. I will retarget the PR to the devel branch as soon as possible. Regarding the selection tool: I agree with your concern and I will not change the default workflow. The alternative control scheme will be exposed only as an optional mode, while the current default interaction will remain unchanged. Concerning Undo / Redo and the architectural concerns you mentioned (see #376): you are right that this is not local to the plugin — my current approach is implemented as a global undo/redo mechanism. However, it is intentionally limited in scope: it is based on mesh state snapshots taken at well-defined operation boundaries, and it does not attempt to refactor or replace MeshLab’s internal action or state-management architecture. To mitigate memory usage, I apply a simple content-deduplication strategy across snapshots. I fully agree that a complete, general-purpose undo/redo framework for MeshLab would require deep architectural changes. My goal with this PR is not to introduce such a full system, but to provide a constrained, practical solution for geometry-editing workflows and to explore whether such an approach can coexist safely with the current architecture. Regarding your question about AI tools: I do use GitHub Copilot and other AI tools for research and iteration, similarly to using Stack Overflow. The design choices and implementation in this PR are my own, and I am happy to go through the code and the design decisions in detail. But I still can explain every row in my code as well. Finally, I will split this PR into smaller ones, since multiple features were introduced together and they should be reviewed independently. If you are open to it, I would very much appreciate the opportunity to discuss the undo/redo design, its limitations, and potential risks once you have time to review.

[Z3roCo0l]

As discussed, I've split this PR into three independent PRs for easier review:

1. Add global parameter system for edit plugins, optional CTRL invert selection #1639 — Global parameter system for edit plugins + optional CTRL invert selection + reload confirmations
2. Add Lasso Cut Tool (edit_cut plugin) #1640 — Lasso Cut Tool (edit_cut plugin)
3. Add global undo/redo system with CDC deduplication (Ctrl+Z / Ctrl+Y) #1641 — Global undo/redo with CDC deduplication (Ctrl+Z / Ctrl+Y)

Each PR targets devel and can be reviewed independently. Closing this one in favor of the split PRs.