Multi-Select with Ctrl + Mouse Click

[Sebanisu]

📋 Summary

Currently, clicking on a tile selects all tile indexes under the mouse at that position (x, y). A single mouse_down is recorded, and tiles are transformed via ImGuizmo by tracking the difference between mouse_down and mouse_pos.

We want to extend this to support multi-selection using Ctrl + Mouse Click, allowing users to select and manipulate multiple tiles at once.

Related to: #113

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Current Behavior

• Mouse click at (x, y) loads all tile indexes at that location into a selection vector.
• A single mouse_down is stored.
• ImGuizmo is anchored at mouse_down.
• Moving the mouse updates mouse_pos, which is used to compute the delta transform for selected tiles.
• The tiles are live-updated by the delta between mouse_down and mouse_pos.
• After each move, mouse_down is updated to the current mouse_pos.

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Proposed Behavior

• Ctrl + Mouse Click:
  • Appends the tile indexes at the clicked position to the selection vector.
  • Deduplicates and sorts the list to avoid overlapping transformations.
  • Tracks a list of mouse_down points corresponding to each Ctrl-clicked tile cluster.
  • Computes the centroid of all mouse_down points.
• On Transform (via ImGuizmo):
  • Anchor the gizmo at the centroid.
  • On drag, compute delta between mouse_pos and the previous centroid.
  • Move all selected tiles by this delta.
  • Update centroid.
  • Shift all stored mouse_down points by the same delta.
    • This keeps them aligned with the tiles in case of additional Ctrl + clicks (i.e. adding to selection after moving).

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🔧 Implementation Notes

• Add a multi_selection mode enabled by checking Ctrl key state during mouse click.
• Use a std::vector<glm::uvec2> (or equivalent) to store multiple mouse_down points.
• Selection vector stores tile indexes, sorted and deduplicated.
• Add helper functions to:
  • Compute centroid of a list of points.
  • Apply transformation delta to all selected tiles.
  • Shift stored mouse_down points by delta after each move.
• UI feedback: ImGuizmo appears at the centroid of selected tiles when multiple are selected.

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Testing Considerations

• Select multiple tiles by Ctrl + clicking at various positions.
• Ensure ImGuizmo appears at the centroid and moves all selected tiles consistently.
• Check that dragging continues to update the centroid and tile positions correctly.
• Verify that stored mouse_down points are updated so that adding to the selection still works as expected after moving tiles.

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Future Improvements

• Support deselection via Ctrl + click on already-selected tiles.