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Selection System

The selection system provides tools for selecting and managing units through UI interactions. It supports both single-click selection and drag-selection for multiple units.

Overview​

The selection system enables players to select units by clicking on them or dragging a selection box. The system is split between Blueprint logic (for UI interaction) and C++ logic (for efficient entity querying and selection management).

How Selection Works​

Blueprint Layer​

The start of the unit selection logic flow is inside the blueprint AC_SelectionSystem_Basic.

On Click Selection:

  • The system gets the mouse position on the viewport
  • It saves both the mouse start position and the mouse end position
  • For single clicks, it selects the unit at that location

Drag Selection:

  • If it's a drag and drop selection, the system creates a quad corner vector list
  • These are 4 vectors which build a rectangle on the map
  • With these 4 vectors, the system can check which units are inside this selection box by comparing it with their actor location

C++ Layer​

The second part of the logic flow is handled in C++ code, starting in the AC_CPP_SelectionSystem_Abstract.cpp file. This layer:

  • Performs efficient entity queries to find units within the selection area
  • Manages selection state across frames
  • Handles selection modification (adding/removing units from selection)
  • Updates UI to reflect current selection

Selection Features​

  • Multi-unit selection via drag selection box
  • Entity querying for efficient selection operations
  • Selection state management across frames
  • Modifier key support for adding/removing units from selection

Usage​

The selection system is automatically set up when using the provided Player Controller and game mode. The AC_SelectionSystem_Basic component handles all the UI interaction, while the C++ layer manages the underlying entity selection logic.

Configuration​

Most selection behavior is configured through the AC_SelectionSystem_Basic Blueprint component. You can adjust:

  • Selection box visual appearance
  • Selection area detection thresholds
  • Modifier key bindings

Troubleshooting​

Selection not working​

  • Verify that AC_SelectionSystem_Basic is attached to your Player Controller
  • Check that the selection system component is properly initialized
  • Ensure units have the correct tags or components for selection detection

Drag selection not selecting units​

  • Verify that units are within the selection box bounds
  • Check that units have proper collision or selection components
  • Ensure the selection system can query entities correctly