VASSAL Reference Manual

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Trigger Action Trait

This trait alters the behavior of a piece, but not its look. Using it, you can combine multiple keyboard commands into one, or automatically fire keyboard commands in response to other keyboard commands when certain conditions apply.

Trigger Name: Short name for identification purposes.
Trigger when properties match: The corresponding key commands will be performed only if the piece matches this Property expression (after the triggering keyboard commands have finished)
Menu Command: Adds an item to the piece's right-click menu that will fire the triggered commands (provided the property expression is matched).
KeyStroke: The keyboard command corresponding to the menu item.
Watch for these Keystrokes: After the user types any of these key commands, fire the triggered commands if the property expression is matched.
Perform these Keystrokes: The key commands to invoke after one of the above key commands is observed and the property expression is matched.

Example: A piece has a Layer to track action points and a Move Fixed Distance trait to move it forward. The Move Fixed Distance trait can be assigned the key command CTRL-SHIFT-M with no command name (so that it does not appear in the right-click menu). Then a Trigger Action trait with the command Move and the keystroke CTRL-M can trigger both the Move command and decrease the action points layer by one.

Example: A piece has separate Layer traits for hit points and for a "critically wounded" status for when the hit points are less than 2. A Trigger Action trait can watch for the keystrokes that affect the hit-point layer and respond by activating the wounded layer by matching the property expression for when the hit points are < 2 and the wound level is not active.