getOpFromAction( mouse, key ) {

		let action;

		for ( let i = 0; i < this.mouseActions.length; i ++ ) {

			action = this.mouseActions[ i ];
			if ( action.mouse == mouse && action.key == key ) {

				return action.operation;

			}

		}

		if ( key != null ) {

			for ( let i = 0; i < this.mouseActions.length; i ++ ) {

				action = this.mouseActions[ i ];
				if ( action.mouse == mouse && action.key == null ) {

					return action.operation;

				}

			}

		}

		return null;

	}
Return the operation associated to a mouse/keyboard combination.

@private
@param {0|1|2|'WHEEL'} mouse - Mouse button index (0, 1, 2) or 'WHEEL' for wheel notches.
@param {'CTRL'|'SHIFT'|null} key - Keyboard modifier.
@returns {'PAN'|'ROTATE'|'ZOOM'|'FOV'|null} The operation if it has been found, `null` otherwise.