 = indexOf(obj, x, y)
            % Check if empty first
            if isempty(obj.stack)
                clicked = -1;
            else
                in = find(obj.stack(:, 1) == x & obj.stack(:, 2) == y);
            
                if isempty(in)
                    clicked = -1;
                else
                    clicked = in;
                end
            end
        end
        
        %% addClickToStack
        % Adds an (_x_, _y_) coordinate to the stack *unless* it does not
        % a