you can use the overlay object to do a number of things that drawline could do, as well as many more complicated, thought it may tax your system if you use it too much at a time, and its a tad complicated. Use it in conjunction with the active overlay object for scrolling.
Unless I turn debug mode on it doesn't seem to do anything but obscure background objects in the frame editor. With debug mode on, it continues to obscure my view, except for when I run the game it continues covering my view. The lines will be drawn with debug mode on, but then there's a nice blob of color surrounding the whole background.