Scan line indicator for ZBar overlays

Zbar is a great tool but I often struggle with adding intuitive graphics to the overlay screens in order to clue-in the users to the fact that scanning has already begun in video mode and they just need to point their camera at a barcode. To that end, I've decided that a red colored line dragging up and down on the screen is a great way to get the point across. And the code applies to any scanning framework that lets you mixin an overlay, not just ZBar.