Ain't they cute?

view = TrailsView.new(
	:width => WIDTH,
	:height => HEIGHT,
	:scale => 0.5,
	:origin => Location.new(-200, -100)
)

This is another prerequisite to a 2D shooter. Scrolling should be a matter of:

View#origin.y -= SCROLL_RATE * clock.elapsed_time

Some kind of factory can spawn enemies from a YAML file as the player approaches them, and delete them after he passes them.