Use turbo mode to draw faster. Click the button to edit the number. Pick a positive whole number that's not too big. A bigger number will lead to more different possible slopes and will cause a lot more lines to be drawn, and it might lag a lot. If your number is >5 or so all the detail will be hard to see. When using custom slope, make sure that the two numbers are relatively prime, both positive, and 0<x<y. Try (390,989) (1245,2356)
Many lines with different starting slopes are drawn, one for each different fraction the program checked. Lines are drawn starting from the center point. There is an imaginary grid of vertical and horizontal grid borders (if the grids aren't too tiny, red lines will be drawn to represent these), and every second time a line hits one of these, it will bounce. Lines end when they hit whole points.
