Arrow keys for navigation + and - keys for zoom The "Mouse Coordinates" variable displays where your mouse is relative to the grid The prompt at the beginning is asking for two points on a grid: x1 being the x of the first point, y1 being the y of the first point, x2 being the x of the second point, & y2 being the y of the second point.
This is very unoptimized. I limited to zoom to a certain point because it gets so slow.
