Drag points. POSITIVE: when the quantities x2-x and y2-y are both positive or negative NEGATIVE: when one of the quantities x2-x or y2-y is negative ZERO: when the line is flat UNDEFINED/*INFINITY*: when the line is vertical The slope can be thought as steepness. Say you have a wagon on the point (x, y). Now you push the wagon to (x2, y2), and let's say that gravity s along the y-axis. It would be very easy to push the wagon along the line if it was really close to or exactly flat, but really hard if the line was really close to vertical. If the line is slanted downward, you wouldn't need to push; the wagon would start rolling down. At vertical, it would be almost impossible (unless you have some kind of shoes.
While reading my math textbook, I was also working on screen culling for lines (off-edge screen drawing) and I happened to be learning about slopes on lines! So I realized that this slope thing would help in screen culling, but first I will show you a slope.
