compare two points based on minPoint (the upper/leftmost point).
compare two points based on minPoint (the upper/leftmost point).
given a Y coordinate we should be able to calculate what the X coordinate would be along this line.
given a Y coordinate we should be able to calculate what the X coordinate would be along this line. if the line was (0, 0) -> (4, 6), then getx(3) would return 2.
this represents a line segment from p1 -> p2. there are no assumptions about p1's relationship to p2. we determine pmin (the point whose Y coordinate is least (with lowest X coordinate used as a tie-breaker) and pmax (the opposite) for when we need to know which is least or greatest. we order lines by "lowest" pmin.