Clip the line pts[0]โฆpts[1] against clip, ignoring segments that
lie completely above or below the clip. For portions to the left or
right, turn those into vertical line segments that are aligned to the
edge of the clip.
Intersect the line segment against the rect. If there is a non-empty
resulting segment, return true and set dst[] to that segment. If not,
return false and ignore dst[].
Returns value between the two limits, where the limits are either ascending or descending.
Returns X coordinate of intersection with horizontal line at Y.
Returns Y coordinate of intersection with vertical line at X.