DFOV (Digital Field of View) implemented according to specification at http://roguebasin.roguelikedevelopment.org/index.php?title=Digital_field_of_view_implementation. This fast version of the algorithm, based on PFOV, has AFAIK never been described nor implemented before.
Calculates the list of tiles, in
Bump coordinates, visible from (0, 0),
within the given sight range.
Compare steepness of
(p1, f) and
Debug: Verify that the results of 2 independent checks are equal.
The X coordinate, represented as a fraction, of the intersection of
a given line and the line of diagonals of diamonds at distance
d from (0, 0).
Debug functions for DFOV:
Debug: calculate steeper for DFOV in another way and compare results.