[Freeciv-Dev] Re: [PATCH] Cleaned up magic code ingotohand.c (PR#944)

[Jason Dorje Short <jshort@xxxxxxxxxxxxx>]

"Ross W. Wetmore" wrote:
> 
> dir_ok and straightest direction are both buggy in the same way.

Actually, I think straightest_direction has an extra bug.  Even if
you're moving directly in a cardinal direction, it will move you
diagonally if possible.

> The best thing is to replace them, not fix magic numbers and then
> throw out the fixes when you replace the whole routine :-).

They definitely need to be replaced.  However, fixing the magic numbers
is so easy there's no reason not to do it first.

> However, I wouldn't even do this patch until you apply the rotation
> direction patch, as it doen't really gain you anything.

Huh?  Do you mean this patch I submitted?  It gets rid of the magic
numbers, making the code more stable and easier to read.

> The algorithm in the corecleanups works by dividing the full square
> into 8 octants using the 2x+y, 2y+x, 2x-y and 2y-x lines as borders.

Well, that's a good algorithm.  It's hard to understand from your
diagram and paragraph, but I agree entirely with what you're saying.

straightest_direction has units currently moving like this for goto
routes:

X is a unit
Y is the target
* is the route

X     Y
 *   *
  * *
   *

In other words, it strongly prefers to move on a diagonal.  Your
algorithm would correct this behavior.


However, I think an even better algorithm might be possible.  Your
algorithm is a huge improvement, but will still result in the unit
traveling in either a cartesian direction or a diagonal one to get to a
place where it's a straight cartesian/diagonal route:

  
X****
     *
      *
       Y

or

X
 *
  *
   *
    ***Y

The "best" algorithm, I think, would have a unit traveling into as close
to a straight line as possible:

X
 **
   **
     **
       Y

I believe this algorithm would be substantially more complicated,
though, whereas yours should still be pretty simple.


jason