[Freeciv-Dev] Re: directional system: more magic code cleanups

[Raimar Falke <hawk@xxxxxxxxxxxxxxxxxxxxxxx>]

On Mon, Sep 17, 2001 at 11:13:03AM +0100, Gregory Berkolaiko wrote:
>  --- Jason Dorje Short <jshort@xxxxxxxxxxxxx> wrote: 
> [..]
> > It does *not* fully fix dir_ok and straightest_direction as it should;
> > I
> > think Ross should provide a patch that fixes these guys properly. 
> > However it is good as far as it goes.
> 
> there is a nice mathematical way to code dir_ok:
> if diff_x, diff_y and dir are what they are in the current function then
> the "scalar product"
> 
>         diff_x*DIR_DX[dir] + diff_y*DIR_DY[dir]
> 
> is positive whenever direction is ok.  And you don't need any switches.

Very nice. Good spotting. For clarity: s/positive/>=0/. There may be
extra documentation about this (for a given diff vector there are
exactly 5 directions ok. These are centered around the given diff
vector. The "outmost" still valid directions are orthogonal to the
given diff vector. scalar product bla bla ...)

> However Ross' patch might be more advanced than this.

No I don't think so ;)

        Raimar

-- 
 email: rf13@xxxxxxxxxxxxxxxxx
 "I was dead ... but I'm better now."
    -- Capitain Sheridan in Babylon 5