Re: gEDA-user: "mm garbage", cannot repro

[Ben Jackson <ben@xxxxxxx>]

On Thu, Nov 20, 2008 at 01:01:12PM -0500, DJ Delorie wrote:
> 
> > As far as I can tell the problem with _/ mode is that you're drawing
> > a _/ with a degenerate `_' segment.  You won't get the garbage in `X'
> > mode.  So it's not the 45s themselves that are the problem.
> 
> Right, the problem is that the grid points aren't exactly 45 from each
> other, so _/ mode thinks it needs a diagonal and a straight to get
> there.

It does need a diagonal and a straight to get there.  My proposal (1) was
that it skip the straight under certain conditions.  Other proposals have
been to tweak the 45 so it actually lands on the grid point.  These are
basically equivalent in terms of the code required.  I think it's better
to make a truly 45 degree line.

BTW a back of the envelope calculation suggests that if the grid math
worked in the "obvious" way that this sort of error shouldn't turn up
except in rare circumstances where the diagonal line crosses a roundoff
error (which by my estimate should happen about every 12.7cm) in one plane
and NOT the other.  Since it happens more often there's probably a bug in
the grid's math.

-- 
Ben Jackson AD7GD
<ben@xxxxxxx>
http://www.ben.com/


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