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From: "Luis de Arquer (ldearquer AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Date: Sat, 11 Mar 2017 19:39:44 +0100
Message-ID: <CAGqyy=ZPkj82-K6NW9dFSwt7s6LXD92Ka6A1_0OTVYUKYfW2wA@mail.gmail.com>
Subject: Re: [geda-user] Rubberband move keeping lines direction
To: geda-user AT delorie DOT com
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2017-03-11 18:21 GMT+01:00, Nicklas Karlsson
(nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com]
<geda-user AT delorie DOT com>:
>
>> The problem was that, snapping to grid for any
>> angle is perhaps impossible ...
>
> In sort of it is because a double might not hit the exact number in the
> grid. To be perfect they should snap to the same or closest number but in
> practice it might not make a difference.
>
> I think it is great even without this small tiny detail.
>

Actually it was more of an integer geometry issue. We are talking here
about 3 lines, 1 "main" line that we are moving, and two
adjacent/neighbour lines. In order to keep directions while moving,
the main line moves towards/from the point defined as the intersection
of the two neighbour lines -included the case of infinite
intersection, i.e. parallelism.

__  A
     \
      \  B
       |

There are two points A and B which define the main line, and which you
can try to keep
aligned to grid, which is doable for 45/90 lines. However, and this is
my point, I don't think it is guaranteed that they can be snapped
simultaneously on the generic case, where lines can have any
direction. Or even if they can, the first occurrence of such snapping
could well be tens of grid points away. Think of a line with slope
19/1 and another one with slope 1/7.

I am glad you are finding it useful!