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Date: Thu, 18 Feb 2016 23:47:18 -0500
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From: DJ Delorie <dj AT delorie DOT com>
To: geda-user AT delorie DOT com
In-reply-to: <alpine.DEB.2.00.1602190457580.7885@igor2priv>
	(gedau AT igor2 DOT repo DOT hu)
Subject: Re: [geda-user] djopt: what does it do?
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Precedence: bulk

> So removing U and decreasing overall trace length is for 90 degree joints 
> only? Example: http://igor2.repo.hu/tmp/djopt1.pcb

Right.

> The above change is made by debumpify and not unjaggy, right? What's the 
> diff between unjaggy and debumpify? Especially, what'd be a good example 
> where unjaggy would make modifications?

Consider a trace that goes up-left-up-left-up-left, it turns it into
just up-left if it fits.

> Doesn't djopt(auto) run miter? I thought auto ran all opts. Or is 
> it "all-but-miter"? Example: http://igor2.repo.hu/tmp/djopt2.pcb

All-but-miter since the optimizer itself ignores 45-degree corners.
You can run the "auto" optimizer often during layout, then miter as
the last step.

> Does the via remover try to remove unnecessary bridges on the other layer 
> or only vias that literally touches only one thing? Using this example I 
> couldn't decide; it's also unclear why it leaves 3 vias instead of 0 or 2: 
> http://igor2.repo.hu/tmp/djopt3.pcb

Both.  Run it multiple times :-)

Note that "auto" runs all steps over and over until nothing changes.

> Shouldn't vianudge move the via left on this one: 
> http://igor2.repo.hu/tmp/djopt4.pcb

It would if doing so eliminated one of the traces.  Like if that
back-side trace went left a little, then down, it would move the via
to that corner.  In your example, it's not able to remove a corner.

> What'd be a good example case for orthopull?

Consider a horizontal trace with three vertical traces connecting to
it, one above and two below.  orthopull would move the horizontal trace down
to reduce the overall trace length.