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Date: Wed, 9 Jul 2014 18:23:00 -0400
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From: DJ Delorie <dj AT delorie DOT com>
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In-reply-to: <53BDBC7A.5070709@sonic.net> (message from Dave Curtis on Wed, 09
	Jul 2014 15:04:42 -0700)
Subject: Re: [geda-user] pour clearing around pads
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> > * board-level fill
> > * board-level cut
> > * footprint-level fill
> > * footprint-level cut
> > * traces
> I agree with all that.  The need for a footprint-level version of the 
> layers distinct from the lay-out level isn't extremely clear for me, but 
> I assume that makes internal operations easier to sort out.

It doesn't need to be footprint-vs-layout, it's just that there needs
to be rules about how to apply layered patterns when recursively
defining layouts in terms of sub-layouts and/or footprints.  I.e.
the above list is, internally, simply:

* positive, polygons, lines, etc
* negative, polygons, lines, etc
* sub-part (from footprint, sub-layout, whatever)
	* positive, etc
	* negative, etc
	* positive, etc
* positive, etc

> And what are the chances of this happening in pcb?  Is that a doable
> change?

Someone would have to have the drive and time to do it.  I think it's
a fundamental change to the pcb internals, which means it touches most
of the code.

> So here is another one.  I saw my KiCad-using friend (at the "Wednesday 

In some EDA packages, the footprint includes some "skyscraper"
information that gives a rough idea of space needed in 3-D terms.
Sometimes that info can be used to do a 3-D model of the layout,
sometimes that info is used as a 3-D "keep out".  We could define a
type of that data that means "remove board here" but I'm not sure how
well that would relate to the rest of PCB.

I mean, lots of places in pcb need to know the "shape of the board".
Now we're adding "shape of the board from layer X to layer Y" etc.
How much of this shape will be dynamically computed by scanning the
layout?  How much will be pre-computed and cached?  How will this
affect performance or code readability?  I don't know the answers to
those questions.