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Date:	Wed, 9 Jul 2014 13:50:41 -0400
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From:	DJ Delorie <dj AT delorie DOT com>
To:	geda-user AT delorie DOT com
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	(message from Peter Clifton on Wed, 09 Jul 2014 13:50:00 +0100)
Subject:	Re: [geda-user] pour clearing around pads
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> I think any layer objects embeded in footprints (might as well include silk and copper in the same way  going forward), ought to reference predefined symbolic layer name or ID.
> 
> "TOP-SILK" "TOP-MASK" "TOP-COPPER" "INNER-COPPER" "INNER-ANTI-COPPER"* "BOTTOM-COPPER" etc...
> 
> *(inner anticopper might need some thought, possibly not one for today!).

Yeah, IMHO symbolic layers is a must.

I also think we need a way of "stacking" or "nesting" drawing layers
within a physical layer to do fill/cut/draw operations.  For example:

* "Fill" - positive, first rendered, used for power plane polygons
* "Cut" - used for keep-outs, and cutting planes into sub-planes with traces
* "Trace" - used to draw traces over polygons (clear polygons but ignore cuts)

Each layer needs a positive/negative flag, so you could (for example)
draw negative text over a filled rectangle.

But given that footprints might have their own fill/cut/trace layers,
which may be drawn on top of the board-layer cuts, we need to be
flexible in making these stacks...

* board-level fill
* board-level cut
* footprint-level fill
* footprint-level cut
* traces

but if you want to support "sub-layouts" it gets even more complex.

Perhaps a heirarchical design?

* board-level fill
* board-level cut
* sub-layouts and footprints ->
  *  . . .
  *  . . .
  *  . . .
* board-level traces

And all that is just *per layer*

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