Re: gEDA-user: next PCB release - 1.99za vs 4.0

[DJ Delorie <dj@xxxxxxxxxxx>]

> > With flex cable, "top" and "bottom" aren't limited to one layer each.
> 
> Aren't they?

No.  Different areas of the cable may have extra layers or pcbs
attached, changing the number of layers in that area.  So one drawing
layer might be "top" on the left side of the cable, but "inner" on the
right side.

> What use case is there for layers that map to multiple physical layers?

Single solder mask for both sides.  Keep-outs.  copper heatsinks.
stripline.

> I did not consider layers that are not mapped to physical layers, except
> the rats layer. I think the best way to do this would be to have another
> class of layer group:
> 
>   Top, Bottom, Inner, Outers, None

How does "none" map to your physical tree structure?

> > Why one?  Why not save it?  We already save rats to file.  What about
> > layers that don't correspond to a physical layer?
> > 
> 
> Why have a different number than one? I could not think of a good reason
> for this.

autorouter might use it to store information.  DRC might.  I don't
know what future uses, it just seems that "one" is a special case.
Why not just have a "save me" flag, and let each layer decide if it
needs to be saved or not?

Paste buffers (cut-n-paste, not solder paste) might need multiple
temporary layers.

> > keepouts are just another layer.  Let DRC worry about what to do with
> > it.
> 
> Ah, but what happens when you want a keepout on all layers? On one layer?
> For only HV lines? For footprints but not traces? All these have been
> mentioned on the list, and don't work well with "keepouts are just another
> layer".

I meant, if you have a keepout layer, it's just another layer.  I
didn't mean to imply that there weren't other ways to specify
keepouts.


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