Re: gEDA-user: General Layers questions

[Stephan Boettcher <boettcher@xxxxxxxxxxxxxxxxxx>]

Martin Kupec <martin.kupec@xxxxxxxxx> writes:

> On Fri, Mar 18, 2011 at 01:44:35PM -0600, John Doty wrote:
>> >> Trying to model things that aren't layers as if they were layers is
>> >> one common mistake in this kind of tool. Equally common is leaving out
>> >> layers: the insulating layers in a PCB are just as important as the
>> >> copper, and have their own properties (shape, thickness, material,
>> >> etc.). They're a critical part of the layer stack.
>> >> 
>> >> The description language needs to be able to express "feature p in
>> >> layer x is aligned with feature q in layer y" in order to build up
>> >> composites. This is the geometrically sensible way to describe the
>> >> result of drilling through several layers. But the geometric
>> >> description language should not be tied to any particular fabrication
>> >> procedure.
>> > 
>> > This is all too physikal for my taste.
>> 
>> I assert that if you do it any other way, you wind up with the
>> following catastrophe: the code for every layer type needs to
>> incorporate a specific definition of its interaction with the code
>> for every other layer type. A total collapse of factoring, poisoning
>> flexibility and maintainability. But if layers correspond to actual
>> geometric layers, this can be avoided, I believe.

What I like with PCB is that there is very little interaction.  Only
when special actions are called, the interactions are invoked.  E.g.,
when I hit the O key, the connectivity is evaluated.  For that I only
need to know which layers are conductive and what vias connect which
layers.

> Actually what I am trying to do, is to have concept so layers don't
> interract with layers of different type. The composits are a bit
> problem, because I would need to consider more layers when performing any
> action, but I think that it can still be interaction with object on the
> same layer.

I do not understand what problems you see with composits.  A layer
consists of the union of all shapes on any level of the composits
hierarchy.  Composits may be referenced at multiple positions, so those
shapes appear multiple times.  When a shape is modified in a composit,
it may affect all copies simultaniously, or the composit will be
duplicated (copy on write), depneding on an attribute or explicit user
action.

> So, i.e., If we would have 'hole' layer. I would have check, that holes
> on hole layer are not intersecting. And also check the intersection of
> attached shapes on each layer. But all what can happen is that some
> layer will yell that something bad happend and I should cancel my
> action.

Where do you want to attach holes. To layers, like John proposes?  To
shapes on a layer?  Or as independent entities, like they are now?  

-- 
Stephan


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