gEDA-user: constructive geometry (was Re: final modification)

[Ethan Swint <eswint.ramu@xxxxxxxxxxx>]

Bert Timmerman wrote:
> Modifying the existing polygon would probably become too cumbersome if
> new vertices need be added and holes ("negative" copper) in polygons to
> be defined in ways currently not feasible within the current pcb file
> format.
>   
Ah - back to the file format. ;)  Would it be difficult to add in a 
final "positive/negative" argument to the polygon definition, which, if 
absent, defaults to "positive"?  (I think I already know the answer, but 
yet I ask...)
> BTW: would the "OR" operation result in an overlapping polygons, would
> the "AND" operation result in the intersection of two polygons, and
> would the "XOR" operation result in "negative" copper (a.k.a. a hole)
> where two polygons were overlapping and leave "positive" copper where
> only one of the two former polygons touched the laminate ?
>   
The AND and OR of two overlapping polygons would both end up with a 
single, final polygon, e.g. square AND circle => a quarter circle; 
square OR circle => circle with a square protruding from it.  XOR could 
result in a "negative" copper space, if one geometry is completely 
contained within the other; square XOR circle => square w/ circular hole 
(a la square pin for a component).  Otherwise, the geometry would be 
broken into two new geometries, touching at the former intersection 
points, square XOR circle => 3/4 circle and all that's left of the 
square is an "arrowhead" shape.

I wonder how the code presently handles the "negative" copper that 
results from a pad/track/via that has the "clears polygon" flag set?

-Ethan


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