Re: gEDA-user: More on the polygon bugs

[Steven Michalske <smichalske@xxxxxxxxx>]

I was making some symbols the other day and saw that the mask was  
allowing exposed copper to be shown.

I have some thoghts on the rounded corners...   Can we get the pads to  
have similar rounded corners?

Thanks for your efforts.

Steve

Sent from my iPhone

On Jul 29, 2007, at 12:35 AM, Ben Jackson <ben@xxxxxxx> wrote:

> I've now officially spent way WAY too much time looking into this, but
> here's what I've found:
>
> The problems happen when the polygon clearing code tries to remove a
> region.   In this case, a temporary rounded rectangle with the shape  
> of
> a pad + clearance.  A line in the existing polygon (the remaining part
> of the partially cleared copper polygon) that SHOULD intersect this
> polygon does not.  So a line which should get a new vertex in the  
> middle
> stays whole.  Then, inside some code I still haven't tried to figure
> out, the attempt to collect the new set of contours and holes goes  
> wrong
> because of the missing vertex (the line can't be trimmed right).
>
> The reason the lines do not intersect is that the FIRST time the pad
> was cleared (remember, the first thing I found to avoid this was to  
> fix
> the multi-clearing of pads), two lines fully crossed in an 'X'.  A  
> point
> in an *integer coordinate system* was chosen to be the crossing point.
> Each line is now two lines, going to that point.  So far, the roundoff
> isn't that scary.  In the trimming, X becomes something like > (with
> some of the segments deleted).  Now the duplicate subtraction comes
> along to intersect > with /, only the point of the > doesn't actually
> quite reach the /, so the / doesn't get split into two segments.  Then
> you get problems.  Trying to bandaid that causes problems by creating
> duplicate intersections elsewhere.
>
> Part of the reason this happens so often is that there are a lot of
> lines floating around with verrrry shallow angles just off vertical or
> horizontal.  That causes the rounding of the intersection to be much
> more significant in the shallow axis.  Where do these lines come from?
> Back to the duplicate pad subtraction...  It turns out RoundRect (and
> most things that call frac_circle) generate slightly wonky polygons.
> frac_circle doesn't turn quite 90 degrees, so the sides of the pad
> clearances are all slightly twisted.  This caught my eye while I was
> looking at polygons at about 10000% magnification to see intersection
> points and I didn't realize the mathematical implications of the
> asthetically displeasing corners for a while.  If you fix RoundRect,  
> you
> can even get away with some double-pad-subtraction that blew up  
> before,
> becuase the resulting horizontal and vertical lines are less prone
> to rounding errors when intersected with other lines.
>
> If you have boards that still cause problems after applying the multi-
> pad-sub patch I sent out, mail them to me and I'll see if this fixes
> them.
>
> (by the way, holes in the mask aren't rounded, so there's another  
> reason
> to tighten up your masks!  A perfectly aligned mask equal to the  
> clearance
> would *always* leave an arc of copper exposed).
>
> -- 
> Ben Jackson AD7GD
> <ben@xxxxxxx>
> http://www.ben.com/
>
>
> _______________________________________________
> geda-user mailing list
> geda-user@xxxxxxxxxxxxxx
> http://www.seul.org/cgi-bin/mailman/listinfo/geda-user


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