Re: gEDA-user: Vias with zero clearance in PCB?

[DJ Delorie <dj@xxxxxxxxxxx>]

> The reason is that non-quadrant arcs necessarily fall off of the
> grid - in principle you can't move your crosshair their. Now that we
> can snap to line/arc endpoints, this really isn't an issue, so we
> can consider a more advanced arc drawing tool.

I didn't say it would be easy.  Drawing programs often offer multiple
ways to draw just circles; arcs add a whole new complexity to it.  I
can't think of a good way to have the user create non-quadrant arcs,
but moving endpoints afterward might be doable.

> PCB can also handle skewed arcs (unequal horizontal and vertical
> axis), but that isn't supported by the gerber standard, so I proved
> no way to draw them. Some of the very old libraries still do that
> though.

We can, at worst, convert them to line segments if we have to.

> Which would have to be on a per-layer basis too. Personally I think
> we should add an array of say 2 bit numbers for each layer to
> indicate what style of thermal should be used on that layer. We
> could offer 2 finger rotatations, solid fill, or no thermal that
> way.

Sounds reasonable.  Fortunately, we use symbolic flags, so we can add
them as new flags without breaking backward compatibility :-)

We currently have:

thermal(1,2,3)  - thermals on layers 1, 2, and 3.

We can either annotate the layers:  thermal(1+,2s,3)  +=rotated, s=solid
or: thermal(1:rot,2:solid,3)

or add a new flag name: rthermal(1) sthermal(2) thermal(3)

> I think it would be nearly useless. Most boards these days have both
> power and ground planes, so the vias had better clear some polys.

Well, *yeah*.  I meant connected vias, it would have to be part of the
thermal tool.  Any via with a thermal would be solid with this flag.
If we do the two-bit thermal flags, this global flag would only change
the default for new vias.