First of all, yes, this can be helpful or annoying, depending on what one 
is trying to do.

For those popping into this thread, here is a description of the problem. I 
want to review the layers of a board for route quality, so I want to look 
at one layer at a time. Or perhaps I want to look, on a complex board, for 
an open routing path on a particular layer, and to draw a trace down that path.

There are two ways to do this; one is to enable single layer display mode, 
the other is to disable all layers except for the one I want to examine 
plus "multilayer," the annoying superfluous layer that Protel has inflicted 
on us, and possibly an outline layer. (It had a reason for existence at one 
time, but that time is past). Either way produces the same display (I'm not 
sure there are no exceptions, but they looked the same to me when I just 
checked it.) (There is an option to include selected mech layers in 
single-layer mode, I think it is in the mech layer setup dialog.)

However, Protel has an excellent feature. When you attempt to route (Place 
Interactive) a track, and start your route in contact with any copper, the 
route not only picks up the net of the copper, if any, but it also 
highlights all copper with the same net. Regardless of what layer this 
copper is on and whether or not that layer is display enabled.

I would argue that this should be a disablable option, or, perhaps, it 
should not happen in single-layer mode. I prefer the former.

But it cannot be disabled, as far as I could find.

The highlight is not in the color of the track, so the suggestion to set 
the offending layer color to the background is actually the opposite of 
what one should do: set the layer color to the complement of the background 
color, since highlight is naturally the complement. So for a black 
background, a layer set to white will appear as black when highlighted. 
However, such track *also* has the focus, which means that it is outlined. 
You can still see it, it is just not quite so blatant.

It is not necessary to redraw the screen to remove the highlight; all that 
is needed is to click anywhere in empty space in the workspace and the 
highlighted track from other layers will disappear. But, obviously, if you 
are routing, the current net is highighted, period.

For inspection purposes, however, turning off the highlight by removing the 
focus from any net by clicking on empty space will suffice. One can then 
inspect all the layers in sequence, and for this single-layer mode is best. 
If it is necessary to reroute a track, normally the highlighting will not 
be *too* annoying, and it is one click to remove it.

There is another shortcoming of the Protel display routines. Vias are 
intrinsically multilayer, yet blind and buried vias only appear on a 
limited number of layers. Protel does not correctly display this. I would 
suggest that multilayer *not* be part of the single-layer view; rather, a 
multilayer pad or via would be checked for presence on the view layer and 
would not appear if it was not present.

(Right now there is no such thing as a blind or buried pad. That too is a 
shortcoming; basically, the pad/via distinction is largely artificial; I 
would have a pad attribute called "via," which would identify the pad as 
being used for routing only and not for mounting; free pads by default 
would be vias. Pads are better than vias because it is easier to define 
special rules keyed to the pad name whereas vias have no names. Yes, you 
could have square-pad vias. Why not? Allowing blind pads would simplify 
via-in-pad design.)

Abdulrahman Lomax
Easthampton, Massachusetts USA

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