> >>There are problems with doing X and Y flips - they don't swap layers and
> >>they leave components in upside-down. The L-Flip (layer flip) with
> >>selections is also fraught.
> >
> >What purpose does X & Y flip serve with respect to the components
themselves
>
> X and Y flip of components is supported to ensure there is a steady flow
of
> new users with very difficult to mount components.

Toggling the mirrored status of components (with the X and Y keys) is an
aspect of Protel going as far back as the DOS versions (of both the
schematic and PCB applications). (With hindsight, perhaps the X and Y keys
should always have "inverted" (PCB) components instead of reflecting these,
but in the days of the earliest DOS versions, through-hole components were
still the norm, and while it eventually became possible to "invert" such
components (along with SM components), reflecting (PCB) components following
the use of the X and Y keys had (instead) become the norm by then.)

There are pros and cons to being able to mirror components. It is not
totally out of the question that users will continue to be warned (in
Phoenix) whenever they are about to toggle the mirrored status of one or
more components, but another two alternative scenarios are that mirroring of
components will no longer be supported, or else (I hope) that Component
objects (like String objects) will incorporate a (Boolean) Mirrored field.

No longer supporting mirroring of components could have disagreeable
ramifications when it comes to reflecting selected objects; consider what
currently happens when the L key is pressed. (Not exactly the same, to be
sure, but still indicative of what could come about.) OTOH, the provision of
a Mirrored field for Component objects would permit users to determine, as
required, whether any components in the PCB are currently mirrored, and
users could be warned of the presence of any such components whenever they
initiated any generation of Gerber files, NC Drill files, etc. (They would
either have the option of aborting the generation of those files at that
time, or else continuing, not dissimilar to the present situation whenever
an attempt is made to reflect one or more components.)

> >apart from sorting out assembly layer issues for components on the bottom
> >layer ie. allowing you to move the mechanical bits to another layer and
> >mirroring them when necessary. Put another way, wouldn't it be better,
> >even now, to define a set of properly paired layers and (harking back to
> >my original point) to make sure that ALL future layers are paired.
>
> I really do not want forced pairing of all layers.  When doing some
> documentation I want to be able to refer to a specific layer and know that
> the details I am referring to are indeed on that layer.  Forced pairing
> would limit flexibility.

I fully agree. That is why I have always suggested that any pairing of Mech
layers should be user-configurable.

> *But*...there is a possible source of new confusion that will arise when a
> design has its layer pairs modified mid stream.  This could progressively
> cause items to become scattered around on multiple different layers -
there
> is something to be said for the safety of fixed layer pairings.  (Also, if
> layer pairings can be set in the PCBLib, what happens when a component is
> brought into a design with different pairings?).

Such considerations have also occurred to me in recent times, which is why I
have more recently suggested that perhaps entirely new layers should be
provided instead, and with the pairing of these being of a fixed nature.

> How are issues like this handled in other packages?
>
> bye for now,
> Ian Wilson

My recollections of PCAD AD2.0 (an earlier DOS version) are that there were
a considerable number of pre-defined layers, along with pre-definined
pairing of many (but not all) of those, and PCB Library files provided by
the then-existing PCAD incorporated (primitive) objects using the same
layers and layer pairings. Users could create their own PCB Library files,
and with their own layers and layer pairings, but in the absense of
compelling reasons to the contrary, it made good sense to use the default
layers and layer pairings, and to avoid the use of yet other layers (or at
least within PCB *Library* files).

I can not comment on other CAD packages, other than to say that P-CAD 2001
does not permit users to pair user-defined layers to one another (and as
such, that is a loss of functionality compared with at least some previous
versions of PCAD). (There are five pairs of pre-defined layers, of which
eight are similar to the paired layers currently provided in Protel, with
the other pair being Assembly layers. The only other pre-defined layer, the
Board layer, is of an unpaired nature.)

I am not sufficiently familiar with current versions of Autocad to comment
on whether layers can be paired to one another in any way, and I don't
remember or know whether the earlier versions supported that or not. (When I
used Autocad to design PCBs, these all incorporated *just* Top side
through-hole components, so I had no reason to investigate whether layers
could be paired to one another, or whether objects could be "inverted" in
any fashion. That said, while I didn't acquire any expertise myself in using
any type of scripts with Autocad at that time, it is still probable that
suitable scripts could have been (and, if necessary, still be) written to
implement personalised pairing of layers and "inversion" of objects.)

Can anyone else comment on these issues with other applications?

Regards,
Geoff Harland.
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