> At 09:00 AM 5/15/01 +1000, Ian Wilson wrote:
> >Also, for a number of reasons we have decided that supporting undo of the
> >inversion is not an option for us.
>
> Running the inversion twice with the same reference line should
effectively
> undo it. That, in fact, would be a good (though partial) test of the
> accuracy of the inversion. A doubly-inverted file -- unless you put some
> flags in it -- should be exactly the same as the original file.
>
> Abdulrahman Lomax
Differences between a non-inverted PCB and a doubly-inverted PCB could occur
if the user selects the (to be provided) option of repouring polygons within
the PCB during either or both inversions. (If the user selects the
alternative option of *not* repouring polygons, and does so for *both*
inversions, the two PCB files *should* be the same.)
The inverting procedures could have an impact upon the internal sequences of
primitive objects (Arcs, Fills, etc), which could translate into differences
in the internal contents of each PCB file. That consideration could also
have an impact upon output files (NC Drill files, Gerber files, Pick'n'Place
files, etc) generated from each PCB file, though if such (output) files were
to be viewed or printed out (from the viewing utility) (or sorted in the
same manner, in the case of Pick'n'Place files), then they should be
identical in that regard.
And in the event that the user selects inversion through an axis whose angle
is *not* an integral multiple of 45 degrees (which will be supported, either
from the start, or otherwise at a later stage), rounding considerations
could have an impact upon the locations of primitives within the (doubly
inverted) PCB file. That said, this is unlikely to have a *practical* impact
upon this PCB file, but users might notice (small) offsets in the locations
reported by the primitives' dialog boxes in some cases. (These offsets
*shouldn't* occur if the user selects an axis whose angle *is* an integral
multiple of 45 degrees, and in normal circumstances, users *would* want to
select such an angle.)
Without violating the NDA aspects of the SDK files, the decision to not
support undoing inversions was made because Protel's implementation of
undoing commands is flawed in some aspects, including (but not confined to)
polygons. If the undo procedure was to be partially supported, and users
then attempted to use it, they would risk turning their PCB file into a
pig's breakfast. As such, the "right" way to undo an inversion is to invert
the PCB file a second time, or else to close the file without saving this
first, assuming that the user last saved the file immediately before
inverting this.
In actual fact, given our joint decision to not support undoing the
inversion procedure, we envisage providing an user interface in which the
user will be warned that undoing the inversion procedure is not supported,
and providing an opportunity for the user to save the file first (or to save
a copy of this with a different name). (And for those who know what they are
doing, we also envisage providing support for a parameter so that the user
can invoke the inversion procedure *without* having this warning, and
associated aspects, displayed beforehand.)
Regards,
Geoff Harland.
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