[BRLTTY] skipping broken cells

[Dave Mielke]

[quoted lines by Aura Kelloniemi on 2019/05/14 at 16:52 +0300]

>It would be quite a coincidence, if they had the same cells broken.

Yes! :-)

>Also, most often the whole cell is not defunct, but some particular dots are.
>BRLTTY could take this into account and still use the broken cell if the
>broken dots are not needed in the braille pattern that is to be written to the
>cell.

This implies that brltty would sometimes use, and at other times not use, such
a cell. This'd cause the output from that cell onward to shift back and forth,
which, in my opinion, would become very confusing. I think it'd be far better
for brltty to simply skip over such a cell so that the user never has to guess
at what's going on.

>And what should BRLTTY write to the cells which the user has reported as
>non-working? Should they be left empty (which might lead to confusion about
>whitespaces) or should all (working) dots be raised up? Maybe this would be
>configurable, because marking defunct cells already requires configuration.

I think it should be configurable as each user will prefer something different,
and also because it may well depend on how a given cell is deffective.

>Some devices probably allow their serial number to be queried, which at least
>in theory could be used to choose the correct list without user intervention.

That's an excellent idea!

>Currently I'm lucky not to have a single broken dot in my display, but I have
>another issue which could potentially be solved by this feature. When the
>battery of my Focus Blue is low (<=10%), the firmware writes a status
>indicator at the righthand side of my display. This indicator cannot be
>disabled and it is shown all the time. The firmware uses dots 7 and 8 in this
>indicator (which is 1-5 cells wide, depending on the battery status).
>Unfortunately I use a braille table which extensively uses dots 7 and 8, so
>the battery status indicator completely garbles all characters in the last
>five cells. Currently I work around this issue by setting Window overlap to
>the width of the status indicator whenever this problem appears. But I would
>prefer to have those cells be filled with the pattern ⣿ (all dots up). This
>would be much less confusing than having garbled text at the end of each
>braille window. 

In your case, I'd suggest listing those cells as deffective and to be filled
with just dots 1-6. That way, you still get your indicator.

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