[MPlayer-dev-eng] [PATCH] Fix conversion for v4l2 video controls

[Trent Piepho]

On Sun, 16 Sep 2007, Vladimir Voroshilov wrote:
> Hi, All
>
> I hve found some trange conversion in v4l2's set(get)_control
>
> It converts (0-50) range to drivers' (min-default) and (50-100) to
> (default-max).
> (The same is doing for (-100-0) and (0-100) ranges).
>
> Attached patch changes conversion to (0-100) -> (min-max)
>
> Otherwise one of ranges is unsuable for cases when default==min or
> default==max (and even cause devision by zero error).
>
> I'll apply it in two days if nobody will say something against.

mplayer default value for all the controls is 50, so if you change it so 50
is no longer the v4l2 default, then the two won't match.

This will cause a problem with the common cx23880 chip.  The contrast range
for this chip is 0% to 400%, instead of the more common 0% to 200%.  The
v4l2 control ranges from 0 to 255 with a default value of 63.  mplayer
handles this nicely now, as the mplayer control value of 50 gives you the
default 100% contrast with the cx88 driver and with other drivers too.
After your change, 50 will give you 200% contrast with cx88 but still 100%
with other drivers.

The default control value is information the driver is providing about how
to use the hardware, so by ignoring it you're not supporting the hardware
as well as you could.

I think it would be a lot better if you just checked for default==min or
default==max and used the full range in that case, and kept the current
behavior when min<default<max.