On 04/05/2009 02:58 PM, Erik Andrén wrote:
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Hans de Goede wrote:
On 04/05/2009 01:26 PM, Erik Andrén wrote:
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Hans de Goede wrote:
On 04/04/2009 10:22 PM, Erik Andrén wrote:
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Hi,
While trying to get hflip and vflip working for the stv06xx webcam
bridge coupled to the vv6410 sensor I've come across the following
problem.
When flipping the image horizontally, vertically or both, the sensor
pixel ordering changes. In the m5602 driver I was able to compensate
for this in the bridge code. In the stv06xx I don't have this
option. One way of solving this problem is by changing the
pixelformat on the fly, i. e V4L2_PIX_FMT_SGRB8 is the normal
format. When a vertical flip is required, change the format to
V4L2_SBGGR8.
My current understanding of libv4l is that it probes the pixelformat
upon device open. In order for this to work we would need either
poll the current pixelformat regularly or implement some kind of
notification mechanism upon a flipping request.
What do you think is this the right way to go or is there another
alternative.
The changing of the pixelformat only happens when you flip the data
before conversion. If you look at the current upside down handling
code you will see it does the rotate 180 degrees after conversion.
This is how the vflip / hflip should be handled too. We only have
4 (2 really since we don't care about r versus b / u versus v while
flippiing) destination formats for which we then need to write flipping
code. Otherwise we need to write flipping code for *all* supported input
formats, not to mention flipping some input formats is close to
impossible
(JPEG for example).
So you mean we should do the vflip/hflip in software, just exposing
one native format?
Erm, yes that is what I was saying, but that is because I was confusing
things with the sq905 driver some other people are working on.
Glad that you were confused as I couldn't really make out the
meaning of your answer. :)
Now I understand what you were trying to ask. So the problem is that
the vv6410 sensor can do flipping in hardware, and then the order in
which it sends out the pixels changes from gbgbgb (for example)
to bgbgbg, for the lines which have blue, effectively changing the
pixelformat, right?
Correct.
In that case I think the only solution is to simply return -EBUSY when
the vflip / hflip controls are changed while a stream is active.
So this effectively forces a reprobe of the hardware?
No, it just disallows changing the flipping (and thus the format) while
an app is actively streaming. so one can use something like v4l2ucp, and
change the flipping while the cam is not being used otherwise, but
if for example skype or cheese or whatever is streaming data from the cam
then the flip will be disallowed (and a device busy error will be returned).
This may not seem very user friendly but normally one does not want to
mess with the flip controls anyways unless the cam is mounted upside down
or something like that.
As for the race window with one application querying the format (or even
setting it) and then another app changing the flip before the application
which just set the format starts the stream, we already have that wrt 2
applications doing this:
app a: setformat x
app b: setformat y
app a: start stream (thinking format is x)
Which is something which normally (luckily) never happens.
If this ever becomes a real issue, shouldn't some kind of user-space
master program aquire the device and then handle format requests for
all client programs?
Yes, one of these days we need to think (very hard) about a much better
way for sharing v4l devices.
Does that sound like a plan ?
Yes, I'll try this ASAP.
Note that this is a solution at the driver level, which IMHO is the only
way as we cannot assume libv4l is always being used.
If it works this sounds like the most clean and elegant solution.
The weak point being that the application must try to renegotiate
the format upon the -EBUSY signal.
No, the idea is that the flipping will simply not change (hence the
error, signaling the setting of the flip control failed).
Regards,
Hans
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