Re: qv4l2-bug / libv4lconvert API issue

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 09/26/2012 11:04 PM, Frank Schäfer wrote:
> Hi,
>
> I've noticed the following issues/bugs while playing with qv4l:
> 1.) with pac7302-webcams, only the RGB3 (RGB24) format is working. BGR3,
> YU12 and YV12 are broken
> 2.) for upside-down-mounted devices with an entry in libv4lconvert,
> automatic h/v-flipping doesn't work with some formats
>
> I've been digging a bit deeper into the code and it seems that both
> issues are caused by a problem with the libv4lconvert-API:
> Besides image format conversion, function v4lconvert_convert() also does
> the automatic image flipping and rotation (for devices with flags
> V4LCONTROL_HFLIPPED, V4LCONTROL_VFLIPPED and V4LCONTROL_ROTATED_90_JPEG)
> The problem is, that this function can be called multiple times for the
> same frame, which then of course results in repeated flipping and
> rotation...
>
> And this is exactly what happens with qv4l2:
> qv4l2 gets the frame from libv4l2, which calls v4lconvert_convert() in
> v4l2_dequeue_and_convert() or v4l2_read_and_convert().
> The retrieved frame has the requested format and is already flipped/rotated.
> qv4l2 then calls v4lconvert_convert() again directly to convert the
> frame to RGB24 for GUI-output and this is where things are going wrong.
> In case of h/v-flip, the double conversion "only" equalizes the
> V4LCONTROL_HFLIPPED, V4LCONTROL_VFLIPPED flags, but for rotated devices,
> the image gets corrupted.
>
> Sure, what qv4l2 does is a crazy. Applications usually request the
> format needed for GUI-output directly from libv4l2.
> Anyway, as long as it is valid to call libv4lconvert directly, we can
> not assume that v4lconvert_convert() is called only one time.
>
> At the moment, I see no possibility to fix this without changing the
> libv4lconvert-API.
> Thoughts ?

What you've found is a qv4l2 bug (do you have the latest version?) one
is supposed to either use libv4l2, or do raw device access and then
call libv4lconvert directly. These are also the 2 modes qv4l2 has
(for testing purposes), it is not supposed to do the manual convert call
when using libv4l2 to access the device ...

Regards,

Hans