On Sunday 22 February 2009 12:17:58 Hans de Goede wrote: > Hans Verkuil wrote: > >> Cons: Would require polling to support the case of a camera being > >> turned toward / away from the user while streaming. > > > > Polling applies only to the bits that tell the orientation of the > > camera. See below for a discussion of this. > > Didn't we agree to separate orietation (as in sensor mounted upside down) > and the user being able to rotate the camera (which i believe we called > pivotting). Yes, I wrote this more as a clarification since I thought that the original text didn't make this distinction clearly enough. > For the orientation case, which is the case with the sq905X, we do not > need to poll, as for pivotting, here is my proposal: > > Have both orientation and pivotting flags in the input flags. The > pivotting flags will indicate the pivotting state at the moment of doing > the ioctl (which may change later), so these indeed may need to be > polled, unlike the orientation flags which will never change. Ack. I propose to take one of the reserved fields from v4l2_input and either turn it into two __u16 fields (capabilities and flags) or one __u32 field (flags). I'm not sure whether the alignment of two __u16 fields will be done correctly on 32 and 64 bit systems since v4l2_input cannot change in size. Something to test first. > >> Can't easily identify drivers that don't support it. > > > > Not too difficult to add through the use of a capability bit. Either in > > v4l2_input or (perhaps) v4l2_capability. > > +1 > > > Another Pro is that this approach will also work for v4l2_output in the > > case of, say, rotated LCD displays. Using camera orientation bits in > > v4l2_buffer while capturing will work, but using similar bits for > > output will fail since the data is going in the wrong direction. > > > >> The interest in detecting if a driver provides this informnation is to > >> allow libv4l to know when it should use the driver provided > >> information and when it should use its internal table (which needs to > >> be retained for backward compatibility). With no detection capability > >> the driver provided info should be ignored for USB IDs in the built in > >> table. > >> > >> Thoughts please > > > > Is polling bad in this case? It is not something that needs immediate > > attention IMHO. The overhead for checking once every X seconds is > > quite > > > > low. > > Agreed, but it still is something which should be avoided if possible, > implementing polling also means adding a lot of IMHO unneeded code on the > userspace side. > > I would prefer to make the "realtime" pivotting state available to the > app by adding flags containing the pivotting state at frame capture to > the v4l2_buf flags. > > But if people dislike this, libv4l can simple poll the input now and > then. I think this should be prototyped. Compare polling vs. putting the state in the v4l2_buf flags and see if that makes a lot of difference in the user experience compared to polling once a second. If it clearly improves things for the user, then I have no objections to adding bits to v4l2_buf. > > Furthermore, it is only needed on devices that cannot do v/hflipping > > in hardware. > > Erm, no, since we decided we want to differentiate between sensor > orientation and camera pivotting, I think the driver should not > automagically do v/hflipping in the pivot case, this should be left up to > userspace. Maybe the user actually wants to have an upside down picture ? Sorry, you're right. I'd forgotten that. > > An alternative is to put some effort in a proper event interface. There > > is one implemented in include/linux/dvb/video.h and used by ivtv for > > video decoding. The idea is that the application registers events it > > wants to receive, and whenever such an event arrives the select() call > > will exit with a high-prio event (exception). The application then > > checks what happened. > > No not another event interface please. Once could argue that we should > export the pivotting info through the generic linux input system, but not > a v4l specific event interface please. Actually I think making the > pivotting sensor available through the generic input system in addition > to making it available through input flags would be nice to have. Just > like we need to make all those take a picture now buttons on webcams > available through the generic input system. Agreed. I'm not up to date when it comes to the state of event interfaces in linux, and this is a solution for the longer term anyway. I guess someone needs to pick this up and research it to see what works best. Regards, Hans -- Hans Verkuil - video4linux developer - sponsored by TANDBERG -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
