Hi Sylwester, On Thursday 31 January 2013 18:17:42 Sylwester Nawrocki wrote: > On 01/07/2013 01:10 PM, Hans Verkuil wrote: > > On Mon January 7 2013 11:46:38 Andrzej Hajda wrote: > [...] > > >> Currently V4L2 controls can have only single value (of type int, int64, > >> string). Some hardware controls require more than single int parameter, > >> for example to set auto-focus (AF) rectangle four coordinates should be > >> passed, to set auto-focus spot two coordinates should be passed. > >> > >> Current solution > >> > >> In case of AF rectangle we can reuse selection API as in "[PATCH RFC > >> 0/2] V4L: Add auto focus area control and selection" post. > >> Pros: > >> - reuse existing API, > >> Cons: > >> - two IOCTL's to perform one action, > >> - non-atomic operation, > >> - fits well only for rectangles and spots (but with unused fields width, > >> height), in case of other parameters we should find a different way. > >> > >> Proposed solution > >> > >> The solution takes an advantage of the fact VIDIOC_(G/S/TRY)_EXT_CTRLS > >> ioctls can be called with multiple controls per call. > >> > >> I will present it using AF area control example. > >> > >> There could be added four pseudo-controls, lets call them for short: > >> LEFT, TOP, WIDTH, HEIGHT. Those controls could be passed together with > >> V4L2_AUTO_FOCUS_AREA_RECTANGLE control in one ioctl as a kind of > >> parameters. > >> > >> For example setting auto-focus spot would require calling > >> VIDIOC_S_EXT_CTRLS with the following controls: > >> - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_RECTANGLE > >> - LEFT = ... > >> - RIGHT = ... > >> > >> Setting AF rectangle: > >> - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_RECTANGLE > >> - LEFT = ... > >> - TOP = ... > >> - WIDTH = ... > >> - HEIGHT = ... > >> > >> Setting AF object detection (no parameters required): > >> - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_OBJECT_DETECTION > > > > If you want to do this, then you have to make LEFT/TOP/WIDTH/HEIGHT real > > controls. There is no such thing as a pseudo control. So you need five > > new controls in total: > > > > V4L2_CID_AUTO_FOCUS_AREA > > V4L2_CID_AUTO_FOCUS_LEFT > > V4L2_CID_AUTO_FOCUS_RIGHT > > V4L2_CID_AUTO_FOCUS_WIDTH > > V4L2_CID_AUTO_FOCUS_HEIGHT > > > > I have no problem with this from the point of view of the control API, but > > whether this is the best solution for implementing auto-focus is a > > different issue and input from sensor specialists is needed as well > > (added Laurent and Sakari to the CC list). > > > > The primary concern I have is that this does not scale to multiple focus > > rectangles. This might not be relevant to auto focus, though. > > I think for more advanced hardware/configurations there is a need to > associate more information with the rectangles anyway. So the selections > API seems too limited. Probably a new IOCTL would be needed for that, > either standard or private. > > We've discussed it here with Andrzej and using such 4 controls to specify > the AF rectangle looks sufficient from our POV. > > I would just probably rename LEFT/RIGHT to POS_X/POS_Y or something, > as these 2 controls could be used in a focus mode where only spot > position needs to be specified. If position and size are sufficient, could we use the selection API instead ? An alternative would be to introduce rectangle controls. I'm a bit uncomfortable with using 4 controls here, as this could quickly grow out of control. -- Regards, Laurent Pinchart -- 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
