On Mon January 7 2013 11:46:38 Andrzej Hajda wrote: > Hi, > > I have included this proposition already in the post "[PATCH RFC 0/2] > V4L: Add auto focus area control and selection" but it left unanswered. > I repost it again in a separate e-mail, I hope this way it will be > easier to attract attention. > > Problem description > > 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. Regards, Hans > > I have presented all three cases to show the advantages of this solution: > - atomicity - control and its parameters are passed in one call, > - flexibility - we are not limited by a fixed number of parameters, > - no-redundancy - we can pass only required parameters > (no need to pass null width and height in case of spot selection), > - extensibility - it is possible to extend parameters in the future, > for example add parameters to V4L2_AUTO_FOCUS_AREA_OBJECT_DETECTION, > without breaking API, > - backward compatibility, > - re-usability - this schema could be used in other controls, > pseudo-controls could be re-used in other controls as well. > - API backward compatibility. > > > Regards > Andrzej Hajda > -- > 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 > -- 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
