[libcamera-devel] Compound libcamera controls?

[Jacopo Mondi]

Hi Naush,

On Tue, Jun 09, 2020 at 09:42:59AM +0100, Naushir Patuck wrote:
> Hi,
>
> I've been looking to add some controls related to returning out focus
> statistics via libcamera controls.  The simplest way to do this would
> be to return a single numeric value to indicate the "sharpness" or
> "contrast" of the image.
>
> However, I got thinking a bit more and ideally, we would like to
> return a numeric metric for a number of zones or regions around the
> image.  Of course, these zones could be setup by the user, so there
> needs to be a libcamera control to setup regions.  One way to do this
> would be to have another libcamera control to set a list of focus
> regions.  However, as we know, libcamera controls only accept either
> singular values or arrays, and that could be cumbersome for specifying
> regions.  Ideally, we would want to specify a region as a struct with
> {x, y, width, height}, and have the control accept an array of these
> structs, together with the number of regions to be used.
>
> Is there any plans to extend libcamera::controls to allow compound
> types for such use cases.  If no, any suggestions what the most
> convenient way to specify a number of zones would be?

You can do so today, if I got your request right.

You can declare a control to have type 'Rectangle' (x, y,
width, height) and assign it a 'size' (just adding the size property
to the control yaml definition makes it a compound control).

we don't have example of this in mainline libcamera, but have a look
at some properties patches on the list, like
"[PATCH v6] libcamera: properties: Define pixel array properties"

You'll there find, in example:

+  - PixelArrayOpticalBlackRectangles:
+      type: Rectangle
+      size: [1 x n]
+      description: |

Would you be able to handle your use case with this ? Also please note
that you can easily access the number of entries in the control with
ControlValue::numElements(), so there's no need to pass that as an
additional argument to the control.

Thanks
  j


>
> Regards,
> Naush
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