[PATCH v1 2/4] libcamera: controls: Strings are arrays

[Barnabás Pőcze]

Hi


2025. 04. 01. 23:43 keltezéssel, Laurent Pinchart írta:
> Hi Barnabás,
> 
> Thank you for the patch.
> 
> On Tue, Apr 01, 2025 at 03:19:37PM +0200, Barnabás Pőcze wrote:
>> `ControlId::isArray()` and `ControlValue::isArray()` disagree
>> in the case of strings.
> 
> I think that's on purpose, or at least partly. ControlValue::isArray()
> is used to indicate that the value is stored as an array of characters,
> while ControlId::isArray() indicates whether the control has a single or
> multiple values. The clash in naming is unfortunate, but strings are a
> hybrid beast.

This inconsistency is nonetheless quite unfortunate, it makes it hard to
handle control values in a reasonably uniform way because strings need
special handling somewhere.


Regards,
Barnabás Pőcze


> 
>> Fix it by setting the static size of a
>> string to `libcamera::dynamic_extent` to denote a dynamically
>> sized array-like value.
>>
>> One unfortunate side effect of this change is that if there were
>> string controls (there are none at the moment), then `cam` would
>> display them with an extra `Size: n` annotation.
>>
>> Bug: https://bugs.libcamera.org/show_bug.cgi?id=255
>> Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>
>> ---
>>   include/libcamera/controls.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
>> index c1919d864..d35347f4c 100644
>> --- a/include/libcamera/controls.h
>> +++ b/include/libcamera/controls.h
>> @@ -98,7 +98,7 @@ struct control_type<float> {
>>   template<>
>>   struct control_type<std::string> {
>>   	static constexpr ControlType value = ControlTypeString;
>> -	static constexpr std::size_t size = 0;
>> +	static constexpr std::size_t size = libcamera::dynamic_extent;
>>   };
>>   
>>   template<>
>