[PATCH v2] libcamera: controls: Add overwriteExisting parameter to ControlList::merge

[Laurent Pinchart]

Hi Stefan,

Thank you for the patch.

On Mon, Mar 04, 2024 at 04:58:53PM +0100, Stefan Klug wrote:
> This is useful in many cases although not included in the stl.
> 
> Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
> ---
> 
> This version adds a unittest and fixes a doxygen doc.
> 
>  include/libcamera/controls.h   |  2 +-
>  src/libcamera/controls.cpp     |  9 ++++--
>  test/controls/control_list.cpp | 50 ++++++++++++++++++++++++++++++++++
>  3 files changed, 57 insertions(+), 4 deletions(-)
> 
> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
> index cf942055..0bf778d8 100644
> --- a/include/libcamera/controls.h
> +++ b/include/libcamera/controls.h
> @@ -368,7 +368,7 @@ public:
>  	std::size_t size() const { return controls_.size(); }
>  
>  	void clear() { controls_.clear(); }
> -	void merge(const ControlList &source);
> +	void merge(const ControlList &source, bool overwriteExisting = false);

The way to implement a.merge(b, true) with C++ STL would be

	b.merge(a);
	b.swap(a);

I understand this is not ideal though, and that a nicer API would be,
well, nicer. I am however concerned with the bool flag, as it isn't very
readable. Consider the following code:

	a.merge(b);
	a.merge(b, false);
	a.merge(b, true);

Readers can't easily tell what happens. An alternative would be to use
an enum.

class ControList
{
	...

	enum class MergePolicy {
		Ignore,
		Overwrite,
	};

	void merge(const ControlList &source,
		   MergePolicy policy = MergePolicy::Ignore);

	...
};

(bikeshedding on the names is allowed)

With that, reading

	a.merge(b);
	a.merge(b, ControlList::MergePolicy::Ignore);
	a.merge(b, ControlList::MergePolicy::Overwrite);

becomes clearer. You still can't tell what the default is (that's the
trouble with default parameters), but the second and third line are much
more explicit.

>  
>  	bool contains(unsigned int id) const;
>  
> diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
> index b808116c..93ce4efe 100644
> --- a/src/libcamera/controls.cpp
> +++ b/src/libcamera/controls.cpp
> @@ -910,10 +910,13 @@ ControlList::ControlList(const ControlInfoMap &infoMap,
>  /**
>   * \brief Merge the \a source into the ControlList
>   * \param[in] source The ControlList to merge into this object
> + * \param[in] overwriteExisting Control if existing elements in *this shall be
> + * overwritten
>   *
>   * Merging two control lists copies elements from the \a source and inserts
>   * them in *this. If the \a source contains elements whose key is already
> - * present in *this, then those elements are not overwritten.
> + * present in *this, then those elements are only overwritten if
> + * \a overwriteExisting is true.
>   *
>   * Only control lists created from the same ControlIdMap or ControlInfoMap may
>   * be merged. Attempting to do otherwise results in undefined behaviour.
> @@ -921,7 +924,7 @@ ControlList::ControlList(const ControlInfoMap &infoMap,
>   * \todo Reimplement or implement an overloaded version which internally uses
>   * std::unordered_map::merge() and accepts a non-const argument.
>   */
> -void ControlList::merge(const ControlList &source)
> +void ControlList::merge(const ControlList &source, bool overwriteExisting)
>  {
>  	/**
>  	 * \todo ASSERT that the current and source ControlList are derived
> @@ -936,7 +939,7 @@ void ControlList::merge(const ControlList &source)
>  	 */
>  
>  	for (const auto &ctrl : source) {
> -		if (contains(ctrl.first)) {
> +		if (!overwriteExisting && contains(ctrl.first)) {
>  			const ControlId *id = idmap_->at(ctrl.first);
>  			LOG(Controls, Warning)
>  				<< "Control " << id->name() << " not overwritten";
> diff --git a/test/controls/control_list.cpp b/test/controls/control_list.cpp
> index c03f230e..304cabfc 100644
> --- a/test/controls/control_list.cpp
> +++ b/test/controls/control_list.cpp
> @@ -196,6 +196,56 @@ protected:
>  			return TestFail;
>  		}
>  
> +		/*
> +		 * Create two lists with overlapping controls. Merge them with
> +		 * overwriteExisting = true, verifying that the existing control
> +		 * values *get* overwritten.
> +		 */
> +		mergeList.clear();
> +		mergeList.set(controls::Brightness, 0.7f);
> +		mergeList.set(controls::Saturation, 0.4f);
> +
> +		list.clear();
> +		list.set(controls::Brightness, 0.5f);
> +		list.set(controls::Contrast, 1.1f);
> +
> +		mergeList.merge(list, true);
> +		if (mergeList.size() != 3) {
> +			cout << "Merged list should contain three elements" << endl;
> +			return TestFail;
> +		}
> +
> +		if (list.size() != 2) {
> +			cout << "The list to merge should contain two elements"
> +			     << endl;
> +			return TestFail;
> +		}
> +
> +		if (!mergeList.get(controls::Brightness) ||
> +		    !mergeList.get(controls::Contrast) ||
> +		    !mergeList.get(controls::Saturation)) {
> +			cout << "Merged list does not contain all controls" << endl;
> +			return TestFail;
> +		}
> +
> +		if (mergeList.get(controls::Brightness) != 0.5f) {
> +			cout << "Brightness control value did not change after merging lists"
> +			     << endl;
> +			return TestFail;
> +		}
> +
> +		if (mergeList.get(controls::Contrast) != 1.1f) {
> +			cout << "Contrast control value did not change after merging lists"
> +			     << endl;
> +			return TestFail;
> +		}
> +
> +		if (mergeList.get(controls::Saturation) != 0.4f) {
> +			cout << "Saturation control value changed after merging lists"
> +			     << endl;
> +			return TestFail;
> +		}
> +
>  		return TestPass;
>  	}
>  };

-- 
Regards,

Laurent Pinchart