[libcamera-devel] [RFC PATCH v2 5/9] libcamera: Implement a ControlList

[Kieran Bingham]

Hi Laurent, Niklas,

On 24/06/2019 17:27, Laurent Pinchart wrote:
> Hi Kieran,
> 
> On Mon, Jun 24, 2019 at 04:48:05PM +0100, Kieran Bingham wrote:
>> On 23/06/2019 16:35, Niklas Söderlund wrote:
>>> On 2019-06-21 17:13:57 +0100, Kieran Bingham wrote:
>>>> Define a ControlList which wraps the STL std::unordered_map to contain
>>>> a list of associative pairs of ControlInfo and Value items.
>>>>
>>>> A ControlInfo (or represented by its ControlId) together with a Value
>>>> provide a control item which can be interpreted by the internal IPA and
>>>> PipelineHandler components.
>>>>
>>>> To pass a set of controls around, a ControlList  can be added to a
>>>> Request or stored locally to establish a set of default values for later
>>>> reuse.
>>>>
>>>> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
>>>> ---
>>>>  include/libcamera/controls.h |  41 +++++++++++
>>>>  src/libcamera/controls.cpp   | 128 +++++++++++++++++++++++++++++++++++
>>>>  2 files changed, 169 insertions(+)
>>>>
>>>> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
>>>> index 95198d41c4cf..5835b840a31b 100644
>>>> --- a/include/libcamera/controls.h
>>>> +++ b/include/libcamera/controls.h
>>>> @@ -4,6 +4,9 @@
>>>>   *
>>>>   * controls.h - Control handling
>>>>   */
>>>> +
>>>> +#include <unordered_map>
>>>> +
>>>>  #ifndef __LIBCAMERA_CONTROLS_H__
>>>>  #define __LIBCAMERA_CONTROLS_H__
>>>>  
>>>> @@ -53,6 +56,44 @@ private:
>>>>  
>>>>  std::ostream &operator<<(std::ostream &stream, const ControlInfo &value);
>>>>  
>>>> +class ControlList
>>>> +{
>>>> +private:
>>>> +	struct ControlInfoHasher {
>>>> +		std::size_t operator()(const ControlInfo &ci) const
>>>> +		{
>>>> +			return std::hash<int>()(ci.id());
>>>> +		}
>>>> +	};
>>>> +
>>>> +	typedef std::unordered_map<ControlInfo, Value, ControlInfoHasher> ControlListMap;
>>>
>>> Is this needed to go first or can it be moved down to the other private 
>>> section?
>>
>> It has to be defined before the usages below.
>>
>>>> +
>>>> +public:
>>>> +	ControlList();
>>>> +
>>>> +	using iterator = ControlListMap::iterator;
>>>> +	using const_iterator = ControlListMap::const_iterator;
>>>> +
>>>> +	iterator begin() { return controls_.begin(); }
>>>> +	iterator end() { return controls_.end(); }
>>>> +	const_iterator begin() const { return controls_.begin(); }
>>>> +	const_iterator end() const { return controls_.end(); }
>>>> +
>>>> +	bool contains(ControlId id) const { return controls_.count(id); };
>>>
>>> Would not return controls_.find(id) != controls_.end() be better?
>>
>> I thought this was elegant.
>>
>> Count == 0 = false,
>> count > 0 = true...
> 
> But it's less efficient as it has to go through the whole list in all
> cases.

Hrm... I thought with the guaranteed single key entry, and known hash
algorithm this would be optimised internally : However:

www.cplusplus.com/reference/unordered_map/unordered_map/{count,find}:

Count elements with a specific key
Searches the container for elements whose key is k and returns the
number of elements found. Because unordered_map containers do not allow
for duplicate keys, this means that the function actually returns 1 if
an element with that key exists in the container, and zero otherwise.

But:

Complexity[Count]
Average case: linear in the number of elements counted.
Worst case: linear in container size.

vs

Complexity[Find]
Average case: constant.
Worst case: linear in container size.


Yup... that certainly points to using find();.


>>>> +	bool empty() const { return controls_.empty(); }
>>>> +	size_t size() const { return controls_.size(); }
>>>> +	void reset() { controls_.clear(); }
>>>> +
>>>> +	Value &operator[](ControlId id) { return controls_[id]; }
>>>> +
>>>> +	void update(const ControlList &list);
>>>> +	void update(enum ControlId id, const Value &value);
>>>> +	void update(const ControlInfo &info, const Value &value);
>>>> +
>>>> +private:
>>>> +	ControlListMap controls_;
>>>> +};
>>>> +
>>>>  } /* namespace libcamera */
>>>>  
>>>>  #endif /* __LIBCAMERA_CONTROLS_H__ */
>>>> diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
>>>> index b1be46ddb55e..7c55afffe4ca 100644
>>>> --- a/src/libcamera/controls.cpp
>>>> +++ b/src/libcamera/controls.cpp
>>>> @@ -157,4 +157,132 @@ std::ostream &operator<<(std::ostream &stream, const ControlInfo &info)
>>>>  	return stream << info.toString();
>>>>  }
>>>>  
>>>> +/**
>>>> + * \class ControlList
>>>> + * \brief Associates a list of ControlIds with their values.
>>>> + *
>>>> + * The ControlList stores a pair of ControlInfo and Value classes as an
>>>> + * unordered map. Entries can be updated using array syntax such as
>>>> + *   myControlList[MyControlId] = myValue;
>>>> + * or
>>>> + *   myNewValue = myControlList[MyControlId];
>>>
>>> I don't think this will update the value.
>>
>> No - it updates myNewValue. I'll just remove this. I was trying to put
>> in that the the [] is the accessor.
>>
>>> I think you can drop the examples and the last sentence from the 
>>> documentation.
>>>
>>> With these issues addressed,
>>>
>>> Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>

Thankyou, currently trying to work out if I can drop the whole wrapper
easily though :S

>>>
>>>> + */
>>>> +
>>>> +/**
>>>> + * \brief Construct a ControlList
>>>> + */
>>>> +ControlList::ControlList()
>>>> +{
>>>> +}
>>>> +
>>>> +/**
>>>> + * \typedef ControlList::iterator
>>>> + * \brief Iterator for the controls contained within the list.
>>>> + */
>>>> +
>>>> +/**
>>>> + * \typedef ControlList::const_iterator
>>>> + * \brief Const iterator for the controls contained within the list.
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn iterator ControlList::begin()
>>>> + * \brief Retrieve an iterator to the first Control in the list
>>>> + * \return An iterator to the first Control in the list
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn iterator ControlList::end()
>>>> + * \brief Retrieve an iterator to the next element after the last controls in
>>>> + * the instance.
>>>> + * \return An iterator to the element following the last control in the instance
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn const_iterator ControlList::begin() const
>>>> + * \brief Retrieve a const_iterator to the first Control in the list
>>>> + * \return A const_iterator to the first Control in the list
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn const_iterator ControlList::end() const
>>>> + * \brief Retrieve a constant iterator pointing to an empty element after the
>>>> + * \return A const iterator to the element following the last control in the
>>>> + * instance
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn ControlList::contains()
>>>> + * \brief Identify if the List contains a control with the specified ControlId
>>>> + * \return True if the list contains a matching control, false otherwise
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn ControlList::empty()
>>>> + * \brief Identify if the list is empty
>>>> + * \return True if the list does not contain any control, false otherwise
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn ControlList::size()
>>>> + * \brief Retrieve the number of controls in the list
>>>> + * \return The number of Control entries stored in the list
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn ControlList::reset()
>>>> + * \brief Removes all controls from the list
>>>> + */
>>>> +
>>>> +/**
>>>> + * \fn ControlList::operator[]()
>>>> + * \brief Access the control with the given Id
>>>> + * \param id The id of the control to access
>>>> + * \return The Value of the control with a ControlId of \a Id
>>>> + */
>>>> +
>>>> +/**
>>>> + * \brief Update all Control values with the value from the given \a list
>>>> + * \param list The list of controls to update or append to this list
>>>> + *
>>>> + * Update all controls in the ControlList, by the values given by \a list
>>>> + * If the list already contains a control of this ID then it will be overwritten
>>>> + */
>>>> +void ControlList::update(const ControlList &list)
>>>> +{
>>>> +	for (auto it : list) {
>>>> +		const ControlInfo &info = it.first;
>>>> +		const Value &value = it.second;
>>>> +
>>>> +		controls_[info] = value;
>>>> +	}
>>>> +}
>>>> +
>>>> +/**
>>>> + * \brief Update a control value in the list
>>>> + * \param id The ControlId of the control to update
>>>> + * \param value The new value for the updated control
>>>> + *
>>>> + * Set the Control value in the list to the appropriate value
>>>> + * If the list already contains a control of this ID then it will be overwritten
>>>> + */
>>>> +void ControlList::update(enum ControlId id, const Value &value)
>>>> +{
>>>> +	controls_[id] = value;
>>>> +}
>>>> +
>>>> +/**
>>>> + * \brief Update a control value in the list.
>>>> + * \param info The ControlInfo of the control to update
>>>> + * \param value The new value for the updated control
>>>> + *
>>>> + * Set the Control value in the list to the appropriate value.
>>>> + * If the list already contains a control of the Id matching the ControlInfo
>>>> + * then it will be overwritten.
>>>> + */
>>>> +void ControlList::update(const ControlInfo &info, const Value &value)
>>>> +{
>>>> +	controls_[info] = value;
>>>> +}
>>>> +
>>>>  } /* namespace libcamera */
> 

-- 
Regards
--
Kieran