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diff --git a/Documentation/guides/pipeline-handler.rst b/Documentation/guides/pipeline-handler.rst new file mode 100644 index 00000000..746e2066 --- /dev/null +++ b/Documentation/guides/pipeline-handler.rst @@ -0,0 +1,1473 @@ +.. SPDX-License-Identifier: CC-BY-SA-4.0 + +Pipeline Handler Writers Guide +============================== + +Pipeline handlers are the abstraction layer for device-specific hardware +configuration. They access and control hardware through the V4L2 and Media +Controller kernel interfaces, and implement an internal API to control the ISP +and capture components of a pipeline directly. + +Prerequisite knowledge: system architecture +------------------------------------------- + +A pipeline handler configures and manages the image acquisition and +transformation pipeline realized by specialized system peripherals combined with +an image source connected to the system through a data and control bus. The +presence, number and characteristics of them vary depending on the system design +and the product integration of the target platform. + +System components can be classified in three macro-categories: + +.. TODO: Insert references to the open CSI-2 (and other) specification. + +- Input ports: Interfaces to external devices, usually image sensors, + which transfer data from the physical bus to locations accessible by other + system peripherals. An input port needs to be configured according to the + input image format and size and could optionally apply basic transformations + on the received images, most typically cropping/scaling and some formats + conversion. The industry standard for the system typically targeted by + libcamera is to have receivers compliant with the MIPI CSI-2 specifications, + implemented on a compatible physical layer such as MIPI D-PHY or MIPI C-PHY. + Other design are possible but less common, such as LVDS or the legacy BT.601 + and BT.656 parallel protocols. + +- Image Signal Processor (ISP): A specialized media processor which applies + digital transformations on image streams. ISPs can be integrated as part of + the SoC as a memory interfaced system peripheral or packaged as stand-alone + chips connected to the application processor through a bus. Most hardware used + by libcamera makes use of in-system ISP designs but pipelines can equally + support external ISP chips or be instrumented to use other system resources + such as a GPU or an FPGA IP block. ISPs expose a software programming + interface that allows the configuration of multiple processing blocks which + form an "Image Transformation Pipeline". An ISP usually produces 'processed' + image streams along with the metadata describing the processing steps which + have been applied to generate the output frames. + +- Camera Sensor: Digital components that integrate an image sensor with control + electronics and usually a lens. It interfaces to the SoC image receiver ports + and is programmed to produce images in a format and size suitable for the + current system configuration. Complex camera modules can integrate on-board + ISP or DSP chips and process images before delivering them to the system. Most + systems with a dedicated ISP processor will usually integrate camera sensors + which produce images in Raw Bayer format and defer processing to it. + +It is the responsibility of the pipeline handler to interface with these (and +possibly other) components of the system and implement the following +functionalities: + +- Detect and register camera devices available in the system with an associated + set of image streams. + +- Configure the image acquisition and processing pipeline by assigning the + system resources (memory, shared components, etc.) to satisfy the + configuration requested by the application. + +- Start and the stop the image acquisition and processing sessions. + +- Apply configuration settings requested by applications and computed by image + processing algorithms integrated in libcamera to the hardware devices. + +- Notify applications of the availability of new images and deliver them to the + correct locations. + +Prerequisite knowledge: libcamera architecture +---------------------------------------------- + +A pipeline handler makes use of the following libcamera classes to realize the +functionalities descibed above. Below is a brief overview of each of those: + +.. TODO: (All) Convert to sphinx refs +.. TODO: (MediaDevice) Reference to the Media Device API (possibly with versioning requirements) +.. TODO: (IPAInterface) refer to the IPA guide + +- `MediaDevice <http://libcamera.org/api-html/classlibcamera_1_1MediaDevice.html>`_: + Instances of this class are associated with a kernel media controller + device and its connected objects. + +- `DeviceEnumerator <http://libcamera.org/api-html/classlibcamera_1_1DeviceEnumerator.html>`_: + Enumerates all media devices attached to the system and the media entities + registered with it, by creating instances of the ``MediaDevice`` class and + storing them. + +- `DeviceMatch <http://libcamera.org/api-html/classlibcamera_1_1DeviceMatch.html>`_: + Describes a media device search pattern using entity names, or other + properties. + +- `V4L2VideoDevice <http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html>`_: + Models an instance of a V4L2 video device constructed with the path to a V4L2 + video device node. + +- `V4L2SubDevice <http://libcamera.org/api-html/classlibcamera_1_1V4L2Subdevice.html>`_: + Provides an API to the sub-devices that model the hardware components of a + V4L2 device. + +- `CameraSensor <http://libcamera.org/api-html/classlibcamera_1_1CameraSensor.html>`_: + Abstracts camera sensor handling by hiding the details of the V4L2 subdevice + kernel API and caching sensor information. + +- `CameraData <http://libcamera.org/api-html/classlibcamera_1_1CameraData.html>`_: + Represents device-specific data a pipeline handler associates to each Camera + instance. + +- `StreamConfiguration <http://libcamera.org/api-html/structlibcamera_1_1StreamConfiguration.html>`_: + Models the current configuration of an image stream produced by the camera by + reporting its format and sizes. + +- `CameraConfiguration <http://libcamera.org/api-html/classlibcamera_1_1CameraConfiguration.html>`_: + Represents the current configuration of a camera, which includes a list of + stream configurations for each active stream in a capture session. When + validated, it is applied to the camera. + +- `IPAInterface <http://libcamera.org/api-html/classlibcamera_1_1IPAInterface.html>`_: + The interface to the Image Processing Algorithm (IPA) module which performs + the computation of the image processing pipeline tuning parameters. + +- `ControlList <http://libcamera.org/api-html/classlibcamera_1_1ControlList.html>`_: + A list of control items, indexed by Control<> instances or by numerical index + which contains values used by application and IPA to change parameters of + image streams, used to return to applications and share with IPA the metadata + associated with the captured images, and to advertise the immutable camera + characteristics enumerated at system initialization time. + +Creating a PipelineHandler +-------------------------- + +This guide walks through the steps to create a simple pipeline handler +called “Vivid” that supports the `V4L2 Virtual Video Test Driver`_ (vivid). + +To use the vivid test driver, you first need to check that the vivid kernel +module is loaded, for example with the ``modprobe vivid`` command. + +.. _V4L2 Virtual Video Test Driver: https://www.kernel.org/doc/html/latest/admin-guide/media/vivid.html + +Create the skeleton file structure +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +To add a new pipeline handler, create a directory to hold the pipeline code in +the *src/libcamera/pipeline/* directory that matches the name of the pipeline +(in this case *vivid*). Inside the new directory add a *meson.build* file that +integrates with the libcamera build system, and a *vivid.cpp* file that matches +the name of the pipeline. + +In the *meson.build* file, add the *vivid.cpp* file as a build source for +libcamera by adding it to the global meson ``libcamera_sources`` variable: + +.. code-block:: none + + # SPDX-License-Identifier: CC0-1.0 + + libcamera_sources += files([ + 'vivid.cpp', + ]) + +Users of libcamera can selectively enable pipelines while building libcamera +using the ``pipelines`` option. + +For example, to enable only the IPU3, UVC, and VIVID pipelines, specify them as +a comma separated list with ``-Dpipelines`` when generating a build directory: + +.. code-block:: shell + + meson build -Dpipelines=ipu3,uvcvideo,vivid + +Read the `Meson build configuration`_ documentation for more information on +configuring a build directory. + +.. _Meson build configuration: https://mesonbuild.com/Configuring-a-build-directory.html + +To add the new pipeline handler to this list of options, add its directory name +to the libcamera build options in the top level _meson_options.txt_. + +.. code-block:: none + + option('pipelines', + type : 'array', + choices : ['ipu3', 'raspberrypi', 'rkisp1', 'simple', 'uvcvideo', 'vimc', 'vivid'], + description : 'Select which pipeline handlers to include') + + +In *vivid.cpp* add the pipeline handler to the ``libcamera`` namespace, defining +a `PipelineHandler`_ derived class named PipelineHandlerVivid, and add stub +methods for the overridden class members. + +.. _PipelineHandler: http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html + +.. code-block:: cpp + + namespace libcamera { + + class PipelineHandlerVivid : public PipelineHandler + { + public: + PipelineHandlerVivid(CameraManager *manager); + + CameraConfiguration *generateConfiguration(Camera *camera, + const StreamRoles &roles) override; + int configure(Camera *camera, CameraConfiguration *config) override; + + int exportFrameBuffers(Camera *camera, Stream *stream, + std::vector<std::unique_ptr<FrameBuffer>> *buffers) override; + + int start(Camera *camera) override; + void stop(Camera *camera) override; + + int queueRequestDevice(Camera *camera, Request *request) override; + + bool match(DeviceEnumerator *enumerator) override; + }; + + PipelineHandlerVivid::PipelineHandlerVivid(CameraManager *manager) + : PipelineHandler(manager) + { + } + + CameraConfiguration *PipelineHandlerVivid::generateConfiguration(Camera *camera, + const StreamRoles &roles) + { + return nullptr; + } + + int PipelineHandlerVivid::configure(Camera *camera, CameraConfiguration *config) + { + return -1; + } + + int PipelineHandlerVivid::exportFrameBuffers(Camera *camera, Stream *stream, + std::vector<std::unique_ptr<FrameBuffer>> *buffers) + { + return -1; + } + + int PipelineHandlerVivid::start(Camera *camera) + { + return -1; + } + + void PipelineHandlerVivid::stop(Camera *camera) + { + } + + int PipelineHandlerVivid::queueRequestDevice(Camera *camera, Request *request) + { + return -1; + } + + bool PipelineHandlerVivid::match(DeviceEnumerator *enumerator) + { + return false; + } + + REGISTER_PIPELINE_HANDLER(PipelineHandlerVivid); + + } /* namespace libcamera */ + +Note that you must register the ``PipelineHandler`` subclass with the pipeline +handler factory using the `REGISTER_PIPELINE_HANDLER`_ macro which +registers it and creates a global symbol to reference the class and make it +available to try and match devices. + +.. _REGISTER_PIPELINE_HANDLER: http://libcamera.org/api-html/pipeline__handler_8h.html + +For debugging and testing a pipeline handler during development, you can define +a log message category for the pipeline handler. The ``LOG_DEFINE_CATEGORY`` +macro and ``LIBCAMERA_LOG_LEVELS`` environment variable help you use the inbuilt +libcamera `logging infrastructure`_ that allow for the inspection of internal +operations in a user-configurable way. + +.. _logging infrastructure: http://libcamera.org/api-html/log_8h.html + +Add the following before the ``PipelineHandlerVivid`` class declaration: + +.. code-block:: cpp + + LOG_DEFINE_CATEGORY(VIVID) + +At this point you need the following includes for logging and pipeline handler +features: + +.. code-block:: cpp + + #include "libcamera/internal/log.h" + #include "libcamera/internal/pipeline_handler.h" + +Run the following commands: + +.. code-block:: shell + + meson build + ninja -C build + +To build the libcamera code base, and confirm that the build system found the +new pipeline handler by running: + +.. code-block:: shell + + LIBCAMERA_LOG_LEVELS=Pipeline:0 ./build/src/cam/cam -l + +And you should see output like the below: + +.. code-block:: shell + + DEBUG Pipeline pipeline_handler.cpp:680 Registered pipeline handler "PipelineHandlerVivid" + +Matching devices +~~~~~~~~~~~~~~~~ + +Each pipeline handler registered in libcamera gets tested against the current +system configuration, by matching a ``DeviceMatch`` with the system +``DeviceEnumerator``. A successful match makes sure all the requested components +have been registered in the system and allows the pipeline handler to be +initialized. + +The main entry point of a pipeline handler is the `match()`_ class member +function. When the ``CameraManager`` is started (using the `start()`_ method), +all the registered pipeline handlers are iterated and their ``match`` function +called with an enumerator of all devices it found on a system. + +The match method should identify if there are suitable devices available in the +``DeviceEnumerator`` which the pipeline supports, returning ``true`` if it +matches a device, and ``false`` if it does not. To do this, construct a +`DeviceMatch`_ class with the name of the ``MediaController`` device to match. +You can specify the search further by adding specific media entities to the +search using the ``.add()`` method on the DeviceMatch. + +.. _match(): https://www.libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html#a7cd5b652a2414b543ec20ba9dabf61b6 +.. _start(): http://libcamera.org/api-html/classlibcamera_1_1CameraManager.html#a49e322880a2a26013bb0076788b298c5 +.. _DeviceMatch: http://libcamera.org/api-html/classlibcamera_1_1DeviceMatch.html + +This example uses search patterns that match vivid, but when developing a new +pipeline handler, you should change this value to suit your device identifier. + +Replace the contents of the ``PipelineHandlerVivid::match`` method with the +following: + +.. code-block:: cpp + + DeviceMatch dm("vivid"); + dm.add("vivid-000-vid-cap"); + return false; // Prevent infinite loops for now + +With the device matching criteria defined, attempt to acquire exclusive access +to the matching media controller device with the `acquireMediaDevice`_ method. +If the method attempts to acquire a device it has already matched, it returns +``false``. + +.. _acquireMediaDevice: http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html#a77e424fe704e7b26094164b9189e0f84 + +Add the following below ``dm.add("vivid-000-vid-cap");``: + +.. code-block:: cpp + + MediaDevice *media = acquireMediaDevice(enumerator, dm); + if (!media) + return false; + +The pipeline handler now needs an additional include. Add the following to the +existing include block for device enumeration functionality: + +.. code-block:: cpp + + #include "libcamera/internal/device_enumerator.h" + +At this stage, you should test that the pipeline handler can successfully match +the devices, but have not yet added any code to create a Camera which libcamera +reports to applications. + +As a temporary validation step, add a debug print with + +.. code-block:: cpp + + LOG(VIVID, Debug) << "Vivid Device Identified"; + +before the final closing return statement in the ``PipelineHandlerVivid::match`` +method for when when the pipeline handler successfully matches the +``MediaDevice`` and ``MediaEntity`` names. + +Test that the pipeline handler matches and finds a device by rebuilding, and +running + +.. code-block:: shell + + ninja -C build + LIBCAMERA_LOG_LEVELS=Pipeline,VIVID:0 ./build/src/cam/cam -l + +And you should see output like the below: + +.. code-block:: shell + + DEBUG VIVID vivid.cpp:74 Vivid Device Identified + +Creating camera devices +~~~~~~~~~~~~~~~~~~~~~~~ + +If the pipeline handler successfully matches with the system it is running on, +it can proceed to initialization, by creating all the required instances of the +``V4L2VideoDevice``, ``V4L2Subdevice`` and ``CameraSensor`` hardware abstraction +classes. If the Pipeline handler supports an ISP, it can then also Initialise +the IPA module before proceeding to the creation of the Camera devices. + +An image ``Stream`` represents a sequence of images and data of known size and +format, stored in application-accessible memory locations. Typical examples of +streams are the ISP processed outputs and the raw images captured at the +receivers port output. + +The Pipeline Handler is responsible for defining the set of Streams associated +with the Camera. + +Each Camera has instance-specific data represented using the `CameraData`_ +class, which can be extended for the specific needs of the pipeline handler. + +.. _CameraData: http://libcamera.org/api-html/classlibcamera_1_1CameraData.html + + +To support the Camera we will later register, we need to create a CameraData +class that we can implement for our specific Pipeline Handler. + +Define a new ``VividCameraData()`` class derived from ``CameraData`` by adding +the following code before the PipelineHandlerVivid class definition where it +will be used: + +.. code-block:: cpp + + class VividCameraData : public CameraData + { + public: + VividCameraData(PipelineHandler *pipe, MediaDevice *media) + : CameraData(pipe), media_(media), video_(nullptr) + { + } + + ~VividCameraData() + { + delete video_; + } + + int init(); + void bufferReady(FrameBuffer *buffer); + + MediaDevice *media_; + V4L2VideoDevice *video_; + Stream stream_; + }; + +This example pipeline handler handles a single video device and supports a +single stream, represented by the ``VividCameraData`` class members. More +complex pipeline handlers might register cameras composed of several video +devices and sub-devices, or multiple streams per camera that represent the +several components of the image capture pipeline. You should represent all these +components in the ``CameraData`` derived class when developing a custom +PipelineHandler. + +In our example VividCameraData we implement an ``init()`` function to prepare +the object from our PipelineHandler, however the CameraData class does not +specify the interface for initialisation and PipelineHandlers can manage this +based on their own needs. Derived CameraData classes are used only by their +respective pipeline handlers. + +The CameraData class stores the context required for each camera instance and +is usually responsible for opening all Devices used in the capture pipeline. + +We can now implement the ``init`` method for our example Pipeline Handler to +create a new V4L2 video device from the media entity, which we can specify using +the `MediaDevice::getEntityByName`_ method from the MediaDevice. As our example +is based upon the simplistic Vivid test device, we only need to open a single +capture device named 'vivid-000-vid-cap' by the device. + +.. _MediaDevice::getEntityByName: http://libcamera.org/api-html/classlibcamera_1_1MediaDevice.html#ad5d9279329ef4987ceece2694b33e230 + +.. code-block:: cpp + + int VividCameraData::init() + { + video_ = new V4L2VideoDevice(media_->getEntityByName("vivid-000-vid-cap")); + if (video_->open()) + return -ENODEV; + + return 0; + } + +The CameraData should be created and initialised before we move on to register a +new Camera device so we need to construct and initialise our +VividCameraData after we have identified our device within +PipelineHandlerVivid::match(). The VividCameraData is wrapped by a +std::unique_ptr to help manage the lifetime of our CameraData instance. + +If the camera data initialization fails, return ``false`` to indicate the +failure to the ``match()`` method and prevent retrying of the pipeline handler. + +.. code-block:: cpp + + std::unique_ptr<VividCameraData> data = std::make_unique<VividCameraData>(this, media); + + if (data->init()) + return false; + + +Once the camera data has been initialized, the Camera device instances and the +associated streams have to be registered. Create a set of streams for the +camera, which for this device is only one. You create a camera using the static +`Camera::create`_ method, passing the pipeline handler, the id of the camera, +and the streams available. Then register the camera and its data with the +pipeline handler and camera manager using `registerCamera`_. + +Finally with a successful construction, we return 'true' indicating that the +PipelineHandler successfully matched and constructed a device. + +.. _Camera::create: http://libcamera.org/api-html/classlibcamera_1_1Camera.html#a453740e0d2a2f495048ae307a85a2574 +.. _registerCamera: http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html#adf02a7f1bbd87aca73c0e8d8e0e6c98b + +.. code-block:: cpp + + std::set<Stream *> streams{ &data->stream_ }; + std::shared_ptr<Camera> camera = Camera::create(this, data->video_->deviceName(), streams); + registerCamera(std::move(camera), std::move(data)); + + return true; + + +Our match function should now look like the following: + +.. code-block:: cpp + + bool PipelineHandlerVivid::match(DeviceEnumerator *enumerator) + { + DeviceMatch dm("vivid"); + dm.add("vivid-000-vid-cap"); + + MediaDevice *media = acquireMediaDevice(enumerator, dm); + if (!media) + return false; + + std::unique_ptr<VividCameraData> data = std::make_unique<VividCameraData>(this, media); + + /* Locate and open the capture video node. */ + if (data->init()) + return false; + + /* Create and register the camera. */ + std::set<Stream *> streams{ &data->stream_ }; + std::shared_ptr<Camera> camera = Camera::create(this, data->video_->deviceName(), streams); + registerCamera(std::move(camera), std::move(data)); + + return true; + } + +We will need to use our custom CameraData class frequently throughout the +pipeline handler, so we add a private convenience helper to our Pipeline handler +to obtain and cast the custom CameraData instance from a Camera instance. + +.. code-block:: cpp + + private: + VividCameraData *cameraData(const Camera *camera) + { + return static_cast<VividCameraData *>( + PipelineHandler::cameraData(camera)); + } + +At this point, you need to add the following new includes to provide the Camera +interface, and device interaction interfaces. + +.. code-block:: cpp + + #include <libcamera/camera.h> + #include "libcamera/internal/media_device.h" + #include "libcamera/internal/v4l2_videodevice.h" + +Registering controls and properties +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The libcamera `controls framework`_ allows an application to configure the +streams capture parameters on a per-frame basis and is also used to advertise +immutable properties of the ``Camera`` device. + +The libcamera controls and properties are defined in YAML form which is +processed to automatically generate documentation and interfaces. Controls are +defined by the src/libcamera/`control_ids.yaml`_ file and camera properties +are defined by src/libcamera/`properties_ids.yaml`_. + +.. _controls framework: http://libcamera.org/api-html/controls_8h.html +.. _control_ids.yaml: http://libcamera.org/api-html/control__ids_8h.html +.. _properties_ids.yaml: http://libcamera.org/api-html/property__ids_8h.html + +Pipeline handlers can optionally register the list of controls an application +can set as well as a list of immutable camera properties. Being both +Camera-specific values, they are represented in the ``CameraData`` base class, +which provides two members for this purpose: the `CameraData::controlInfo_`_ and +the `CameraData::properties_`_ fields. + +.. _CameraData::controlInfo_: http://libcamera.org/api-html/classlibcamera_1_1CameraData.html#ab9fecd05c655df6084a2233872144a52 +.. _CameraData::properties_: http://libcamera.org/api-html/classlibcamera_1_1CameraData.html#a84002c29f45bd35566c172bb65e7ec0b + +The ``controlInfo_`` field represents a map of ``ControlId`` instances +associated with the limits of valid values supported for the control. More +information can be found in the `ControlInfoMap`_ class documentation. + +.. _ControlInfoMap: http://libcamera.org/api-html/classlibcamera_1_1ControlInfoMap.html + +Pipeline handlers register controls to expose the tunable device and IPA +parameters to applications. Our example pipeline handler only exposes trivial +controls of the video device, by registering a ``ControlId`` instance with +associated values for each supported V4L2 control but demonstrates the mapping +of V4L2 Controls to libcamera ControlIDs. + +Complete the initialization of the ``VividCameraData`` class by adding the +following code to the ``VividCameraData::init()`` method to initialise the +controls. For more complex control configurations, this could of course be +broken out to a separate function, but for now we just initialise the small set +inline in our CameraData init: + +.. code-block:: cpp + + /* Initialise the supported controls. */ + const ControlInfoMap &controls = video_->controls(); + ControlInfoMap::Map ctrls; + + for (const auto &ctrl : controls) { + const ControlId *id; + ControlInfo info; + + switch (ctrl.first->id()) { + case V4L2_CID_BRIGHTNESS: + id = &controls::Brightness; + info = ControlInfo{ { -1.0f }, { 1.0f }, { 0.0f } }; + break; + case V4L2_CID_CONTRAST: + id = &controls::Contrast; + info = ControlInfo{ { 0.0f }, { 2.0f }, { 1.0f } }; + break; + case V4L2_CID_SATURATION: + id = &controls::Saturation; + info = ControlInfo{ { 0.0f }, { 2.0f }, { 1.0f } }; + break; + default: + continue; + } + + ctrls.emplace(id, info); + } + + controlInfo_ = std::move(ctrls); + +The ``properties_`` field is a list of ``ControlId`` instances +associated with immutable values, which represent static characteristics that can +be used by applications to identify camera devices in the system. Properties can be +registered by inspecting the values of V4L2 controls from the video devices and +camera sensor (for example to retrieve the position and orientation of a camera) +or to express other immutable characteristics. The example pipeline handler does +not register any property, but examples are available in the libcamera code +base. + +.. TODO: Add a property example to the pipeline handler. At least the model. + +At this point you need to add the following includes to the top of the file for +handling controls: + +.. code-block:: cpp + + #include <libcamera/controls.h> + #include <libcamera/control_ids.h> + +Generating a default configuration +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Once ``Camera`` devices and the associated ``Streams`` have been registered, an +application can proceed to acquire and configure the camera to prepare it for a +frame capture session. + +Applications specify the requested configuration by assigning a +``StreamConfiguration`` instance to each stream they want to enable which +expresses the desired image size and pixel format. The stream configurations are +grouped in a ``CameraConfiguration`` which is inspected by the pipeline handler +and validated to adjust it to a supported configuration. This may involve +adjusting the formats or image sizes or alignments for example to match the +capabilities of the device. + +Applications may choose to repeat validation stages, adjusting paramters until a +set of validated StreamConfigurations are returned that is acceptable for the +applications needs. When the pipeline handler receives a valid camera +configuration it can use the image stream configurations to apply settings to +the hardware devices. + +This configuration and validation process is managed with another Pipeline +specific class derived from a common base implementation and interface. + +To support validation in our example pipeline handler, Create a new class called +``VividCameraConfiguration`` derived from the base `CameraConfiguration`_ class +which we can implement and use within our ``PipelineHandlerVivid`` class. + +.. _CameraConfiguration: http://libcamera.org/api-html/classlibcamera_1_1CameraConfiguration.html + +The derived ``CameraConfiguration`` class must override the base class +``validate()`` function, where the stream configuration inspection and +adjustment happens. + +.. code-block:: cpp + + class VividCameraConfiguration : public CameraConfiguration + { + public: + VividCameraConfiguration(); + + Status validate() override; + }; + + VividCameraConfiguration::VividCameraConfiguration() + : CameraConfiguration() + { + } + +Applications generate a ``CameraConfiguration`` instance by calling the +`Camera::generateConfiguration()`_ function, which calls into the pipeline +implementation of the overridden `PipelineHandler::generateConfiguration()`_ +method. + +.. _Camera::generateConfiguration(): http://libcamera.org/api-html/classlibcamera_1_1Camera.html#a25c80eb7fc9b1cf32692ce0c7f09991d +.. _PipelineHandler::generateConfiguration(): http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html#a7932e87735695500ce1f8c7ae449b65b + +Configurations are generated by receiving a list of ``StreamRoles`` instances, +which libcamera uses as predefined ways an application intends to use a camera +(You can read the full list in the `StreamRole API`_ documentation). These are +optional hints on how an application intends to use a stream, and a pipeline +handler should return an ideal configuration for each role that is requested. + +.. _StreamRole API: http://libcamera.org/api-html/stream_8h.html#file_a295d1f5e7828d95c0b0aabc0a8baac03 + +In the pipeline handler ``generateConfiguration`` implementation, remove the +``return nullptr;``, create a new instance of the ``CameraConfiguration`` +derived class, and assign it to a base class pointer. + +.. code-block:: cpp + + VividCameraData *data = cameraData(camera); + CameraConfiguration *config = new VividCameraConfiguration(); + +A ``CameraConfiguration`` is specific to each pipeline, so you can only create +it from the pipeline handler code path. Applications can also generate an empty +configuration and add desired stream configurations manually. Pipelines must +allow for this by returning an empty configuration if no roles are requested. + +To support this in our PipelineHandlerVivid, next add the following check in +``generateConfiguration`` after the Cameraconfiguration has been constructed: + +.. code-block:: cpp + + if (roles.empty()) + return config; + +A production pipeline handler should generate the ``StreamConfiguration`` for +all the appropriate stream roles a camera device supports. For this simpler +example (with only one stream), the pipeline handler always returns the same +configuration, inferred from the underlying V4L2VideoDevice. + +How it does this is shown below, but examination of the more full-featured +pipelines for IPU3, RKISP1 and RaspberryPi are recommend to explore more +complex examples. + +To generate a ``StreamConfiguration``, you need a list of pixel formats and +frame sizes which supported outputs of the stream. You can fetch a map of the +``V4LPixelFormat`` and ``SizeRange`` supported by the underlying output device, +but the pipeline handler needs to convert this to a ``libcamera::PixelFormat`` +type to pass to applications. We do this here using ``std::transform`` to +convert the formats and populate a new ``PixelFormat`` map as shown below. + +Continue adding the following code example to our ``generateConfiguration`` +implementation. + +.. code-block:: cpp + + std::map<V4L2PixelFormat, std::vector<SizeRange>> v4l2Formats = + data->video_->formats(); + std::map<PixelFormat, std::vector<SizeRange>> deviceFormats; + std::transform(v4l2Formats.begin(), v4l2Formats.end(), + std::inserter(deviceFormats, deviceFormats.begin()), + [&](const decltype(v4l2Formats)::value_type &format) { + return decltype(deviceFormats)::value_type{ + format.first.toPixelFormat(), + format.second + }; + }); + +The `StreamFormats`_ class holds information about the pixel formats and frame +sizes that a stream can support. The class groups size information by the pixel +format, which can produce it. + +.. _StreamFormats: http://libcamera.org/api-html/classlibcamera_1_1StreamFormats.html + +The code below uses the ``StreamFormats`` class to represent all of the +supported pixel formats, associated with a list of frame sizes. It then +generates a supported StreamConfiguration to model the information an +application can use to configure a single stream. + +Continue adding the following code to support this: + +.. code-block:: cpp + + StreamFormats formats(deviceFormats); + StreamConfiguration cfg(formats); + +As well as a list of supported StreamFormats, the StreamConfiguration is also +expected to provide an initialsed default configuration. This may be arbitrary, +but depending on use case you may which to select an output that matches the +Sensor output, or prefer a pixelformat which might provide higher performance on +the hardware. The bufferCount represents the number of buffers required to +support functional continuous processing on this stream. + +.. code-block:: cpp + + cfg.pixelFormat = formats::BGR888; + cfg.size = { 1280, 720 }; + cfg.bufferCount = 4; + +Finally add each ``StreamConfiguration`` generated to the +``CameraConfiguration``, and ensure that it has been validated before returning +it to the application. With only a single supported stream, this code adds only +a single StreamConfiguration however a StreamConfiguration should be added for +each supported role in a device that can handle more streams. + +Add the following code to complete the implementation of +``generateConfiguration``: + +.. code-block:: cpp + + config->addConfiguration(cfg); + + config->validate(); + + return config; + +To validate a camera configuration, a pipeline handler must implement the +`CameraConfiguration::validate()`_ method in it's derived class to inspect all +the stream configuration associated to it, make any adjustments required to make +the configuration valid, and return the validation status. + +If changes are made, it marks the configuration as ``Adjusted``, however if the +requested configuration is not supported and cannot be adjusted it shall be +refused and marked as ``Invalid``. + +.. _CameraConfiguration::validate(): http://libcamera.org/api-html/classlibcamera_1_1CameraConfiguration.html#a29f8f263384c6149775b6011c7397093 + +The validation phase makes sure all the platform-specific constraints are +respected by the requested configuration. The most trivial examples being making +sure the requested image formats are supported and the image alignment +restrictions adhered to. The pipeline handler specific implementation of +``validate()`` shall inspect all the configuration parameters received and never +assume they are correct, as applications are free to change the requested stream +parameters after the configuration has been generated. + +Again, this example pipeline handler is simpler, look at the more complex +implementations for a realistic example. + +Add the following function implementation to your file: + +.. code-block:: cpp + + CameraConfiguration::Status VividCameraConfiguration::validate() + { + Status status = Valid; + + if (config_.empty()) + return Invalid; + + if (config_.size() > 1) { + config_.resize(1); + status = Adjusted; + } + + StreamConfiguration &cfg = config_[0]; + + const std::vector<libcamera::PixelFormat> formats = cfg.formats().pixelformats(); + if (std::find(formats.begin(), formats.end(), cfg.pixelFormat) == formats.end()) { + cfg.pixelFormat = cfg.formats().pixelformats()[0]; + LOG(VIVID, Debug) << "Adjusting format to " << cfg.pixelFormat.toString(); + status = Adjusted; + } + + cfg.bufferCount = 4; + + return status; + } + +Now that we are handling the ``PixelFormat`` type, we also need to add +``#include <libcamera/formats.h>`` to the include section before we rebuild the +codebase, and test: + +.. code-block:: shell + + ninja -C build + LIBCAMERA_LOG_LEVELS=Pipeline,VIVID:0 ./build/src/cam/cam -c vivid -I + +You should see the following output showing the capabilites of our new pipeline +handler, and showing that our configurations have been generated: + +.. code-block:: shell + + Using camera vivid + 0: 1280x720-BGR888 + * Pixelformat: NV21 (320x180)-(3840x2160)/(+0,+0) + - 320x180 + - 640x360 + - 640x480 + - 1280x720 + - 1920x1080 + - 3840x2160 + * Pixelformat: NV12 (320x180)-(3840x2160)/(+0,+0) + - 320x180 + - 640x360 + - 640x480 + - 1280x720 + - 1920x1080 + - 3840x2160 + * Pixelformat: BGRA8888 (320x180)-(3840x2160)/(+0,+0) + - 320x180 + - 640x360 + - 640x480 + - 1280x720 + - 1920x1080 + - 3840x2160 + * Pixelformat: RGBA8888 (320x180)-(3840x2160)/(+0,+0) + - 320x180 + - 640x360 + - 640x480 + - 1280x720 + - 1920x1080 + - 3840x2160 + +Configuring a device +~~~~~~~~~~~~~~~~~~~~ + +With the configuration generated, and optionally modified and re-validated, a +pipeline handler needs a method that allows an application to apply a +configuration to the hardware devices. + +The `PipelineHandler::configure()`_ method receives a valid +`CameraConfiguration`_ and applies the settings to hardware devices, using its +parameters to prepare a device for a streaming session with the desired +properties. + +.. _PipelineHandler::configure(): http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html#a930f2a9cdfb51dfb4b9ca3824e84fc29 +.. _CameraConfiguration: http://libcamera.org/api-html/classlibcamera_1_1CameraConfiguration.html + +Replace the contents of the stubbed ``PipelineHandlerVivid::configure`` method +with the following to obtain the camera data and stream configuration. This +pipeline handler supports only a single stream, so it directly obtains the first +``StreamConfiguration`` from the camera configuration. A pipeline handler with +multiple streams should inspect each StreamConfiguration and configure the +system accordingly. + +.. code-block:: cpp + + VividCameraData *data = cameraData(camera); + StreamConfiguration &cfg = config->at(0); + int ret; + +The Vivid capture device is a V4L2 video device, so we use a `V4L2DeviceFormat`_ +with the fourcc and size attributes to apply directly to the capture device +node. The fourcc attribute is a `V4L2PixelFormat`_ and differs from the +``libcamera::PixelFormat``. Converting the format requires knowledge of the +plane configuration for multiplanar formats, so you must explicitly convert it +using the helper ``V4L2VideoDevice::toV4L2PixelFormat()`` provided by the +V4L2VideoDevice instance of which the format will be applied on. + +.. _V4L2DeviceFormat: http://libcamera.org/api-html/classlibcamera_1_1V4L2DeviceFormat.html +.. _V4L2PixelFormat: http://libcamera.org/api-html/classlibcamera_1_1V4L2PixelFormat.html + +Add the following code beneath the code from above: + +.. code-block:: cpp + + V4L2DeviceFormat format = {}; + format.fourcc = data->video_->toV4L2PixelFormat(cfg.pixelFormat); + format.size = cfg.size; + +Set the video device format defined above using the +`V4L2VideoDevice::setFormat()`_ method. You should check if the kernel +driver has adjusted the format, as this shows the pipeline handler has failed to +handle the validation stages correctly, and the configure operation shall also +fail. + +.. _V4L2VideoDevice::setFormat(): http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html#ad67b47dd9327ce5df43350b80c083cca + +Continue the implementation with the following code: + +.. code-block:: cpp + + ret = data->video_->setFormat(&format); + if (ret) + return ret; + + if (format.size != cfg.size || + format.fourcc != data->video_->toV4L2PixelFormat(cfg.pixelFormat)) + return -EINVAL; + +Finally, store and set stream-specific data reflecting the state of the stream. +Associate the configuration with the stream by using the +`StreamConfiguration::setStream`_ method, and set the values of individual +stream configuration members as required. + +.. _StreamConfiguration::setStream: http://libcamera.org/api-html/structlibcamera_1_1StreamConfiguration.html#a74a0eb44dad1b00112c7c0443ae54a12 + +.. NOTE: the cfg.setStream() call here associates the stream to the + StreamConfiguration however that should quite likely be done as part of + the validation process. TBD + +Complete the configure implementation with the following code: + +.. code-block:: cpp + + cfg.setStream(&data->stream_); + cfg.stride = format.planes[0].bpl; + + return 0; + +.. TODO: stride SHALL be assigned in validate + +Initializing device controls +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Pipeline handlers can optionally initialize the video devices and camera sensor +controls at system configuration time, to make sure to make sure they are +defaulted to sane values. Handling of device controls is again performed using +the libcamera `controls framework`_. + +.. _Controls Framework: http://libcamera.org/api-html/controls_8h.html + +This section is particularly specific to Vivid as it sets the initial values of +controls to match `Vivid Controls`_ defined by the kernel driver. You won’t need +any of the code below for your pipeline handler, but it’s included as an example +of how to implement functionality your pipeline handler might need. + +.. _Vivid Controls: https://www.kernel.org/doc/html/latest/admin-guide/media/vivid.html#controls + +We need to add some definitions at the top of the file for convenience. These +come directly from the kernel sources: + +.. code-block:: cpp + + #define VIVID_CID_VIVID_BASE (0x00f00000 | 0xf000) + #define VIVID_CID_VIVID_CLASS (0x00f00000 | 1) + #define VIVID_CID_TEST_PATTERN (VIVID_CID_VIVID_BASE + 0) + #define VIVID_CID_OSD_TEXT_MODE (VIVID_CID_VIVID_BASE + 1) + #define VIVID_CID_HOR_MOVEMENT (VIVID_CID_VIVID_BASE + 2) + +We can now use the V4L2 control IDs to prepare a list of controls with the +`ControlList`_ class, and set them using the `ControlList::set()`_ method. + +.. _ControlList: http://libcamera.org/api-html/classlibcamera_1_1ControlList.html +.. _ControlList::set(): http://libcamera.org/api-html/classlibcamera_1_1ControlList.html#a74a1a29abff5243e6e37ace8e24eb4ba + +In our pipeline ``configure`` method, add the following code after the format +has been set and checked to initialise the ControlList and apply it to the +device: + +.. code-block:: cpp + + ControlList controls(data->video_->controls()); + controls.set(VIVID_CID_TEST_PATTERN, 0); + controls.set(VIVID_CID_OSD_TEXT_MODE, 0); + + controls.set(V4L2_CID_BRIGHTNESS, 128); + controls.set(V4L2_CID_CONTRAST, 128); + controls.set(V4L2_CID_SATURATION, 128); + + controls.set(VIVID_CID_HOR_MOVEMENT, 5); + + ret = data->video_->setControls(&controls); + if (ret) { + LOG(VIVID, Error) << "Failed to set controls: " << ret; + return ret < 0 ? ret : -EINVAL; + } + +These controls configure VIVID to use a default test pattern, and enable all +on-screen display text, while configuring sensible brightness, contrast and +saturation values. Use the ``controls.set`` method to set individual controls. + +Buffer handling and stream control +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Once the system has been configured with the requested parameters, it is now +possible for applications to start capturing frames from the ``Camera`` device. + +libcamera implements a per-frame request capture model, realized by queueing +``Request`` instances to a ``Camera`` object. Before applications can start +submitting capture requests the capture pipeline needs to be prepared to deliver +frames as soon as they are requested. Memory should be initialized and made +available to the devices which have to be started and ready to produce +images. At the end of a capture session the ``Camera`` device needs to be +stopped, to gracefully clean up any allocated memory and stop the hardware +devices. Pipeline handlers implement two methods for these purposes, the +``start()`` and ``stop()`` methods. + +The memory initialization phase that happens at ``start()`` time serves to +configure video devices to be able to use memory buffers exported as dma-buf +file descriptors. From the pipeline handlers perspective the video devices that +provide application facing streams always act as memory importers which use, +in V4L2 terminology, buffers of V4L2_MEMORY_DMABUF memory type. + +libcamera also provides an API to allocate and export memory to applications +realized through the `exportFrameBuffers`_ function and the +`FrameBufferAllocator`_ class which will be presented later. + +.. _exportFrameBuffers: http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html#a6312a69da7129c2ed41f9d9f790adf7c +.. _FrameBufferAllocator: http://libcamera.org/api-html/classlibcamera_1_1FrameBufferAllocator.html + +Please refer to the V4L2VideoDevice API documentation, specifically the +`allocateBuffers`_, `importBuffers`_ and `exportBuffers`_ functions for a +detailed description of the video device memory management. + +.. _allocateBuffers: http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html#a3a1a77e5e6c220ea7878e89485864a1c +.. _importBuffers: http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html#a154f5283d16ebd5e15d63e212745cb64 +.. _exportBuffers: http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html#ae9c0b0a68f350725b63b73a6da5a2ecd + +Video memory buffers are represented in libcamera by the `FrameBuffer`_ class. +A ``FrameBuffer`` instance has to be associated to each ``Stream`` which is part +of a capture ``Request``. Pipeline handlers should prepare the capture devices +by importing the dma-buf file descriptors it needs to operate on. This operation +is performed by using the ``V4L2VideoDevice`` API, which provides an +``importBuffers()`` function that prepares the video device accordingly. + +.. _FrameBuffer: http://libcamera.org/api-html/classlibcamera_1_1FrameBuffer.html + +Implement the pipeline handler ``start()`` function by replacing the stub +version with the following code: + +.. code-block:: c++ + + VividCameraData *data = cameraData(camera); + unsigned int count = data->stream_.configuration().bufferCount; + + int ret = data->video_->importBuffers(count); + if (ret < 0) + return ret; + + return 0; + +During the startup phase pipeline handlers allocate any internal buffer pool +required to transfer data between different components of the image capture +pipeline, for example, between the CSI-2 receiver and the ISP input. The example +pipeline does not require any internal pool, but examples are available in more +complex pipeline handlers in the libcamera code base. + +Applications might want to use memory allocated in the video devices instead of +allocating it from other parts of the system. libcamera provides an abstraction +to assist with this task in the `FrameBufferAllocator`_ class. The +``FrameBufferAllocator`` reserves memory for a ``Stream`` in the video device +and exports it as dma-buf file descriptors. From this point on, the allocated +``FrameBuffer`` are associated to ``Stream`` instances in a ``Request`` and then +imported by the pipeline hander in exactly the same fashion as if they were +allocated elsewhere. + +.. _FrameBufferAllocator: http://libcamera.org/api-html/classlibcamera_1_1FrameBufferAllocator.html + +Pipeline handlers support the ``FrameBufferAllocator`` operations by +implementing the `exportFrameBuffers`_ function, which will allocate memory in +the video device associated with a stream and export it. + +.. _exportFrameBuffers: http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html#a6312a69da7129c2ed41f9d9f790adf7c + +Implement the ``exportFrameBuffers`` stub method with the following code to +handle this: + +.. code-block:: cpp + + unsigned int count = stream->configuration().bufferCount; + VividCameraData *data = cameraData(camera); + + return data->video_->exportBuffers(count, buffers); + +Once memory has been properly setup, the video devices can be started, to +prepare for capture operations. Complete the ``start`` method implementation +with the following code: + +.. code-block:: cpp + + ret = data->video_->streamOn(); + if (ret < 0) { + data->video_->releaseBuffers(); + return ret; + } + + return 0; + +The method starts the video device associated with the stream with the +`streamOn`_ method. If the call fails, the error value is propagated to the +caller and the `releaseBuffers`_ method releases any buffers to leave the device +in a consistent state. If your pipeline handler uses any image processing +algorithms, or other devices you should also stop them. + +.. _streamOn: http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html#a588a5dc9d6f4c54c61136ac43ff9a8cc +.. _releaseBuffers: http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html#a191619c152f764e03bc461611f3fcd35 + +Of course we also need to handle the corresponding actions to stop streaming on +a device, Add the following to the ``stop`` method, to stop the stream with the +`streamOff`_ method and release all buffers. + +.. _streamOff: http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html#a61998710615bdf7aa25a046c8565ed66 + +.. code-block:: cpp + + VividCameraData *data = cameraData(camera); + data->video_->streamOff(); + data->video_->releaseBuffers(); + +Queuing requests between applications and hardware +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +libcamera implements a streaming model based on capture requests queued by an +application to the ``Camera`` device. Each request contains at least one +``Stream`` instance with an associated ``FrameBuffer`` object. + +When an application sends a capture request, the pipeline handler identifies +which video devices have to be provided with buffers to generate a frame from +the enabled streams. + +This example pipeline handler identifies the buffer using the `findBuffer`_ +helper from the only supported stream and queues it to the capture device +directly with the `queueBuffer`_ method provided by the V4L2VideoDevice. + +.. _findBuffer: http://libcamera.org/api-html/classlibcamera_1_1Request.html#ac66050aeb9b92c64218945158559c4d4 +.. _queueBuffer: http://libcamera.org/api-html/classlibcamera_1_1V4L2VideoDevice.html#a594cd594686a8c1cf9ae8dba0b2a8a75 + +Replace the stubbed contents of ``queueRequestDevice`` with the following: + +.. code-block:: cpp + + VividCameraData *data = cameraData(camera); + FrameBuffer *buffer = request->findBuffer(&data->stream_); + if (!buffer) { + LOG(VIVID, Error) + << "Attempt to queue request with invalid stream"; + + return -ENOENT; + } + + int ret = data->video_->queueBuffer(buffer); + if (ret < 0) + return ret; + + return 0; + +Processing controls +~~~~~~~~~~~~~~~~~~~ + +Capture requests not only contain streams and memory buffers, but can +optionally contain a list of controls the application has set to modify the +streaming parameters. + +Applications can set controls registered by the pipeline handler in the +initialization phase, as explained in the `Registering controls and properties`_ +section. + +Implement a ``processControls`` method above the ``queueRequestDevice`` method +to loop through the control list received with each request, and inspect the +control values. Controls may need to be converted between the libcamera control +range definitions and their corresponding values on the device before being set. + +.. code-block:: cpp + + int PipelineHandlerVivid::processControls(VividCameraData *data, Request *request) + { + ControlList controls(data->video_->controls()); + + for (auto it : request->controls()) { + unsigned int id = it.first; + unsigned int offset; + uint32_t cid; + + if (id == controls::Brightness) { + cid = V4L2_CID_BRIGHTNESS; + offset = 128; + } else if (id == controls::Contrast) { + cid = V4L2_CID_CONTRAST; + offset = 0; + } else if (id == controls::Saturation) { + cid = V4L2_CID_SATURATION; + offset = 0; + } else { + continue; + } + + int32_t value = lroundf(it.second.get<float>() * 128 + offset); + controls.set(cid, utils::clamp(value, 0, 255)); + } + + for (const auto &ctrl : controls) + LOG(VIVID, Debug) + << "Setting control " << utils::hex(ctrl.first) + << " to " << ctrl.second.toString(); + + int ret = data->video_->setControls(&controls); + if (ret) { + LOG(VIVID, Error) << "Failed to set controls: " << ret; + return ret < 0 ? ret : -EINVAL; + } + + return ret; + } + +Declare the function prototype for the ``processControls`` method within the +private ``PipelineHandlerVivid`` class members, as it is only used internally as +a helper when processing Requests. + +.. code-block:: cpp + + private: + int processControls(VividCameraData *data, Request *request); + +A pipeline handler is responsible for applying controls provided in a Request to +the relevant hardware devices. This could be directly on the capture device, or +where appropriate by setting controls on V4L2Subdevices directly. Each pipeline +handler is responsible for understanding the correct procedure for applying +controls to the device they support. + +This example pipeline handler applies controls during the `queueRequestDevice`_ +method for each request, and applies them to the capture device through the +capture node. + +.. _queueRequestDevice: http://libcamera.org/api-html/classlibcamera_1_1PipelineHandler.html#a106914cca210640c9da9ee1f0419e83c + +In the ``queueRequestDevice`` method, replace the following: + +.. code-block:: cpp + + int ret = data->video_->queueBuffer(buffer); + if (ret < 0) + return ret; + +With the following code: + +.. code-block:: cpp + + int ret = processControls(data, request); + if (ret < 0) + return ret; + + ret = data->video_->queueBuffer(buffer); + if (ret < 0) + return ret; + +We also need to add the following include directive to support the control +value translation operations: + +.. code-block:: cpp + + #include <math.h> + +Frame completion and event handling +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +libcamera implements a signals and slots mechanism (similar to `Qt Signals and +Slots`_) to connect event sources with callbacks to handle them. + +As a general summary, a ``Slot`` can be connected to a ``Signal``, which when +emitted triggers the execution of the connected slots. A detailed description +of the libcamera implementation is available in the `libcamera Signal and Slot`_ +classes documentation. + +.. _Qt Signals and Slots: https://doc.qt.io/qt-5/signalsandslots.html +.. _libcamera Signal and Slot: http://libcamera.org/api-html/classlibcamera_1_1Signal.html#details + +In order to notify applications about the availability of new frames and data, +the ``Camera`` device exposes two ``Signals`` which applications can connect to +be notified of frame completion events. The ``bufferComplete`` signal serves to +report to applications the completion event of a single ``Stream`` part of a +``Request``, while the ``requestComplete`` signal notifies the completion of all +the ``Streams`` and data submitted as part of a request. This mechanism allows +implementation of partial request completion, which allows an application to +inspect completed buffers associated with the single streams without waiting for +all of them to be ready. + +The ``bufferComplete`` and ``requestComplete`` signals are emitted by the +``Camera`` device upon notifications received from the pipeline handler, which +tracks the buffers and request completion status. + +The single buffer completion notification is implemented by pipeline handlers by +`connecting`_ the ``bufferReady`` signal of the capture devices they have queued +buffers to, to a member function slot that handles processing of the completed +frames. When a buffer is ready, the pipeline handler must propagate the +completion of that buffer to the Camera by using the PipelineHandler base class +``completeBuffer`` function. When all of the buffers referenced by a ``Request`` +have been completed, the pipeline handler must again notify the ``Camera`` using +the PipelineHandler base class ``completeRequest`` function. The PipelineHandler +class implementation makes sure the request completion notifications are +delivered to applications in the same order as they have been submitted. + +.. _connecting: http://libcamera.org/api-html/classlibcamera_1_1Signal.html#aa04db72d5b3091ffbb4920565aeed382 + +Returning to the ``int VividCameraData::init()`` method, add the following above +the closing ``return 0;`` to connects the pipeline handler ``bufferReady`` +method to the V4L2 device buffer signal. + +.. code-block:: cpp + + video_->bufferReady.connect(this, &VividCameraData::bufferReady); + +Create the matching ``VividCameraData::bufferReady`` method after your +VividCameradata::init() impelementation. + +The ``bufferReady`` method obtains the request from the buffer using the +``request`` method, and notifies the ``Camera`` that the buffer and +request are completed. In this simpler pipeline handler, there is only one +stream, so it completes the request immediately. You can find a more complex +example of event handling with supporting multiple streams in the libcamera +code-base. + +.. TODO: Add link + +.. code-block:: cpp + + void VividCameraData::bufferReady(FrameBuffer *buffer) + { + Request *request = buffer->request(); + + pipe_->completeBuffer(camera_, request, buffer); + pipe_->completeRequest(camera_, request); + } + +Testing a pipeline handler +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Once you've built the pipeline handler, we ca rebuild the code base, and test +capture through the pipeline through both of the cam and qcam utilities. + +.. code-block:: shell + + ninja -C build + ./build/src/cam/cam -c vivid -C 5 + +To test that the pipeline handler can detect a device, and capture input. + +Running the command above outputs (a lot of) information about pixel formats, +and then starts capturing frame data, and should provide an output such as the +following: + +.. code-block:: none + + user@dev:/home/libcamera$ ./build/src/cam/cam -c vivid -C5 + [42:34:08.573066847] [186470] INFO IPAManager ipa_manager.cpp:136 libcamera is not installed. Adding '/home/libcamera/build/src/ipa' to the IPA search path + [42:34:08.575908115] [186470] INFO Camera camera_manager.cpp:287 libcamera v0.0.11+876-7b27d262 + [42:34:08.610334268] [186471] INFO IPAProxy ipa_proxy.cpp:122 libcamera is not installed. Loading IPA configuration from '/home/libcamera/src/ipa/vimc/data' + Using camera vivid + [42:34:08.618462130] [186470] WARN V4L2 v4l2_pixelformat.cpp:176 Unsupported V4L2 pixel format Y10 + ... <remaining Unsupported V4L2 pixel format warnings can be ignored> + [42:34:08.619901297] [186470] INFO Camera camera.cpp:793 configuring streams: (0) 1280x720-BGR888 + Capture 5 frames + fps: 0.00 stream0 seq: 000000 bytesused: 2764800 + fps: 4.98 stream0 seq: 000001 bytesused: 2764800 + fps: 5.00 stream0 seq: 000002 bytesused: 2764800 + fps: 5.03 stream0 seq: 000003 bytesused: 2764800 + fps: 5.03 stream0 seq: 000004 bytesused: 2764800 + +This demonstrates that the pipeline handler is successfully capturing frames, +but it is helpful to see the visual output and validate the images are being +processed correctly. The libcamera project also implements a Qt based +application which will render the frames in a window for visual inspection: + +.. code-block:: shell + + ./build/src/qcam/qcam -c vivid + +.. TODO: Running qcam with the vivid pipeline handler appears to have a bug and + no visual frames are seen. However disabling zero-copy on qcam renders + them successfully.
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