libcamera  v0.3.0
Supporting cameras in Linux since 2019
Classes | Public Types | Public Member Functions | List of all members
libcamera::Request Class Reference

A frame capture request. More...

Inheritance diagram for libcamera::Request:
Inheritance graph
Collaboration diagram for libcamera::Request:
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class  Private
 Request private data. More...

Public Types

enum  Status { RequestPending, RequestComplete, RequestCancelled }
enum  ReuseFlag { Default = 0, ReuseBuffers = (1 << 0) }
using BufferMap = std::map< const Stream *, FrameBuffer * >
 A map of Stream to FrameBuffer pointers.

Public Member Functions

 Request (Camera *camera, uint64_t cookie=0)
 Create a capture request for a camera. More...
void reuse (ReuseFlag flags=Default)
 Reset the request for reuse. More...
ControlListcontrols ()
 Retrieve the request's ControlList. More...
ControlListmetadata ()
 Retrieve the request's metadata. More...
const BufferMapbuffers () const
 Retrieve the request's streams to buffers map. More...
int addBuffer (const Stream *stream, FrameBuffer *buffer, std::unique_ptr< Fence > fence=nullptr)
 Add a FrameBuffer with its associated Stream to the Request. More...
FrameBufferfindBuffer (const Stream *stream) const
 Return the buffer associated with a stream. More...
uint32_t sequence () const
 Retrieve the sequence number for the request. More...
uint64_t cookie () const
 Retrieve the cookie set when the request was created. More...
Status status () const
 Retrieve the request completion status. More...
bool hasPendingBuffers () const
 Check if a request has buffers yet to be completed. More...
std::string toString () const
 Generate a string representation of the Request internals. More...
- Public Member Functions inherited from libcamera::Extensible
 Extensible (std::unique_ptr< Private > d)
 Construct an instance of an Extensible class. More...

Additional Inherited Members

- Protected Member Functions inherited from libcamera::Extensible
template<typename T >
const T * _d () const
 Retrieve the private data instance. More...
template<typename T >
T * _d ()
 Retrieve the private data instance. More...

Detailed Description

A frame capture request.

A Request allows an application to associate buffers and controls on a per-frame basis to be queued to the camera device for processing.

Member Enumeration Documentation

◆ ReuseFlag

Flags to control the behavior of Request::reuse()


Don't reuse buffers


Reuse the buffers that were previously added by addBuffer()

◆ Status

Request completion status


The request hasn't completed yet


The request has completed


The request has been cancelled due to capture stop

Constructor & Destructor Documentation

◆ Request()

libcamera::Request::Request ( Camera camera,
uint64_t  cookie = 0 

Create a capture request for a camera.

[in]cameraThe camera that creates the request
[in]cookieOpaque cookie for application use

The cookie is stored in the request and is accessible through the cookie() function at any time. It is typically used by applications to map the request to an external resource in the request completion handler, and is completely opaque to libcamera.

Add a validator for metadata controls.

Member Function Documentation

◆ addBuffer()

int libcamera::Request::addBuffer ( const Stream stream,
FrameBuffer buffer,
std::unique_ptr< Fence fence = nullptr 

Add a FrameBuffer with its associated Stream to the Request.

[in]streamThe stream the buffer belongs to
[in]bufferThe FrameBuffer to add to the request
[in]fenceThe optional fence

A reference to the buffer is stored in the request. The caller is responsible for ensuring that the buffer will remain valid until the request complete callback is called.

A request can only contain one buffer per stream. If a buffer has already been added to the request for the same stream, this function returns -EEXIST.

A Fence can be optionally associated with the buffer.

When a valid Fence is provided to this function, fence is moved to buffer and this Request will only be queued to the device once the fences of all its buffers have been correctly signalled.

If the fence associated with buffer isn't signalled, the request will fail after a timeout. The buffer will still contain the fence, which applications must retrieve with FrameBuffer::releaseFence() before the buffer can be reused in another request. Attempting to add a buffer that still contains a fence to a request will result in this function returning -EEXIST.

See also
0 on success or a negative error code otherwise
Return values
-EEXISTThe request already contains a buffer for the stream or the buffer still references a fence
-EINVALThe buffer does not reference a valid Stream

◆ buffers()

libcamera::Request::buffers ( ) const

Retrieve the request's streams to buffers map.

Return a reference to the map that associates each Stream part of the request to the FrameBuffer the Stream output should be directed to.

The map of Stream to FrameBuffer

◆ controls()

libcamera::Request::controls ( )

Retrieve the request's ControlList.

Requests store a list of controls to be applied to all frames captured for the request. They are created with an empty list of controls that can be accessed through this function. Control values can be retrieved using ControlList::get() and updated using ControlList::set().

Only controls supported by the camera to which this request will be submitted shall be included in the controls list. Attempting to add an unsupported control causes undefined behaviour.

A reference to the ControlList in this request

◆ cookie()

libcamera::Request::cookie ( ) const

Retrieve the cookie set when the request was created.

The request cookie

◆ findBuffer()

FrameBuffer * libcamera::Request::findBuffer ( const Stream stream) const

Return the buffer associated with a stream.

[in]streamThe stream the buffer is associated to
The buffer associated with the stream, or nullptr if the stream is not part of this request

◆ hasPendingBuffers()

bool libcamera::Request::hasPendingBuffers ( ) const

Check if a request has buffers yet to be completed.

True if the request has buffers pending for completion, false otherwise

◆ metadata()

libcamera::Request::metadata ( )

Retrieve the request's metadata.

Offer a read-only API towards applications while keeping a read/write API internally.
The metadata associated with the request

◆ reuse()

void libcamera::Request::reuse ( ReuseFlag  flags = Default)

Reset the request for reuse.

[in]flagsIndicate whether or not to reuse the buffers

Reset the status and controls associated with the request, to allow it to be reused and requeued without destruction. This function shall be called prior to queueing the request to the camera, in lieu of constructing a new request. The application can reuse the buffers that were previously added to the request via addBuffer() by setting flags to ReuseBuffers.

◆ sequence()

uint32_t libcamera::Request::sequence ( ) const

Retrieve the sequence number for the request.

When requests are queued, they are given a sequential number to track the order in which requests are queued to a camera. This number counts all requests given to a camera and is reset to zero between camera stop/start sequences.

It can be used to support debugging and identifying the flow of requests through a pipeline, but does not guarantee to represent the sequence number of any images in the stream. The sequence number is stored as an unsigned integer and will wrap when overflowed.

The request sequence number

◆ status()

libcamera::Request::status ( ) const

Retrieve the request completion status.

The request status indicates whether the request has completed successfully or with an error. When requests are created and before they complete the request status is set to RequestPending, and is updated at completion time to RequestComplete. If a request is cancelled at capture stop before it has completed, its status is set to RequestCancelled.

The request completion status

◆ toString()

std::string libcamera::Request::toString ( ) const

Generate a string representation of the Request internals.

This function facilitates debugging of Request state while it is used internally within libcamera.

A string representing the current state of the request

The documentation for this class was generated from the following files: