[RFC,v3,17/22] guides: pipeline_handler: Document PipelineHandler::metadataAvailable
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Message ID 20251030165816.1095180-18-barnabas.pocze@ideasonboard.com
State New
Headers show
Series
  • libcamera: Add `MetadataList`
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Commit Message

Barnabás Pőcze Oct. 30, 2025, 4:58 p.m. UTC
From: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

Document the new available helpers to accumulate metadata results in
Request::metadata and notify applications about metadata availability.

Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
---
Original: https://patchwork.libcamera.org/patch/22230/

changes in v3:
  * reword some parts
---
 Documentation/guides/pipeline-handler.rst | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

Patch
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diff --git a/Documentation/guides/pipeline-handler.rst b/Documentation/guides/pipeline-handler.rst
index 85d9cc8700..9ec0da01b9 100644
--- a/Documentation/guides/pipeline-handler.rst
+++ b/Documentation/guides/pipeline-handler.rst
@@ -1358,18 +1358,27 @@  and Slot <Signal>` classes documentation.
 .. _Qt Signals and Slots: https://doc.qt.io/qt-6/signalsandslots.html
 
 In order to notify applications about the availability of new frames and data,
-the ``Camera`` device exposes two ``Signals`` to 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
+the ``Camera`` device exposes three ``Signals`` to which applications can
+connect to be notified of frame completion and metadata availability events.
+
+The ``metadataAvailable`` signal serves to notify about the availability of
+metadata for a particular ``Request``. 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 ``metadataAvailable``, ``bufferComplete`` and ``requestComplete`` signals
+are emitted by the ``Camera`` device upon notifications received from the
+pipeline handler, which tracks the metadata, buffers and request completion
+status.
+
+Metadata availability is signalled by the pipeline handlers by calling the
+PipelineHandler base class ``metadataAvailable`` function. This function
+notifies applications about metadata availability and accumulates metadata
+results in the ``Request::metadata()`` list.
 
 The single buffer completion notification is implemented by pipeline handlers
 by :doxy-int:`connecting <Signal::connect>` the ``bufferReady`` signal of the