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authorDaniel Semkowicz <dse@thaumatec.com>2022-06-17 16:35:49 +0200
committerLaurent Pinchart <laurent.pinchart@ideasonboard.com>2022-06-17 18:08:55 +0300
commitd2c097c4828e15821b6d14b101f2d627f2371c39 (patch)
tree6d9be1bcbbed1601283ea1a5cb2996bc288bb37f /Documentation/guides/application-developer.rst
parentd85a91cf56a68cea30019362f1206dcebce3db23 (diff)
Documentation: Update the "Start an event loop" section
Event loop was moved to be a part of CameraManager, so it is no longer a user responsibility to control the event dispatching. Signed-off-by: Daniel Semkowicz <dse@thaumatec.com> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Diffstat (limited to 'Documentation/guides/application-developer.rst')
-rw-r--r--Documentation/guides/application-developer.rst40
1 files changed, 17 insertions, 23 deletions
diff --git a/Documentation/guides/application-developer.rst b/Documentation/guides/application-developer.rst
index b97047cd..1b2d7727 100644
--- a/Documentation/guides/application-developer.rst
+++ b/Documentation/guides/application-developer.rst
@@ -27,10 +27,12 @@ defined names and types without the need of prefixing them.
#include <iomanip>
#include <iostream>
#include <memory>
+ #include <thread>
#include <libcamera/libcamera.h>
using namespace libcamera;
+ using namespace std::chrono_literals;
int main()
{
@@ -506,35 +508,27 @@ and queue all the previously created requests.
for (std::unique_ptr<Request> &request : requests)
camera->queueRequest(request.get());
-Start an event loop
-~~~~~~~~~~~~~~~~~~~
+Event processing
+~~~~~~~~~~~~~~~~
-The libcamera library needs an event loop to monitor and dispatch events
-generated by the video devices part of the capture pipeline. libcamera provides
-its own ``EventDispatcher`` class (inspired by the `Qt event system`_) to
-process and deliver events generated by ``EventNotifiers``.
+libcamera creates an internal execution thread at `CameraManager::start()`_
+time to decouple its own event processing from the application's main thread.
+Applications are thus free to manage their own execution opportunely, and only
+need to respond to events generated by libcamera emitted through signals.
-.. _Qt event system: https://doc.qt.io/qt-5/eventsandfilters.html
+.. _CameraManager::start(): https://libcamera.org/api-html/classlibcamera_1_1CameraManager.html#a49e322880a2a26013bb0076788b298c5
-The libcamera library implements this by creating instances of the
-``EventNotifier`` class, which models a file descriptor event source registered
-to an ``EventDispatcher``. Whenever the ``EventDispatcher`` detects an event on
-a notifier it is monitoring, it emits the notifier's
-``EventNotifier::activated`` signal. The libcamera components connect to the
-notifiers' signals and emit application visible events, such as the
-``Camera::bufferReady`` and ``Camera::requestCompleted`` signals.
-
-The code below retrieves a reference to the system-wide event dispatcher and for
-the a fixed duration of 3 seconds, processes all the events detected in the
-system.
+Real-world applications will likely either integrate with the event loop of the
+framework they use, or create their own event loop to respond to user events.
+For the simple application presented in this example, it is enough to prevent
+immediate termination by pausing for 3 seconds. During that time, the libcamera
+thread will generate request completion events that the application will handle
+in the ``requestComplete()`` slot connected to the ``Camera::requestCompleted``
+signal.
.. code:: cpp
- EventDispatcher *dispatcher = cm->eventDispatcher();
- Timer timer;
- timer.start(3000);
- while (timer.isRunning())
- dispatcher->processEvents();
+ std::this_thread::sleep_for(3000ms);
Clean up and stop the application
---------------------------------