diff options
| -rw-r--r-- | Documentation/guides/application-developer.rst | 40 |
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 --------------------------------- |