Part 11 (C++ GUI)

In this section, we’ll build a very simple user interface for talking to your pipeline. Building a C++ GUI is very similar to building a pipeline, but with slightly different nomenclature and rules.

Let’s start by editing ${APP_ROOT}/tutorial/gui/tutorial_gui.cc:

#include "ark/gui/gui_application.hh"

#include "ark/config/gui/config_package_plugin.hh"
#include "ark/debuglog/gui/debug_logger_plugin.hh"
#include "ark/logging/gui/log_writer_plugin.hh"
#include "ark/perf/gui/tracer_plugin.hh"
#include "ark/pipeline/gui/pipeline_metrics_plugin.hh"
#include "ark/plotting/gui/json_decoder_plugin.hh"
#include "ark/plotting/gui/plotting_host_plugin.hh"

int main(int argc, const char **argv)
{
    ark::gui::GuiApplicationConfig app_config;
    app_config.name = "Tutorial GUI";

    ark::gui::GuiApplication application(std::move(app_config), argc, argv);

    application.register_central_plugin<ark::config::ConfigPackagePlugin>();
    application.register_central_plugin<ark::perf::TracerPlugin>();
    application.register_central_plugin<ark::pipeline::PipelineMetricsPlugin>();
    application.register_central_plugin<ark::plotting::PlottingHostPlugin>();

    application.register_bottom_plugin<ark::debuglog::DebugLoggerPlugin>();

    application.register_right_plugin<ark::logging::LogWriterPlugin>();
    application.register_right_plugin<ark::plotting::JsonDecoderPlugin>();

    return application.execute();
}

This is adding a bit more then we did before. It adds seven plugins in total. Four of them will be in a central pane, one will be at the bottom, and two will be on the right hand side of the GUI.

These are just a few prebuilt Ark plugins to help you inspect pipelines. Most developer GUIs will have these plugins.

Let’s edit the ${APP_ROOT}/tutorial/gui/CMakeLists.txt file to add the GUI:

qt_add_resources(resources_source ${QDARKSTYLE_RESOURCE})
add_library(tutorial_resources ${resources_source})

add_executable(tutorial_gui tutorial_gui.cc)

target_link_libraries(
    tutorial_gui
    PRIVATE ark::gui
            ark::config_package_plugin
            ark::debug_logger_plugin
            ark::tracer_plugin
            ark::log_writer_plugin
            ark::pipeline_metrics_plugin
            ark::plotting_host_plugin
            ark::json_decoder_plugin
            -Wl,--whole-archive
            tutorial_resources
            -Wl,--no-whole-archive)

And finally, edit the top-level CMakeLists.txt file, and add this line:

build_qt_gui(tutorial/gui)

We use build_qt_gui here instead of add_subdirectory to ensure that we don’t build GUI components on platforms/systems that do not support building GUI components.

Building should proceed without error, and you should then run your tutorial_pipeline in one terminal, then run the GUI in a new terminal with:

./build/tutorial_gui

It should open a window, and look something like this:

From here, you should be able to do things like see profiling metrics, plot variables, view JSON versions of messages, or start/stop logging.

Pipeline Metrics

You’ll notice the “Pipeline Metrics” tab is empty. This is because we aren’t sending them yet! If you want to see them, let’s update your tutorial_pipeline.cc file once again, and add this line to your MainOffboardConfiguration:

config.add_pipeline_metrics_stage = true;

Rebuild and re-run your pipeline. Your GUI will automatically reconnect, and you should now see pipeline metrics populated. This tells you how many messages your stages are sending, among other things:

From here, you can see the three stages that we built, and notice that they are emitting and receiving messages at the expected rates.

Continue to Part 12.