fix: QDS-11873 laggy QR scanner

CMakeLists.txt

@@ -13,13 +13,13 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 find_package(
     QT NAMES Qt6
-    COMPONENTS Core
+    COMPONENTS Core Widgets Quick Gui Qml Multimedia MultimediaWidgets Concurrent
     REQUIRED
 )
 
 find_package(
     Qt6
-    COMPONENTS Core Widgets Quick Gui Qml Multimedia MultimediaWidgets
+    COMPONENTS Core Widgets Quick Gui Qml Multimedia MultimediaWidgets Concurrent
     REQUIRED
 )
 
@@ -44,9 +44,11 @@ qt_add_executable(${PROJECT_NAME}
 )
 
 target_link_libraries(${PROJECT_NAME} PRIVATE
-    Qt::Core Qt::Widgets
-    Qt::Quick Qt::Gui
-    Qt::Qml Qt::GuiPrivate Qt::Multimedia Qt::MultimediaWidgets
+    Qt6::Core Qt6::Widgets
+    Qt6::Quick Qt6::Gui
+    Qt6::Qml Qt6::GuiPrivate
+    Qt6::Multimedia Qt6::MultimediaWidgets
+    Qt6::Concurrent
     ZXing::ZXing
 )
 

src/backend.cpp

@@ -28,6 +28,7 @@
 
 #include <QCameraDevice>
 #include <QDesktopServices>
+#include <QElapsedTimer>
 #include <QFileInfo>
 #include <QJsonArray>
 #include <QJsonObject>
@@ -37,6 +38,7 @@
 #include <QSettings>
 #include <QSslSocket>
 #include <QVideoSink>
+#include <QtConcurrent>
 
 #include "../3rdparty/zxing-cpp/example/ZXingQtReader.h"
 
@@ -217,20 +219,47 @@ void Backend::openCamera()
             this,
             [&](const QVideoFrame &frame) {
                 static int i = 0;
-                if (i++ < 30) {
+                static QAtomicInt running = 0;
+
+                if (i++ < 20 || running > 0) {
                     return;
                 }
 
                 i = 0;
 
-                auto results = ReadBarcodes(frame.toImage());
-                for (auto &result : results) {
+                QtConcurrent::run([=] {
+                    // lock the thread so that only one barcode can be read at a time
+                    running++;
+
+                    QElapsedTimer timer;
+                    timer.start();
+                    QList<Result> results = ReadBarcodes(frame.toImage());
+                    qDebug() << "Barcode detection took" << timer.elapsed() << "ms";
+
+                    // release the lock so that another barcode can be read
+                    running--;
+                    return results;
+                }).then([=](const QList<Result> &results) {
+                    if (results.isEmpty() || !m_captureSession)
+                        return;
+
+                    qDebug() << "Stopping camera";
+                    qobject_cast<CustomVideoWidget *>(m_captureSession->videoOutput())->close();
+                    qDebug() << "Camera stopped";
+
+                    Result result = results.first();
+
                     qDebug() << "Text:   " << result.text();
                     qDebug() << "Format: " << result.format();
                     qDebug() << "Content:" << result.contentType();
-                    parseDesignViewerUrl(result.text());
-                    qobject_cast<CustomVideoWidget *>(m_captureSession->videoOutput())->close();
-                }
+
+                    // we have to use invokeMethod because we are in a different thread
+                    // then where the serviceConnector is created
+                    QMetaObject::invokeMethod(this,
+                                              "parseDesignViewerUrl",
+                                              Qt::QueuedConnection,
+                                              Q_ARG(QUrl, result.text()));
+                });
             });
 
     // stop camera when app is not active.
@@ -469,7 +498,7 @@ void Backend::updateUserProjectList()
         return;
     }
 
-    qDebug() << "Fetching available project list for user: " << userHash;
+    qDebug() << "Fetching available project list for user:" << userHash;
     QJsonArray projectList = m_serviceConnector.fetchUserProjectList(userHash);
 
     if (projectList.isEmpty()) {

src/serviceConnector.cpp

@@ -53,13 +53,13 @@ QByteArray ServiceConnector::fetchResource(const QString &url, const bool quite)
     QObject::connect(reply.data(),
                      &QNetworkReply::downloadProgress,
                      this,
-                     [&](qint64 bytesReceived, qint64 bytesTotal)
-                     {
-                         float percentage = roundf((float)bytesReceived / (float)bytesTotal * 100);
-                         qDebug() << "Download progress" << QString::number(percentage) << "% -" << QString::number(bytesReceived) << "/" << QString::number(bytesTotal);
+                     [&](qint64 bytesReceived, qint64 bytesTotal) {
+                         float percentage = roundf((float) bytesReceived / (float) bytesTotal * 100);
+                         qDebug() << "Download progress" << QString::number(percentage) << "% -"
+                                  << QString::number(bytesReceived) << "/"
+                                  << QString::number(bytesTotal);
                          emit downloadProgress(percentage);
                      });
-
     loop.exec();
 
     if (reply->error() != QNetworkReply::NoError) {
@@ -98,6 +98,7 @@ QJsonArray ServiceConnector::fetchUserProjectList(const QString &userHash)
     auto reply = fetchResource("https://designviewer.qt.io/api/v1/qmlrc/list/" + userHash
                                    + "?key=818815",
                                true);
+
     if (reply.size() == 0) {
         return QJsonArray();
     }