Fix software backend detection

QSG hasn't parsed and set the backend yet, so we do need to duplicate
the logic it will use later to make a proper detection.

Pick-to: 6.3
Fixes: QTBUG-103372
Change-Id: I542ef9f52dd2725d3ff6e17f9142786e43425ebd
Reviewed-by: Michael Brüning <michael.bruning@qt.io>
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

1 files changed, 21 insertions, 1 deletions

diff --git a/src/core/web_engine_context.cpp b/src/core/web_engine_context.cpp
index 390002519..e59415423 100644
--- a/src/core/web_engine_context.cpp
+++ b/src/core/web_engine_context.cpp
@@ -160,7 +160,27 @@ namespace QtWebEngineCore {
 
 static bool usingSupportedSGBackend()
 {
-    return QQuickWindow::graphicsApi() == QSGRendererInterface::OpenGL;
+    if (QQuickWindow::graphicsApi() != QSGRendererInterface::OpenGL)
+        return false;
+
+    const QStringList args = QGuiApplication::arguments();
+
+    // follow the logic from contextFactory in src/quick/scenegraph/qsgcontextplugin.cpp
+    QString device = QQuickWindow::sceneGraphBackend();
+
+    for (int index = 0; index < args.count(); ++index) {
+        if (args.at(index).startsWith(QLatin1String("--device="))) {
+            device = args.at(index).mid(9);
+            break;
+        }
+    }
+
+    if (device.isEmpty())
+        device = qEnvironmentVariable("QT_QUICK_BACKEND");
+    if (device.isEmpty())
+        device = qEnvironmentVariable("QMLSCENE_DEVICE");
+
+    return device.isEmpty() || device == QLatin1String("rhi");
 }
 
 bool usingSoftwareDynamicGL()