xcb: make it possible to disable gl integrations

By setting QT_XCB_GL_INTEGRATION to the special value "none", no plugins
will be considered for loading. This matches what eglfs does with
QT_QPA_EGLFS_INTEGRATION.

This allows widget or raster-QWindow-only apps to start up faster by not
spending time on plugin loading and potential initialization steps there.

Task-number: QTBUG-46765
Change-Id: Ifeec3548a9b58f619a18e0be75fe4a9f489677a9
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index 80c844e658..b8b665157b 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -532,9 +532,14 @@ QXcbConnection::QXcbConnection(QXcbNativeInterface *nativeInterface, bool canGra
     QStringList glIntegrationNames;
     glIntegrationNames << QStringLiteral("xcb_glx") << QStringLiteral("xcb_egl");
     QString glIntegrationName = QString::fromLocal8Bit(qgetenv("QT_XCB_GL_INTEGRATION"));
-    if (glIntegrationName.size()) {
-        glIntegrationNames.removeAll(glIntegrationName);
-        glIntegrationNames.prepend(glIntegrationName);
+    if (!glIntegrationName.isEmpty()) {
+        qCDebug(QT_XCB_GLINTEGRATION) << "QT_XCB_GL_INTEGRATION is set to" << glIntegrationName;
+        if (glIntegrationName != QStringLiteral("none")) {
+            glIntegrationNames.removeAll(glIntegrationName);
+            glIntegrationNames.prepend(glIntegrationName);
+        } else {
+            glIntegrationNames.clear();
+        }
     }
 
     qCDebug(QT_XCB_GLINTEGRATION) << "Choosing xcb gl-integration based on following priority\n" << glIntegrationNames;