Simple Browser example: Fix startup flicker on Windows

Ensure the initial browser tab is added before show(), avoiding
the flicker of RHI switching.

Pick-to: 6.4
Change-Id: I0aaa5a4128f089bfc9ef68d25cab44da78962eb6
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

4 files changed, 16 insertions, 4 deletions

diff --git a/examples/webenginewidgets/simplebrowser/browser.cpp b/examples/webenginewidgets/simplebrowser/browser.cpp
index 551edcc81..c1f5ddd55 100644
--- a/examples/webenginewidgets/simplebrowser/browser.cpp
+++ b/examples/webenginewidgets/simplebrowser/browser.cpp
@@ -16,7 +16,7 @@ Browser::Browser()
         &m_downloadManagerWidget, &DownloadManagerWidget::downloadRequested);
 }
 
-BrowserWindow *Browser::createWindow(bool offTheRecord)
+BrowserWindow *Browser::createHiddenWindow(bool offTheRecord)
 {
     if (!offTheRecord && !m_profile) {
         m_profile.reset(new QWebEngineProfile(
@@ -32,6 +32,12 @@ BrowserWindow *Browser::createWindow(bool offTheRecord)
     QObject::connect(mainWindow, &QObject::destroyed, [this, mainWindow]() {
         m_windows.removeOne(mainWindow);
     });
+    return mainWindow;
+}
+
+BrowserWindow *Browser::createWindow(bool offTheRecord)
+{
+    auto *mainWindow = createHiddenWindow(offTheRecord);
     mainWindow->show();
     return mainWindow;
 }
diff --git a/examples/webenginewidgets/simplebrowser/browser.h b/examples/webenginewidgets/simplebrowser/browser.h
index 604c45820..dcee68c79 100644
--- a/examples/webenginewidgets/simplebrowser/browser.h
+++ b/examples/webenginewidgets/simplebrowser/browser.h
@@ -18,6 +18,7 @@ public:
 
     QList<BrowserWindow*> windows() { return m_windows; }
 
+    BrowserWindow *createHiddenWindow(bool offTheRecord = false);
     BrowserWindow *createWindow(bool offTheRecord = false);
     BrowserWindow *createDevToolsWindow();
 
diff --git a/examples/webenginewidgets/simplebrowser/doc/src/simplebrowser.qdoc b/examples/webenginewidgets/simplebrowser/doc/src/simplebrowser.qdoc
index 70d58c1e4..f45b362df 100644
--- a/examples/webenginewidgets/simplebrowser/doc/src/simplebrowser.qdoc
+++ b/examples/webenginewidgets/simplebrowser/doc/src/simplebrowser.qdoc
@@ -67,6 +67,9 @@
     \skipto main
     \printuntil }
 
+    To suppress flicker when switching the window to OpenGL rendering, we call
+    show after the first browser tab has been added.
+
     \section1 Creating Tabs
 
     The \c BrowserWindow constructor initializes all the necessary user interface
@@ -256,6 +259,8 @@
     \skipto /^class Browser$/
     \printuntil public:
     \dots
+    \skipto createHiddenWindow
+    \printline createHiddenWindow
     \skipto createWindow
     \printline createWindow
     \skipto private:
@@ -271,7 +276,7 @@
 
     \quotefromfile webenginewidgets/simplebrowser/browser.cpp
 
-    \skipto Browser::createWindow
+    \skipto Browser::createHiddenWindow
     \printuntil m_profile.reset
     \dots
 
diff --git a/examples/webenginewidgets/simplebrowser/main.cpp b/examples/webenginewidgets/simplebrowser/main.cpp
index d0ac175f6..477a8171b 100644
--- a/examples/webenginewidgets/simplebrowser/main.cpp
+++ b/examples/webenginewidgets/simplebrowser/main.cpp
@@ -31,8 +31,8 @@ int main(int argc, char **argv)
     QUrl url = commandLineUrlArgument();
 
     Browser browser;
-    BrowserWindow *window = browser.createWindow();
+    BrowserWindow *window = browser.createHiddenWindow();
     window->tabWidget()->setUrl(url);
-
+    window->show();
     return app.exec();
 }