diff --git a/src/widgets/kernel/qopenglwidget.cpp b/src/widgets/kernel/qopenglwidget.cpp
index a852d4a4747..a83884ca03a 100644
--- a/src/widgets/kernel/qopenglwidget.cpp
+++ b/src/widgets/kernel/qopenglwidget.cpp
@@ -791,10 +791,8 @@ void QOpenGLWidgetPrivate::initialize()
     // texture usable by the underlying window's backingstore.
     QWidget *tlw = q->window();
     QOpenGLContext *shareContext = get(tlw)->shareContext();
-    if (Q_UNLIKELY(!shareContext)) {
-        qWarning("QOpenGLWidget: Cannot be used without a context shared with the toplevel.");
-        return;
-    }
+    // If shareContext is null, showing content on-screen will not work.
+    // However, offscreen rendering and grabFramebuffer() will stay fully functional.
 
     // Do not include the sample count. Requesting a multisampled context is not necessary
     // since we render into an FBO, never to an actual surface. What's more, attempting to
@@ -804,9 +802,11 @@ void QOpenGLWidgetPrivate::initialize()
     requestedFormat.setSamples(0);
 
     QScopedPointer<QOpenGLContext> ctx(new QOpenGLContext);
-    ctx->setShareContext(shareContext);
     ctx->setFormat(requestedFormat);
-    ctx->setScreen(shareContext->screen());
+    if (shareContext) {
+        ctx->setShareContext(shareContext);
+        ctx->setScreen(shareContext->screen());
+    }
     if (Q_UNLIKELY(!ctx->create())) {
         qWarning("QOpenGLWidget: Failed to create context");
         return;
@@ -815,7 +815,9 @@ void QOpenGLWidgetPrivate::initialize()
     // Propagate settings that make sense only for the tlw. Note that this only
     // makes sense for properties that get picked up even after the native
     // window is created.
-    QSurfaceFormat tlwFormat = tlw->windowHandle()->format();
+    QSurfaceFormat tlwFormat;
+    if (tlw->windowHandle())
+        tlwFormat = tlw->windowHandle()->format();
     if (requestedFormat.swapInterval() != tlwFormat.swapInterval()) {
         // Most platforms will pick up the changed swap interval on the next
         // makeCurrent or swapBuffers.
@@ -918,9 +920,14 @@ extern Q_GUI_EXPORT QImage qt_gl_read_framebuffer(const QSize &size, bool alpha_
 QImage QOpenGLWidgetPrivate::grabFramebuffer()
 {
     Q_Q(QOpenGLWidget);
+
+    initialize();
     if (!initialized)
         return QImage();
 
+    if (!fbo) // could be completely offscreen, without ever getting a resize event
+        recreateFbo();
+
     if (!inPaintGL)
         render();
 
@@ -1371,7 +1378,7 @@ int QOpenGLWidget::metric(QPaintDevice::PaintDeviceMetric metric) const
         if (window)
             return int(window->devicePixelRatio() * devicePixelRatioFScale());
         else
-            return 1.0;
+            return int(devicePixelRatioFScale());
     default:
         qWarning("QOpenGLWidget::metric(): unknown metric %d", metric);
         return 0;
@@ -1422,7 +1429,14 @@ bool QOpenGLWidget::event(QEvent *e)
             d->reset();
         // FALLTHROUGH
     case QEvent::Show: // reparenting may not lead to a resize so reinitalize on Show too
-        if (!d->initialized && !size().isEmpty() && window() && window()->windowHandle()) {
+        if (d->initialized && window()->windowHandle()
+                && d->context->shareContext() != QWidgetPrivate::get(window())->shareContext())
+        {
+            // Special case: did grabFramebuffer() for a hidden widget that then became visible.
+            // Recreate all resources since the context now needs to share with the TLW's.
+            d->reset();
+        }
+        if (!d->initialized && !size().isEmpty() && window()->windowHandle()) {
             d->initialize();
             if (d->initialized)
                 d->recreateFbo();
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 37114449ba8..370ae2aed15 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -12229,10 +12229,9 @@ QOpenGLContext *QWidgetPrivate::shareContext() const
 #ifdef QT_NO_OPENGL
     return 0;
 #else
-    if (Q_UNLIKELY(!extra || !extra->topextra || !extra->topextra->window)) {
-        qWarning("Asking for share context for widget that does not have a window handle");
+    if (Q_UNLIKELY(!extra || !extra->topextra || !extra->topextra->window))
         return 0;
-    }
+
     QWidgetPrivate *that = const_cast<QWidgetPrivate *>(this);
     if (!extra->topextra->shareContext) {
         QOpenGLContext *ctx = new QOpenGLContext;
diff --git a/tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp b/tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp
index c7fca550e52..510576f6df7 100644
--- a/tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp
+++ b/tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp
@@ -61,6 +61,8 @@ private slots:
     void showHide();
     void nativeWindow();
     void stackWidgetOpaqueChildIsVisible();
+    void offscreen();
+    void offscreenThenOnscreen();
 };
 
 void tst_QOpenGLWidget::initTestCase()
@@ -572,6 +574,74 @@ void tst_QOpenGLWidget::stackWidgetOpaqueChildIsVisible()
     #undef VERIFY_COLOR
 }
 
+void tst_QOpenGLWidget::offscreen()
+{
+    {
+        QScopedPointer<ClearWidget> w(new ClearWidget(0, 800, 600));
+        w->resize(800, 600);
+
+        w->setClearColor(0, 0, 1);
+        QImage image = w->grabFramebuffer();
+
+        QVERIFY(!image.isNull());
+        QCOMPARE(image.width(), w->width());
+        QCOMPARE(image.height(), w->height());
+        QVERIFY(image.pixel(30, 40) == qRgb(0, 0, 255));
+    }
+
+    // QWidget::grab() should eventually end up in grabFramebuffer() as well
+    {
+        QScopedPointer<ClearWidget> w(new ClearWidget(0, 800, 600));
+        w->resize(800, 600);
+
+        w->setClearColor(0, 0, 1);
+        QPixmap pm = w->grab();
+        QImage image = pm.toImage();
+
+        QVERIFY(!image.isNull());
+        QCOMPARE(image.width(), w->width());
+        QCOMPARE(image.height(), w->height());
+        QVERIFY(image.pixel(30, 40) == qRgb(0, 0, 255));
+    }
+
+    // ditto for QWidget::render()
+    {
+        QScopedPointer<ClearWidget> w(new ClearWidget(0, 800, 600));
+        w->resize(800, 600);
+
+        w->setClearColor(0, 0, 1);
+        QImage image(800, 600, QImage::Format_ARGB32);
+        w->render(&image);
+
+        QVERIFY(image.pixel(30, 40) == qRgb(0, 0, 255));
+    }
+}
+
+void tst_QOpenGLWidget::offscreenThenOnscreen()
+{
+    QScopedPointer<ClearWidget> w(new ClearWidget(0, 800, 600));
+    w->resize(800, 600);
+
+    w->setClearColor(0, 0, 1);
+    QImage image = w->grabFramebuffer();
+
+    QVERIFY(!image.isNull());
+    QCOMPARE(image.width(), w->width());
+    QCOMPARE(image.height(), w->height());
+    QVERIFY(image.pixel(30, 40) == qRgb(0, 0, 255));
+
+    // now let's make things more challenging: show. Internally this needs
+    // recreating the context.
+    w->show();
+    QTest::qWaitForWindowExposed(w.data());
+
+    image = w->grabFramebuffer();
+    QVERIFY(!image.isNull());
+    QCOMPARE(image.width(), w->width());
+    QCOMPARE(image.height(), w->height());
+    QVERIFY(image.pixel(30, 40) == qRgb(0, 0, 255));
+}
+
 QTEST_MAIN(tst_QOpenGLWidget)
 
 #include "tst_qopenglwidget.moc"