Fixed crash associated with reparenting a QGLWidget

We need to make sure that we don't reset() the context when the
QGLWidget is being reparented, as that will lead to the QOpenGLContext
being destroyed and not recreated, leading to a crash in makeCurrent().

Also, don't destroy() the widget if it has not yet been created, as in
that case there's no ParentAboutToChange event sent.

Task-number: QTBUG-31016

Change-Id: I409fff94456802a80bd72b470a6fbaee87505baa
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Andy Nichols <andy.nichols@digia.com>

src/opengl/qgl_p.h

@@ -132,6 +132,7 @@ class Q_OPENGL_EXPORT QGLWidgetPrivate : public QWidgetPrivate
 public:
     QGLWidgetPrivate() : QWidgetPrivate()
                        , disable_clear_on_painter_begin(false)
+                       , parent_changing(false)
     {
     }
 
@@ -142,7 +143,7 @@ public:
     bool renderCxPm(QPixmap *pixmap);
     void cleanupColormaps();
     void aboutToDestroy() {
-        if (glcx)
+        if (glcx && !parent_changing)
             glcx->reset();
     }
 
@@ -153,6 +154,7 @@ public:
     QGLColormap cmap;
 
     bool disable_clear_on_painter_begin;
+    bool parent_changing;
 };
 
 // QGLContextPrivate has the responsibility of creating context groups.

src/opengl/qgl_qpa.cpp

@@ -362,6 +362,15 @@ void QGLWidgetPrivate::cleanupColormaps()
 
 bool QGLWidget::event(QEvent *e)
 {
+    Q_D(QGLWidget);
+
+    // A re-parent will destroy the window and re-create it. We should not reset the context while it happens.
+    if (e->type() == QEvent::ParentAboutToChange)
+        d->parent_changing = true;
+
+    if (e->type() == QEvent::ParentChange)
+        d->parent_changing = false;
+
     return QWidget::event(e);
 }
 

src/widgets/kernel/qwidget_qpa.cpp

@@ -263,10 +263,8 @@ void QWidgetPrivate::setParent_sys(QWidget *newparent, Qt::WindowFlags f)
     bool explicitlyHidden = q->testAttribute(Qt::WA_WState_Hidden) && q->testAttribute(Qt::WA_WState_ExplicitShowHide);
 
     // Reparenting toplevel to child
-    if (!(f&Qt::Window) && (oldFlags&Qt::Window) && !q->testAttribute(Qt::WA_NativeWindow)) {
-        //qDebug() << "setParent_sys() change from toplevel";
+    if (wasCreated && !(f & Qt::Window) && (oldFlags & Qt::Window) && !q->testAttribute(Qt::WA_NativeWindow))
         q->destroy();
-    }
 
     adjustFlags(f, q);
     data.window_flags = f;