On 7 Nov 2014, at 02:05, John Weeks <j...@wavemetrics.com> wrote:
> Can anyone tell me about QWindow::setTransientParent()? When building with
> Qt 5 I keep seeing warnings:
>
> void QWindow::setTransientParent(QWindow *) QWidgetWindow(0x118c39a10, name =
> "QWidgetClassWindow") must be a top level window.
>
> One situation where I see it is on Macintosh:
>
> Our application can make a 3D graph window that uses OpenGL calls to draw.
> The OpenGL context is implemented via a QGLWidget. The QGLWidget is
> contained in a QWidget that is itself contained in a QWidget that is
> (usually) a top-level window.
>
> I see the warning when calling new QMenu(QGLWidget *). Here's a (truncated)
> stack trace (GizmoWD is our class, of course):
>
> 0 QWindow::setTransientParent(QWindow*) qwindow.cpp 1131
> 0x10969ac1a
> 1 QWidgetPrivate::setParent_sys(QWidget*, QFlags<Qt::WindowType>)
> qwidget.cpp 10516 0x10898b528
> 2 QWidget::setParent(QWidget*, QFlags<Qt::WindowType>) qwidget.cpp
> 10375 0x108971b07
> 3 QWidgetPrivate::init(QWidget*, QFlags<Qt::WindowType>) qwidget.cpp
> 1179 0x10896fe3c
> 4 QWidget qwidget.cpp 1026 0x1089701a9
> 5 QMenu qmenu.cpp 1333 0x108b3468f
> 6 QMenu qmenu.cpp 1336 0x108b3460d
> 7 GizmoWD::init(char const*, int) GizmoWD.cpp 90 0x100cb58f9
> 8 doNewGizmo(GizmoWD**, char const*, char*, wDataClass*,
> wdChildInfo::hostRectType, WMRect*, int, int, int) GizmoBuiltInOps.cpp
> 279 0x100c81f7a
>
> In tracing into this, I see that QGLWidget requires a WinID. The QWindow *
> being passed to setTransientParent() is the QGLWidget. The QWindow whose
> setTransientParent() method was called is the QMenu.
>
> I haven't seen any obvious problems that I can trace to this, but maybe I'm
> missing something.
>
>
> I also see it on Windows in some other situations.
>
>
> My apologies for a somewhat vague and abstruse question. I'm trying to
> understand the warning, but I don't have an obvious place to start. Thanks
> for any light you can shed!
I can reproduce it with qtbase/examples/opengl/legacy/hellogl like this:
void GLWidget::mousePressEvent(QMouseEvent *event)
{
lastPos = event->pos();
if (event->button() == Qt::RightButton) {
QMenu m(this);
m.addAction("test item");
m.exec(event->globalPos());
}
}
and the warning is in
void QWindow::setTransientParent(QWindow *parent)
{
Q_D(QWindow);
if (parent && !parent->isTopLevel()) {
qWarning() << Q_FUNC_INFO << parent << "must be a top level window.";
return;
}
which is harmless, right? Have you actually seen any behavior problems? But
we shouldn’t emit needless warnings either. So I wrote up
https://bugreports.qt-project.org/browse/QTBUG-42464
QGLWidget is obsolete, because it has the disadvantage of requiring its own
platform window for the GL content to render into, which has caused various
problems over the years. QOpenGLWidget (new in Qt 5.4) simplifies some things:
Qt uses FBO tricks to composite the OpenGL content and the other widgets into a
single window. So you should probably try to switch from QGLWidget to
QOpenGLWidget.
setTransientParent just provides a hint that one window is a dependent of
another, so that e.g. a dialog is to be shown centered over the main window.
For a context menu’s popup window, maybe that should not be necessary at all,
actually, because it has to set its position to be right next to the cursor: we
can’t depend on the window manager to position it.
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