[osg-users] ViewerQT destruction

Virginia Holmstrom v.holmstrom at ama-inc.com
Thu Jul 3 06:28:22 PDT 2008


I am afraid I cannot help with Qt 4. Much to our dismay we haven't been allowed to use it due to bureaucratic issues.

I did hope to use CompositeViewer originally. But I was unable to get CompositeViewer to work across multiple QT windows:


The osgViewerQt example pops all the views up in one Qt window. Our users need to be able to open and close the views independently.

Also, I can not use QOSGWidget because on WindowsXP, OSG2.2 or OSG 2.4, Qt 3.3.3 we get the following error:

Using QOSGWidget - QWidget + osgViewer creating the graphics context.
Windows Error #2000: [Screen #0] GraphicsWindowWin32::setWindow() - Unable to create OpenGL rendering context. Reason: The pixel format is invalid.

So that is why I am using multiple Viewers, which worked well for us until we tried to destruct them.

Thank you so much,

Hi Virgina,

I have compiled you on my system, compiling against QT4, and get the error:

error: 'WDestructiveClose' is not a member of 'Qt'
make[2]: *** [examples/osgviewerQT/CMakeFiles/example_osgviewerQT.dir/AdapterWidget.o]
Error 1
make[1]: *** [examples/osgviewerQT/CMakeFiles/example_osgviewerQT.dir/all]
Error 2
make: *** [all] Error 2

I'm not very familiar with Qt so don't know the best way to map this across to QT4.  Suggesstions?

As a general note, when you have multiple views of a single scene graph, the right tool to use is osgViewer::ComposteiViewer rather than Viewer as otherwise you end up with duplicated update traversals and out of sync frame stamps.  Having things work event driven does complicate things though, as CompositeViewer is designed around a having single frame call that updates all windows at one time.
Supporting the event driven model with CompositeViewer/Viewer better will something that we'll need to work on - this doesn't change the crash issue, but it's something to bare in mind for the future.


On Wed, Jul 2, 2008 at 6:59 PM, Virginia Holmstrom <v.holmstrom at ama-inc.com> wrote:
> Robert-
> I have modified AdapterWidget.cpp from the osgviewerQt example. Use with Osg 2.4, Qt 3.3.3. It is obviously much simplified from what I have but exhibits a similar problem.
> What I changed:
> 1. Created 3 ViewerQts instead of just 1 2. Added a destructor to 
> ViewerQt 3. Added the Qt::WDestructiveClose flag to the AdapterWidget, 
> which triggers the ViewerQt destructor to be called when the window is 
> closed
> How to use:
> 1. osgViewerQTd.exe cow.osg
> 2. Mine pops up cascaded, cow in each window 3. Close a window (middle 
> window works well for me) 4. Check remaining windows, cow will likely 
> have disappeard from one of them 5. If this didn't work, try closing 
> the other windows, or running again and closing the windows in a different order.
> Thank you so much,
> Virginia
> Hi Virginia,
> There is not much I can do without seeing the problem first hand.  Is it possible to recreate it by modifying the existing osgviewerQT example?  If so, could do this to effectively create a unit test for this particular usage case.
> Another possible route with solving this type of usage case might be to explicitly pass in the parent window when creating the graphics context, but leave it to the OSG itself to create the windows rather that QT.  I haven't personally tried this, but it should be possible, even if it requires a few tweaks to the OSG itself to enable it.
> Robert.
> On Wed, Jul 2, 2008 at 3:22 PM, Virginia Holmstrom <v.holmstrom at ama-inc.com> wrote:
>> Hello
>> I have been having problems with the destruction of my ViewerQT window and I was wondering if anyone could shed some light on the issue. I am seeing corruption in one view when another view is deleted (screen shot attached). We are using OSG 2.4 and Qt 3.3.3 on WindowsXP and Linux. Problems are reproducible on both platforms.
>> We are required to permit muliple views into the same scene, each in 
>> its own window with its own navigation. The user may open one or more views, close views at anytime, and open new ones. We have a set up similar to the osgViewerQT example shipped with osg, where our ViewerQT inherits from both osgViewer::Viewer and the AdapterWidget. We actually flipped the inheritance order from the example, so that ours looks like this: ViewerQT : public AdapterWidget, public osgViewer::Viewer due to compilation problems with the Qt moc'ing the other way around.
>> Note we are using QGLWidget, not QOSGWidget, and we use multiple ViewerQts instead of CompositeViewer due to problems discussed in thread http://lists.openscenegraph.org/pipermail/osg-users-openscenegraph.org/2007-December/005676.html. Hence our use of multiple ViewerQts is also similar to Enrique Parodi's implementation he provided in that thread.
>> We store a ref_ptr to the root node of our scene external to the ViewerQts.
>> osg::ref_ptr < osg::Group > _osgScene; This ref_ptr persists as views 
>> are opened and closed and is only released when the application closes. Each time a ViewerQT is created we pass it the scene using setSceneData. All ViewerQts get the same root scene node.
>> We started having a problem when we set the Qt::WDestructiveClose flag in our AdapterWidget, which triggers the following destructors to be called in this order on close:
>> ViewerQT
>> osgViewer::Viewer
>> osgViewer::View
>> osg::View
>> AdapterWidget
>> We normally perform cleanup of our own classes in 
>> ViewerQT::~ViewerQT, however we see the corruption when the ViewerQT 
>> destructor is empty as well! The AdapterWidget destructor contains 
>> _gw->getEventQueue()->closeWindow();
>> The easiest way to reproduce the problem is to open multiple windows, then close the first window(view), triggering its destruction. Frequently the last window will be corrupted. I use corruption for lack of a better term. Geometry may disappear, textures may disappear, osgText may become blocks, while other parts of the scene are still visible in their original form. We've also had problems with the background stars flipping to an opaque dome.
>> In the screen shot provided I closed the first window (hence blank space upper left) and immediatly as I did that portions of the scene disappeard from the last window (bottom right) and the text became blocks.
>> If I subsequently open a new window the scene usually appears normal.
>> I am not sure if I have a:
>> memory problem?
>> problem with the shared scene when ViewerQTs destruct?
>> problem in the GraphicsWindowEmbedded?
>> QT problem?
>> ???
>> I am very open to suggestions. ;-)
>> Thank you so much,
>> Virginia

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