[osg-users] OsgViewer and Windows Forms

Todd J. Furlong todd at inv3rsion.com
Tue Nov 10 08:11:16 PST 2009

Thanks for the responses.

Ruben: That sounds like a robust way to handle threading issues.  We do 
something similar in VR Juggler based applications where one thread 
receives input but many have to render.

Andrew: Did you have to hook up a lot of UI events to get your scene to 
refresh during window relocation, etc?  We considered not rendering 
continuously to get around ToolTip transparency issues, but it seemed 
like it might be complicated to get the control to render when it needs to.


On 11/10/2009 10:56 AM, Andrew Burnett-Thompson wrote:
> Hi there,
> I'm doing something very similar - OSG hosted in .NET. The way I've done
> this is I have my render thread running in a loop and instead of
> rendering continuously, I have a Stack<RenderArgs> hosted in the OSG
> .NET control. Then if I want to render, I push a RenderArgs onto the stack.
> Inside the render thread, I check if there is an item in the stack, if
> so, pop it out and render.
> That way I have control over rendering (I only render when I need to in
> my app, as its a visualisation and doesn't need to run continuously).
> Also in the render thread, if there are no stack objects I will
> Thread.Sleep(1) to pause the render thread for 1ms (The minimum allowed
> time).
> This is just one solution. You could alternatively call frame directly
> and just use some object to handle the thread locking (Lock keyword in
> C# or Monitor::Enter/Exit in C++/CLI). Calling frame from within
> MainForm_Paint is not that bad an idea, I've donet his myself for
> DirectX visualisation applications before.
> Cheers,
> Andrew
> On Tue, Nov 10, 2009 at 3:48 PM, Smelik, R.M. (Ruben)
> <ruben.smelik at tno.nl <mailto:ruben.smelik at tno.nl>> wrote:
>     Hi Todd,
>     I've had the same choices to make for my .NET / OSG program. I'm not
>     sure whether or not the .NET timer / Invalidate is a stable
>     approach, FYI I'll just explain the solution I've chosen.
>     To avoid all the mutexes and threading issues, I went for a very
>     simple solution. A render thread loops to call frame() and a UI
>     thread processes user actions. Changes to the scene graph are made
>     in two steps:
>     * The UI thread sets a flag indicating what kind of change to the
>     scenegraph is required;
>     * Each iteration, the render threads checks (and clears) all flags
>     and makes the required scenegraph changes before calling frame().
>     Of course, depending on your application, this can be kind of
>     awkward (although you can replace flags with more detailed
>     "modification objects" containing loaded models etc.).
>     Kind regards,
>     Ruben
>     ________________________________
>     From: osg-users-bounces at lists.openscenegraph.org
>     <mailto:osg-users-bounces at lists.openscenegraph.org> on behalf of
>     Todd J. Furlong
>     Sent: Tue 11/10/2009 4:11 PM
>     To: OpenSceneGraph Users
>     Subject: [osg-users] OsgViewer and Windows Forms
>     I have a .NET Windows Forms application with 2 OSG-based classes:
>     1. A UserControl/OsgViewer based class, and
>     2. An OSG-based "engine" that handles file loading, scenegraph mods,
>     etc.
>     The .NET example from the OSG website gets the viewer initialized:
>     http://www.openscenegraph.org/projects/osg/wiki/Support/FAQ#HowdoIembedanOSGviewerina.NETcontrol
>     My question is: What is the best way to call the viewer frame function
>     in this application?
>     I have tried updating the viewer in a new thread.  It appears to perform
>     well, but it presents thread safety problems because my scenegraph
>     modifications (from the "engine") mostly take place in the UI thread
>     (button press events, etc).  I can simplify the engine code (avoid
>     mutexes around function calls) if I can get the viewer to update on that
>     thread.
>     To move the viewer onto the UI thread, I am calling the viewer frame
>     function in an override of the OnPaint method of the UserControl class.
>       I've created a Forms timer that periodically calls Invalidate on the
>     UserControl to make sure OnPaint  is called with some regularity.  Other
>     timer-related code insures that the Invalidate call isn't made at a
>     greater frequency than we expect the viewer to be able to render.  It
>     appears to be working OK, but I'm worried that this approach will be
>     fragile as we run this application on different systems with different
>     scene contents.
>     Comments or suggestions?
>     Thanks,
>     Todd
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Todd J. Furlong
Inv3rsion, LLC
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603-759-9035 mobile
888-588-0573 fax

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