[osg-users] Graphics context issues

[Ryan Thoryk]

Hi,

I'm trying to query GL parameters such as GL_VENDOR, which require an active graphics context to work. I looked another thread on this forum which explains how to do it, but it only works for a single-threaded viewer. I'm running the viewer in multithreaded mode, and am getting crashes due to context issues. Does anyone have an idea on how to do this?
Thanks

Example code. Usually crashes at the makeCurrent() line:

Code:

//get renderer information
osgViewer::ViewerBase::Contexts contexts;
viewer->getContexts(contexts, true);
contexts[0]->makeCurrent();
std::string vendor = (const char*)glGetString(GL_VENDOR);
Report("Vendor: " + vendor);
contexts[0]->releaseContext();




Ryan

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[Sebastian Messerschmidt]

Hi Ryan,

I guess your interfering with the currently set context. You're not
explaining where/when you call your snippet, but usually this would be
done inside a "realizeOperation".

A small example operation:

<code>
class TestSupportOperation: public osg::GraphicsOperation
{
public:

TestSupportOperation()
: osg::GraphicsOperation("TestSupportOperation",false){}

virtual void operator () (osg::GraphicsContext* gc)
{
OpenThreads::ScopedLock<OpenThreads::Mutex> lock(mMutex);
unsigned int contextID = gc->getState()->getContextID();

osg::GLExtensions* glext = osg::GLExtensions::Get(contextID, true);
if (!glext->isOpenGL20Supported)
{
std::cerr << No 2.0++ suppport available\n";
}
}
OpenThreads::Mutex mMutex;
};
</code>

In your viewer you simply add:

viewer->setRealizeOperation(new TestSupportOperation);


Hope that helps,
Sebastian

[Ryan Thoryk]

SMesserschmidt wrote:
> I guess your interfering with the currently set context. You're not
> explaining where/when you call your snippet, but usually this would be
> done inside a "realizeOperation".
>

I'll try your code. I was doing the code snippet right after a "viewer->realize()" call.

Ryan

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http://forum.openscenegraph.org/viewtopic.php?p=74292#74292

[Ryan Thoryk]

Your code works when my laptop is using Intel graphics, but when I switch to Nvidia graphics, the glGetString calls fail for some reason (maybe the GL context isn't switching?). Strange.
Switching the whole app to single-threaded works for both.

Ryan

------------------
Read this topic online here:

http://forum.openscenegraph.org/viewtopic.php?p=74297#74297

[Sebastian Messerschmidt]

Hi Ryan,

> Your code works when my laptop is using Intel graphics, but when I switch to Nvidia graphics, the glGetString calls fail for some reason (maybe the GL context isn't switching?). Strange.
> Switching the whole app to single-threaded works for both.

That's indeed strange. The snippet I provided might not do all the
necessary checks however. I use a similar piece of code in my projects
to ensure compatibility and it worked on a wide range of GPU/driver
combinations at least on Windows and Mac-Platforms.

Can you create a minimal _compilable_ example, so more people might
check what is wrong?

Cheers
Sebastian

[Ryan Thoryk]

SMesserschmidt wrote:
> Hi Ryan,

> Can you create a minimal _compilable_ example, so more people might
> check what is wrong?
>

Sure - I've attached an osglight-derived example. Compile with:

Code:

g++ -o osglight osglight.cpp -losg -lOpenThreads -lGL -losgUtil -losgViewer -losgDB




Ryan
[/code]

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http://forum.openscenegraph.org/viewtopic.php?p=74301#74301




Attachments:
http://forum.openscenegraph.org//files/osglight_161.cpp

[Sebastian Messerschmidt]

Windows tells me:

Screen 0:
Windows Error #170: [Screen #0]
GraphicsWindowWin32::makeCurrentImplementation() - Unable to set current
OpenGL rendering context. Reason: The requested resource is in use.

If I move your code into the callback it displays the correct
information however. Tested on Windows7:

Vendor: NVIDIA Corporation
Renderer: GeForce GTX TITAN Black/PCIe/SSE2
GL Version: 4.5.0 NVIDIA 372.90


Tested on Windows 10 (Nvidia Optimus) as well. The output in the console
is fine, but I see invalid rendering too.
Intel drivers aren't known to be a good reference for OpenGL
implementations, so I'd stick to Robert's advice and go for a
shader-based approach.

Cheers
Sebastian