[osg-users] Invalid GL buffer object

[Sajjadul Islam]

Hi forum,

I am getting the invalid buffer object with the following source snippet:


Code:

.......................
.......................

osg::VertexBufferObject* vbo = _m_clGeomRef->getOrCreateVertexBufferObject();

if(!vbo)
{
osg::notify(osg::FATAL)
<< __FUNCTION__ <<": " << __LINE__ << ": "
<< _m_clGeomRef->getName() << ": no buffer object found."
<< std::endl;

return false;
} // END OF - !vbo

//get the context id
unsigned int contextID = osgCompute::GLMemory::getContext()->getState()->getContextID();

//compile vertex buffer
osg::GLBufferObject *glBO = vbo->getOrCreateGLBufferObject( contextID );

if( !glBO )
{
osg::notify(osg::FATAL)
<< __FUNCTION__ <<": " << __LINE__ << ": "
<< _m_clGeomRef->getName() << ": no GL buffer object found."
<< std::endl;

return false;
} // END OF - !glBO

if( glBO->isDirty())
{
osg::GLBufferObject::Extensions* ext = osg::GLBufferObject::getExtensions( osgCompute::GLMemory::getContext()->getState()->getContextID(),true);

if(!ext)
{
osg::notify(osg::FATAL)
<< __FUNCTION__ <<": " << __FUNCTION__ << ": "
<< _m_clGeomRef->getName() << ": cannot find required extensions to compile buffer object."
<< std::endl;

return false;
}

//the following function call the glBufferData()
glBO->compileBuffer();

//unbind the buffer objects
ext->glBindBuffer(GL_ARRAY_BUFFER_ARB,0);
ext->glBindBuffer(GL_ELEMENT_ARRAY_BUFFER_ARB,0);

} // END OF - glBO->isDirty()

//avoid copy operation during osgCompute::MAP_HOST
memory._m_clLastModifiedCount.clear();

for( unsigned int d = 0; d < vbo->getNumBufferData(); ++d )
memory._m_clLastModifiedCount.push_back( vbo->getBufferData(d)->getModifiedCount());

GLuint objectid = glBO->getGLObjectID();

//create the vertex buffer from the gl buffer object
(memory._m_clDevBuffer) = clCreateFromGLBuffer(cxt->_m_clContext, // the valid opencl context
CL_MEM_READ_WRITE, // the memory has both the read and write access
objectid,
&errNum);

if( errNum != CL_SUCCESS )
{
osg::notify(osg::FATAL)
<< __FUNCTION__ <<": " << __LINE__ << ": "
<< _m_clGeomRef->getName() << ": unable to create opencl buffer object (clCreateFromGLBuffer): "
<< cxt->getErrorString(errNum) <<"."
<< std::endl;

return false;
}

.......................
.......................




As you can see that there is also one line of OpenCL code snippet where i am trying to create an OpenCL buffer from the OpenGL buffer object. But the buffer creation is not successful because the error string is telling that the
Code:
GLuint objectid = glBO->getGLObjectID();

is not returning the valid GL buffer object id or GL buffer object does not have an existing data store. I guess that i have to make it sure on the OSG side. AND this is where i seek your help.

Could you provide me with some hint to make sure that i got the valid GL buffer object and GL buffer object do have the existing data store. Please make some time to go through the code i have pasted above and let me know if i have missed something or at least where to look into.

Thank you!

Regards,
Sajjadul

------------------
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http://forum.openscenegraph.org/viewtopic.php?p=56774#56774





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[Sajjadul Islam]

Hi Forum,

It has been a while and i did not get any feed-back over my last post. I realized that i was not clear enough in my explanation. Let me try again.

I store the current graphics context and part of the code snippet shows that the current context is stored:


Code:

void Context::operator() (osg::GraphicsContext *gc)
{
if(gc->getState() == NULL)
{
osg::notify(osg::FATAL) << __FUNCTION__ << ": "
<< "osg::GraphicsContext must have a valid state. "
<< std::endl;
exit(EXIT_FAILURE);
}

//make this context current if not the current context
if(!gc->isCurrent())
gc->makeCurrent();

.................................

..................................

// Bind context to osgCompute::GLMemory
if( osgCompute::GLMemory::getContext() == NULL )
osgCompute::GLMemory::bindToContext( *gc );

.................................

.................................
}




As you can see that inside the realize operation i store the current context for later reference.

Now i use this context reference id to create the buffer object as follows:


Code:


......................
......................
//get or create a vertex buffer object from the geometry

osg::VertexBufferObject *vbo = _m_clGeomRef->getOrCreateVertexBufferObject();

//make sure that we have the vertex buffer object
//AND i checked the vbo creation is successful
if(!vbo)
return NULL;

......................................
......................................

//get the buffer object
// I HAVE THE PROBLEM WITH THE FOLLOWING STATEMENT.
// event though i get a valid pointer to glBO, i checked though the debugger that
//glGenBuffers is generating a buffer id with 0 value
osg::GLBufferObject *glBO = vbo->getOrCreateGLBufferObject(osgCompute::GLMemory::getContext()->getState()->getContextID());

//make sure that we have the buffer object
if(!glBO)
return NULL;






I have no idea why am i getting 0 value for the buffer id with glGenBuffers(..) call inside the constructor of GLBufferObject() - the class that came along with the repository.

I am using the context id that i have stored inside the realize operation.

Any hint on what might have went wrong ? Where should i look into ?

I shall be eagerly looking forward to your hint over this issue.

Thanks,

Sajjadul

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

http://forum.openscenegraph.org/viewtopic.php?p=56839#56839

[Sajjadul Islam]

Hi Forum,

I forgot to mention that i get a valid glBO pointer even though i have 0 buffer object id with
glGenBuffers(..)

Thank you!

Cheers,

Sajjadul

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

http://forum.openscenegraph.org/viewtopic.php?p=56840#56840

[Robert Osfield]

Hi Sajjadul,

I really don't know specifically what might be wrong with what you are doing, I can't make sense of the code snippets, it's the wider context that would probably illustrate what is going wrong.

The best I can do is mention that importance of only doing OpenGL calls from a thread with a valid graphics context, if you don't they you are likely to get errors or crashes simply because OpenGL requires the valid graphics context to be current.

Robert.

[Sajjadul Islam]

Thanks Robert,

I am not calling glGenBuffers() in my code. I am calling the following :


Code:

osg::GLBufferObject *glBO = vbo->getOrCreateGLBufferObject(osgCompute::GLMemory::getContext()->getState()->getContextID());

Since i am getting undefined behavior, i used the debugger to get inside the above statement and found that i am having the issue inside the GLBufferObject constructor.


Code:

GLBufferObject::GLBufferObject(unsigned int contextID, BufferObject* bufferObject, unsigned int glObjectID):
_contextID(contextID),
_glObjectID(glObjectID),
_profile(0,0,0),
_allocatedSize(0),
_dirty(true),
_bufferObject(0),
_set(0),
_previous(0),
_next(0),
_frameLastUsed(0),
_extensions(0)
{
assign(bufferObject);

_extensions = GLBufferObject::getExtensions(contextID, true);

if (glObjectID==0)
{
_extensions->glGenBuffers(1, &_glObjectID);
}

// OSG_NOTICE<<"Constucting BufferObject "<<this<<std::endl;
}




The immediate above snippet is from the BufferObject file that came along with the API.

And i found that _glObjectID is carrying the value 0 even after call:


Code:

_extensions->glGenBuffers(1, &_glObjectID);




I believe that 0 is not a valid value here.

Any more thoughts ?

Regards,
Sajjadul

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

http://forum.openscenegraph.org/viewtopic.php?p=56844#56844

[Robert Osfield]

Hi Sajjadul,

As I said I don't know what is going amiss in your code. Debugging this type of thing really requires a proper overview of all the code and ideally testable code.  This level of support is something I can provide.

Perhaps if you can't manage the wiring up of OpenCL and the OSG yourself you should look for 3rd party example codes that do it.  I haven't personally implemented OpenCL and OSG integation so can't help directly.

Robert.