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Descripton:
The patch does provide a new class PixelDataBufferObject which is capable of allocating memory on the GPU side (PBO memory) of arbitrary size. The memory can then further be used to be enabled into read mode (GL_PIXEL_UNPACK_BUFFER_ARB) or in write mode (GL_PIXEL_PACK_BUFFER_ARB). Enabling the buffer into write mode will force the driver to write data from bounded textures into that buffer (i.e. glGetTexImage). Using buffer in read mode give you the possibility to read data from the buffer into a texture with e.g. glTexSubImage or other instuctions. Hence no data is copied over the CPU (host memory), all the operations are done in the GPU memory.
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Compatibility:
The new class require the unbindBuffer method from the base class BufferObject to be virtual, which shouldn't break any functionality of already existing classes. Except of this the new class is fully orthogonal to existing one, hence can be safely added into already existing osg system.
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Testing:
The new class was tested in the current svn version of osgPPU. I am using the new class to copy data from textures into the PBO and hence provide them to CUDA kernels. Also reading the results back from CUDA is implemented using the provided patch. The given patch gives a possibility of easy interoperability between CUDA and osg (osgPPU ;) )
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I think in general it is a better way to derive the PixelBufferObject class from PixelDataBufferObject, since the second one is a generalization of the first one. However this could break the current functionality, hence I haven't implemented it in such a way. However I would push that on a stack of wished osg 3.x features, since this will reflect the OpenGL PBO functionality through the classes better.
"
"I was experiencing hard crashes of my application when using PBO's on
machines that don't support PBO's. I think osg incorrectly checks if
PBO's are supported.
I added a new method to the BufferObject::Extensions class which
returns if the "GL_ARB_pixel_buffer_object" string is supported. This
fixes the problem on my end. Machines without PBO support will
continue to work and machines with PBO support will still be able to
use it."
Note, this required adding a unsigned int context ID to the osg::isGLUExtensionSupported(,)
and osg::isGLExtensionSupported(,) functions. This may require reimplementation
of end user code to accomodate the new calling convention.
