Hi Fred,
what bandwidth are you trying to achieve? We've had no issues with
updating multiple osg Images from camera input with just a PBO attached
as per e.g.:
osg_image_buffer[i]->setPixelBufferObject(new
osg::PixelBufferObject(osg_image_buffer[i].get()));
where osg_image_buffer[i] is a ref_ptr to osg::Image.
jp
On 06/12/10 15:16, Fred Smith wrote:
Hi Robert,
Let's leave GPU -> CPU transfers aside. I don't mind if they are slow.
You usually have to use 2 PBOs.
If I use a single PBO to upload texture data to the GPU, performance will be
very low.
It seems to me I have two ways to do CPU -> GPU transfers efficiently.
1) Use 2 differents PBOs. Let glTexImage2D do its job with the first PBO, while
I'm loading up new data into the second PBO with the CPU.
2) Use 1 PBO and the method below (feedback?)
Code:
// Bind PBO
glBindBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, pbo);
Label1:
// Request new buffer data (third parameter = NULL)
// This call will return immediately. **The GPU will complete any transfer in
progress with the previous buffer data**.
// As far as the client side is concerned, the new buffer data is immediately
available.
glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_ARB, DATA_SIZE, NULL,
GL_STREAM_DRAW_ARB);
// Load up new pixels into the same pbo, but into its new buffer data
(requested above), not the previous one
glMapBuffer // returns immediately, because the GPU isn't doing anything with
the new buffer
updatePixels
glUnmapBuffer
// Issue asynchronous transfer to texture
glTexImage2D(......, 0);
goto Label1;
This method above which should work (I think!) will most likely not be
supported by OSG at all. I'll have to do things manually.
However perhaps I can resort to method 1 and do something by fiddling with two
osg::PixelBufferObject objects, two osg::Image objects, creating as many
osg::Textures as I want, alternating osg::Texture::setImage(image1) and
osg::Texture::setImage(image2), to be sure I am doing CPU and GPU work in
parrallel.
Thanks,
Fred
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=34554#34554
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