[osg-users] Some yes/no questions about VBOs

David Spilling david.spilling at gmail.com
Wed Jul 2 05:43:18 PDT 2008


Dear All,

I have a few VBO related questions; a few quick yes/no answers would be much
appreciated to stop me going down dead ends...

I attach a vertex array, texcoord array and normal array to a Drawable,
which is using VBOs. From the code, I can see that calling dirty() on any of
the arrays dirties the entire VBO.

1) I can't quite understand all of the BufferObject code, but just to check,
it looks like all three arrays are dumped into one large contiguous buffer
(i.e. one single bufferID). Is that correct?

If(1) is true, and it's just one large buffer:

2) Am I right in thinking that limiting the upload to one of the arrays
would involve extending BufferObject to use glBufferSubData, as it isn't
currently supported?

3) Can you set the stride of each buffer object (i.e. to support
interleaving the arrays)? I can't see anything like glVertexPointer
anywhere.

4) More generally, is there any (easy) way to attach several BufferObjects
to a Drawable, such that you could separately dirty() vertex, texcoord or
normal without having to upload the others?

If (1) is false, and each array has a different buffer object/ID,

5) Is there an obvious way that I've missed for dirtying just one of the
arrays in the VBO space?

Thanks,

David
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