On Wed, 2009-03-11 at 10:29 -0700, Ian Romanick wrote:
>
> The subrange flush is, IMO, not well specified. The spec allows two
> different behaviors that will give potentially different results to apps.
>
> 1. Flush the subrange immediately when glFlushMappedBufferRange is
> called. I believe this is what Apple implements for
> glFlushMappedBufferRangeAPPLE (see
> http://www.opengl.org/registry/specs/APPLE/flush_buffer_range.txt)
>
> 2. Collect marked subranges and flush on glUnmap. This seems like it
> would be the more sensible implementation for the existing memory
> managers in Mesa.
We've interpreted it as 2. Actually, we try to delay the actual flush
until it get's used.
> Peering into my crystal ball, I suspect the restriction preventing
> rendering while a buffer is mapped may eventually be lifted. If / when
> that happens, I can see apps moving to loops like:
>
> map()
> while () {
> generate_data();
> flush();
> draw();
> }
>
> unmap();
>
> > In the meantime, Jose & I have been experimenting with an asynchronous
> > mapping change to try and improve the behaviour of the vbo module & cut
> > down on the worst cases of excessive buffer usage. This is a simple
> > DONT_WAIT flag which allows the buffer_map operation to fail if it would
> > have blocked. This isn't exactly the same as the semantics from the
> > extension, but is somewhat memory-manager friendlier -- it doesn't allow
> > mapping a buffer which is currently being accessed by the GPU, for
> > instance...
>
> Is this an extra MAP_*_BIT for glMapBufferRange or does it only exist in
> the internal interface?
Internal interface only for now (in Mesa and in Gallium driver
interfaces).
Jose
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