Brett Johnson wrote:
|
| No doubt. Like I said, I could come up with a pathological dataset that
| would show a small (5%-10%) performance hit. But that's a real corner
| case on very fast hardware. I've never seen a dataset that came from
| a real application show any measurable performance degradation.
While I was at SGI, the mean triangle strip length observed in
customer applications was 4 vertices. State changes between strips
were common enough that they dominated overall rendering time for
nearly all apps. If you're lucky enough to be targeting John
Carmack's code instead of stuff like that, then life is much easier. :-)
| Yes it does, but the effect tends to be even smaller in cases where the
| hardware is comparatively slower than the CPU. ...
Given the advent of things like GeForce, I'd be betting on systems in
which the graphics is fast relative to the CPU. I'd also guess that
people believe CPU overhead is an issue, or we'd all be content with
the fine-grained vertex commands rather than vertex arrays.
| The possible performance gain is too small, and the added complexity and
| possible performance hit in the calling case is too large. ...
I believe the scheme I proposed allows an implementation with no
performance hit in the calling case and has complexity equal to or
less than dynamic slot assignment (because it minimizes changes to
existing drivers). Since it allows performance gains in state changes
for systems in which that's an issue, overall it seems like a better
tradeoff to me.
| Maybe this mailing list isn't the place to have this discussion? This is
| an area that I'm keenly interested in, but I don't think we're adding
| anything to the context (in)dependence discussion.
Good question. If everyone is convinced that context-independent
pointers can be supported with acceptable cost (for driver development
and for execution at runtime), then we're done; we can take the
details offline. If there's a sizeable group of people who are not
convinced, then we need to keep going a while longer.
Any votes?
Allen
