Hi All,
this is the other split thread that came out of the boost::function
start. Let's try to keep the subjects separate. I was tempted to restart
the thread, but that would lose the connection to the start discussion,
so I didn't do it.
Marcus Lindblom wrote:
>
> Yeah. Expression templates are kool. :) I suppose it will be better with
> C++0x and Concepts. However, clever use of +=/*= leads to efficient code
> too, without long compile times and horrible error messages.
At this point I would like to ask a general question for the users: how
many of you actually do vec/pnt operations on properties? Do you
dynamically change the values of whole vertex arrays? I'm not talking
about preprocessing, which is usually not that time-critical, but actual
work in the running program? How many create the geometry dynamically or
regenerate it on a regular basis?
My suspicion is that most people set up their scene once and then just
render it and move objects around, but I might be wrong.
>>> For instance, if you want peak performance, you should not have
>>> zero-initializing default ctors for vec/pnt classses.
>> that is true but changing this won't make us any friend ;-)
>
> I'd love you more if you did. :) But I think you're right. :)
We could have a define for it OSG_INSANELY_FAST_BUT_VERY_DANGEROUS or
something like it. ;)
> Also, perhaps it would make sense to make a Simd4f-class (that has it's
> MFSimd4f and GeoProp, and perhaps a Simd2d / Simd8ub, etc) for that
> extra over-teh-top speed. :)
The 4f part is the one that bothers me a bit. 90% of the vectors we use
are 3d, so either we have to do weird stuff like have x,y and z in
separate arrays or we have to tack on a 4th element that is not used.
Does SIMD really pay off if you have to do that?
> Anyway, I think I'm rooting at some way to separate these concerns a bit
> so that one could focus fully on each:
>
> * Default user-friendly lib with most code inside a dll
> * Expression template lib
> * SIMD stores (so that one at least avoids copies)
Can you give a little bit more info on 1 vs. 2?
Thanks
Dirk
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