Re: [Algorithms] OpenGL LockArrayEXT ... workaround

[Brian S. <br...@gl...>]

you wrote:
> > are you sure 4096 is the maxium size for optimized compiled vertex arrays?
> > I just though it was 1024, since q3 uses 1K vertex buffers (according to
>Brian Sharp's conference).

My conference?

Any information I have on Q3A is pretty much hearsay from Brian Hook.  Or 
maybe you're referring to Brian Hook, not Brian Sharp?  We're more 
different than our last names: I never worked for id. ;-)

At 11:30 AM 8/25/00 +0800, you wrote:
>It depends on the accelerator generally. Remember Brian worked on the 3dfx
>ogl drivers, which may mean his 1k number was based on those, rather than
>other drivers. I think most of the T&L cards are 4/8k.

So first of all, I don't see any actual defined limit (in the 
EXT_compiled_vertex_array spec) to the number of vertices you can 
lock.  The original poster should have no problem locking 100,000 
vertices.  If it's an issue of what implementations optimize for, that's 
kind of lame to write to that, especially because that's totally volatile 
and will probably change in most drivers before you ship.

In the existing 3dfx driver, at least, it'll optimize whatever you throw at 
it.  Sure, that's transformation happening on the CPU, but it guarantees 
that you don't end up retransforming verts.

The downside to that is the hypothetical case where someone locks a 30 
million vert array, and the driver allocates a ton of memory.  It can't be 
any more than the app already has allocated, but it's nonetheless potential 
for a lot of memory allocation.  So for future work it's being donw a 
different way, but it won't "not optimize" the arrays if they're over some 
size.

I'm not really sure what the motivation would be for a driver to not 
optimize arrays over a certain size.  I mean, they could only pretransform 
a set number and treat any more as regular verts to be 
transformed.  Hmm.  Especially if it's a hardware T&L implementation, where 
you'd obviously want to have a tiered caching system in the driver already, 
capable of locked arrays on the host bigger than your hardware cache.  I'm 
confused.

So, what was the original poster asking about?  Why couldn't he lock all 
his verts?  A driver crash?  A slowdown?  A spec misreading?

-Brian
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