Re: [Algorithms] portal engines in outdoor environments

[gl <gl...@nt...>]

As I understand it, the idea with delayed z-testing is that whilst it's
horribly slow to get 'did this primitive I just tried to render get totally
z-rejected?' feedback from the card instantly (due to deep pipelining going
on), it's reasonable to get that info back a few frames late without
stalling anything.

The idea is to have that info determine your objects' LOD, ie. you render
your object with a low LOD by default, unless you find out that thing is now
visible, when you can bump up the tri count.  As the data is delayed, there
will be a change from low to hi LOD, but as we're only talking a few frames
(I believe), this shouldn't be all that noticable.  Note that you can't
simply avoid drawing the object, due to the delay - otherwise, it would
suddenly appear, a few frames later than it should.

In fact, my contention is that if it's only as little as two or three
frames, the higher rates you run at, the less significant the delay gets, to
the point were you probably don't even see the LOD pop, or you might not
even need to render until you're told it's there.

Tom, how many frames exactly would we be talking about?
--
gl

----- Original Message -----
From: "John Ratcliff" <jra...@ve...>
To: <gda...@li...>
Sent: Friday, August 18, 2000 7:18 PM
Subject: RE: [Algorithms] portal engines in outdoor environments


> If you had the ability to ask questions of the zbuffer like "is this
> bounding volume visable?" (yes/no) in an extremely high speed fashion then
> you could do gross culling on an object by object basis using the zbuffer
> contents during the render stage.  Some of the old spanbuffer software
> renderers could do this, because it was a fairly cheap question to ask,
> especially relative to the time it took to software render an entire 3d
> model.
>
> But, since you can't ask zbuffers these kinds of questions it's a moot
> point.
>
> John
>
> -----Original Message-----
> From: Ignacio Castano [mailto:i6...@ho...]
> Sent: Friday, August 18, 2000 1:06 PM
> To: gda...@li...
> Subject: RE: [Algorithms] portal engines in outdoor environments
>
>
> Tom Forsyth wrote:
> > I agree - it's a nightmare case for geometric occlusion. Delayed
> Z-visiblity
> > is our only hope. A shame we've been waiting two DX versions for it, and
> > it's going to miss this one as well.  Grrrrrrr. So while we have fancy
> > vertex shaders that nothing on Earth supports, we don't have API support
> for
> > something that even crusty old hardware like Permedia2 and Voodoo1
> supports.
> > Life... don't talk to me about life. :-)
>
> what do you mean with 'delayed Z-visibility'? could you explain that a bit
> more?
>
>
> Ignacio Castano
> ca...@cr...
>
>
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