RE: [Algorithms] Terrain performance comparisons

[Tom F. <to...@mu...>]

Not sure what you're getting at. There is nothing you can do to reduce
fillrate in a scene - objects have to be the required size - you can't
magically draw fewer pixels for them. What you can do is add more geometry
for "free", but if that's not useful geometry - who cares? Does a flat wall
benefit from more polys?

In general doing shader LOD to reduce fillrate isn't helpful - big things
consume lots of fillrate and pixel shader power with fancy shaders, but they
need to - they're big and important!

Small things can use much lower-quality shaders, but... they're small. You
don't save much fillrate by lowering shader quality becaue they cover few
pixels.

This was (sort of) the point I was trying to make. I think the point that
doing shader LOD allows you to do better batching and hierarchial LOD is far
more important.


Tom Forsyth - Muckyfoot bloke and Microsoft MVP.

This email is the product of your deranged imagination,
and does not in any way imply existence of the author.

> -----Original Message-----
> From: De Boer [mailto:be...@ii...]
> Sent: 30 July 2003 09:45
> To: gda...@li...
> Subject: RE: [Algorithms] Terrain performance comparisons
> 
> 
> Everyone should read the latest GD mag about fill rate bound 
> and transform
> bound geometry - "Stop Hitting the BOTTLENECK". Basically if 
> you have large
> walls you may have much more fill stuff happening then 
> transform. Often both
> can occur in parallel and so an object spends more time doing 
> fill, then it
> is fill bound.
> 
> If you have a large polygon that has 4 passes doing fancy 
> bump mapping,
> surely its the shader LOD that is more important since it will be fill
> bound. Of course if all your geometry is highly tesselated 
> and in one pass
> then yes geometry LOD is more important and more 
> "compelling". I recon in
> general shader LOD is just as important then geometry LOD (of 
> course in
> particular scenes one may be more useful then the other).
> 
> >>Shader LOD is less compelling to me than geometry LOD. If you have
> >>pretty much any sort of LOD - even static levels - then 
> you're going to
> >>be drawing (very) roughly constant-area triangles. So your
> >>vertex-processing load per pixel is roughly constant. And 
> obviously your
> >>pixel load per pixel is constant (excepting overdraw, which 
> you can't do
> >>much about using LOD - you need occlusion algos, which is 
> orthogonal to
> >>the problem).
> 
> -Ryan De Boer
> 
> 
> 
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_072303_01/01
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