Re: [Algorithms] Terrain performance comparisons

[Thatcher U. <tu...@tu...>]

On Jul 30, 2003 at 01:59 -0500, Jonathan Blow wrote:
> 
> That is not at all why I think shader LOD is important.  
> 
> The phenomenon I am worried about is that if you don't merge
> shaders, then there is an artificial limiter on how much you can LOD
> your geometry, because you can't merge triangles that use different
> shaders.  So what you end up with is, past a certain distance, a lot
> of small batches of triangles that just won't reduce any further.
> Your LOD is prevented from operating.  And it's really slow to
> submit all those batches to the hardware, due to all the context
> switching.

There's yet another (related) point I would like to make about shader
LOD: for decent fill-rate (and antialiasing), it's essential to have a
way to scale your texture accesses & shader computations with pixel
size.  For example, mip-mapping is a form of shader LOD.  But
mip-mapping basically is good for diffuse lighting on a flat surface,
it doesn't work quite right for normal maps etc.

I think to be compelling, the next frontier of geometric LOD has to
confront the shader LOD issue and unify it with geometric LOD.  In my
own LOD stuff in the past, I've handled this by using pre-baked
mip-mapped textures (w/ surface normals based on the hi-res geometry),
and unique texture mapping, which works for diffuse shading with
static lights and static geometry, but obviously that's pretty
limited.

-- 
Thatcher Ulrich
http://tulrich.com