[gameprogrammer] Re: Level of detail rendering

On 4/1/06, Leighton Haynes <dayta@xxxxxxxxxxxxxxxxx> wrote:
>
> Alan,
> As you've probably guessed, this technique is not new, it's been referred
> to as 'imposters' - a google search for something like imposters and
> rendering
> will get you various papers on the subject :) Not sure who was the first
> to
> use it.
>
> As you've guessed, for objects suitably far away, you can get away with
> updating them fairly infrequently (also remember, that even updating it
> once a second at 60fps cut's the amount of rendering of them by 60 (minus
> all the copying to texture/billboarding overhead). From memory, MS Flight
> Sim used them for clouds, and had the fairly unorthodox technique of using
> a software renderer, rendering the clouds->textures entirely using spare
> CPU cycles.
>
> No but from what I understand this is a LOD for extremely large models,
say terrian. I don't think that an impostor for a mountain has been done
yet, and personally I think I know why: how to know when to make it a
billboard? I don't want half of my mountain to become a billboard making the
rest seem slightly broken, it would be nicer if it did the impostor for
areas of the terrain instead of the whole thing.
Hmmm I got an idea from a map. What if the game created "figures" that
represent diferente heights, and each area actually represents an actual
height that area has, of course it would be a gross simplification.
Depending on the height diferences the LOD may decide to either draw it or
not. Say if the object is of the same distance it would be at a much shorter
image. If the change is positive, in this case a mountain, depending on the
size it would draw it a diferent sizes (each time with less detail). At a
certain distance where the mountain doesn't change of angle in a big time
you could use an impostor to replace the mountain.
There are various problems with this:
A. What if I go around a mountain keeping the impostor distance? How would
the game realize I just changed the angle a bit? When needed it could
upgrade the billboard, but
A1. what if I'm moving so fast that I change the angle really fast? We can't
do with tree's making a billboard out of two crosses (it's too big): we have
to render the mountain from that angle. It would actually use more memory to
handle the impostor than just render it. Maybe it the game had a "max speed"
variable that was used to calculate how far the billboard tecnique can be
used considering the fastest the camera can move at any moment. (It could
change gradually if there is acceleration of some sort). So in any moment
that the billboard becomes actually more of a hassle it's turned off and
instead less detail is used.
B. What about depresions? Say if I'm infront of a depresion that just drops,
a ridge, I couldn't see the depresion, but if it where on an angle.. and
because of the simplification of the actual levels of the grounds (the area
just represents the average height) one could actually see the fall from
quite close. Maybe nothing can be done for this, maybe you think something I
didn't.

Is this what you where talking about? I have no idea about this but it
sounds interesting..

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