[gameprogrammer] Re: Level of detail rendering

I'm sorry, I have no idea why you sent me this- I may program games, but I have 
no idea who you are.
  ----- Original Message ----- 
  From: Charlie Lobo<mailto:charlie.lobo@xxxxxxxxx> 
  To: gameprogrammer@xxxxxxxxxxxxx<mailto:gameprogrammer@xxxxxxxxxxxxx> 
  Sent: Saturday, April 01, 2006 10:36 PM
  Subject: [gameprogrammer] Re: Level of detail rendering


    A1: Yeah moving really fast would totaly own this technique.  I'm not sure 
how much support there is on the average computer for rendering to offscreen 
textures in video 
cards<http://www.qklinkserver.com/lm/rtl3.asp?si=92&k=video%20cards&st=1> these 
days but if it's out there, and assuming rendering to an off screen texture was 
as fast or faster than the screen texture, even if you had to draw every other 
frame you'd be using half the rendering power needed for this object.  In a 
worst case scenario, youd be re-rendering the distant object every frame which 
would suck but umm...maybe like you said, you could keep track of how often an 
object was being rendered and if it was too often, make it revert to some other 
LOD technique (: 

    In fact, i bet instead of making this all based on distance, to see if 
something should become a billboard instead of a model, you could just see how 
fast it updates ::shrug:: what do you think, good or bad?  One thing that would 
sure suck would be if a player stood still so that everything became a 
billboard then started moving again, would there be some cpu lag spike as it 
switched back to models? hmm :P 

  That sounds like a good idea, in the worst case scenario it would only render 
a frame (when it realizes the object is updating really fast) and then reverts 
to billboard (if the player slows down or it stops). But if the player is 
static not everything is made into a billboard, close objects still remain 
their 3-d detail). Moreover the programmer could have the chance to choose when 
to turn the billboard on or off, in case he/she wants to use another tecnique 
or knows there there is going to be alot of changes. 

  For the mountain LOD here are some ideas I've noticed seeing real mountain 
from far and close (the city is called Monterrey (Mountain King), that should 
give you an idea about how many mountains are over here). When seen from a 
certain distance trees become blurry green (making to texture, that's been 
done). But farther away they actually look blue(in case you haven't noticed the 
air is blue, and it actually works like fog at really high distances) and not 
only that, but slowly the sense of color disapears and only tones of light blue 
appear (convert to grayscale?). Details on ridges and so on from far could also 
easily be kept with a bump-map since the mountain is so far away the illusion 
will be kept but the polygon count is lowered. I don't know how much of these 
has been already done (but I know somethings have). 



    B: Ooo you are sooo correct. Well actualy because the drop is close to you, 
it *should* render in 3d and do LOD to a certain point and if the drop was 
really far, maybe use a billboard past that point.

    What i was picturing for this was like basicly getting the effects of a 
"skybox" but make the skybox be rendered on the fly (well hopefully not very 
often).  Maybe it would be a simple matter of something like temporarily moving 
the camera 1/2 a mile in front of where the player is, rendering what it sees 
to a texture, and then making that the skybox (or skysphere?). 

    Do you think it would be acheivable w/ such a simple trick?  I was thinking 
maybe as you rotated your view around and you saw more of the "sphere" 
surrounding you, it could render those tiles on the skysphere and cache them, 
re-rendering only if something out there changed significantly, or after you 
moved enough to re-render it. 




  Yeah that would work really nicely, actually the guy at machall 
(www.machall.com<http://www.machall.com/>) did a trick very similiar to this, 
maybe later I'll find a more direct link to the post he made. The trick he did 
though was for blurring, and actually isn't much faster at all. He basically 
renders the frame, and then passes a plane, perpendicular tu the camera, at a 
certain distance and and puts the pre-rendered frame blurred as texture. The 
effect is that anything behind the plane appears blurred, anything infront of 
the plane covers the plane (as long as it streches to cover the screen from 
that distance). 
  The problem with making the thing into a sky box is that if a mountain moves 
to the impostor distance, the whole skybox would have to be redrawn, it would 
be much easier to just draw the mountain and put a billboard for that mountain. 
  Now that I think of it, couldn't another impostor be added for a ridge, be it 
far enought? Even if I'm in a mountain, it's just about calculating the angle 
that the object is normally seen on and making the plane perpendicular to that 
angle (and positioned appropietly?) 
  So if I'm on a very deep ridge, the close border, and maybe the other side is 
actually 3d, but if I watch the bottom I'm actually watching a billboard, in 
the worst case scenario I would only see it one frame, in which case it was as 
if though the billboard wasn't used. Again bump-mapping would help create the 
illusion when I changed angle slightly. In the case I was in a mountain the 
floor could be a billboard, since it's so far away it barely appears to move, 
because the billboard terrain distance is so big there shouldn't be glitces on 
mountains. Other mountains could also be billboards, if they are far away 
enought. Because we actually billboard whole pieces of land, not just areas 
which are far away (again the whole idea of dividing the map into areas that 
represent big height changes), the whole mountain would be bill boarded or it 
would all be not billboarded. It would actually be nice the ability to force 
billboard certain things, the programmer may know that when the character is on 
mountain B there's no way to reach mountain A or change angle dramatically, so 
it's just billboarded (though later, when he leaves mountain B he may go to 
mountain A). And the ridge from the mountain, would also be a big billboard.. 
  Another thing about areas: when I'm at the base of a mountain, the peak may 
still be so far away (and the mountain be so big) that the peak may be 
billboarded, so even when on the mountain, it would be convenient to billboard 
certain parts of the mountain. 

    A downside tehre would be that the weak link in the chain (the most updated 
object) needed to be updated, everything would, so maybe pre-rendering 
everything to textures and then rendering onto the skysphere would be a better 
idea so that distant things would only need to be re-rendered as their 
threshhold was exceeded. 

  Again if every object is it's own billboard it maybe could change, if at most 
it would be a thing of every so many frames actually rerender the impostor, if 
we want to waste cpu in exchange for a very good change checker. The more 
attractive solution I think would be to have the programmer "reset" the 
billboard whenever he/she feels that something drastic enought to affect the 
model at large. Hopefully the programmers would find a solution that works for 
their specific issue, or they could just repeat the technique I just said up 
there (only it's their choice). 
  I don't even know if you understand what I'm saying :P

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