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View Full Version : What's LOD-support?


|GG|Carl
06-20-2003, 08:42 AM
Maybe a noobish question, but I just want to know...
:)

Hindy
06-20-2003, 04:21 PM
LOD stands for Level of Detail... Which means in terms of player models that the further away the character is the less detail is needed so therefore the amount of polgons is cut down which in turn takes thestrain off your graphics card.

Wudan
06-21-2003, 04:19 PM
JK2's LOD system requires that player and weapon models have varying degress of lower polygon models included in the models file to reduce the impact the model has on your video card if it is further away.

When a modeller creates a model, he should include smaller polygon versions of the same model as additional "LOD" levels.

However, JK2's implementation of LOD is not 'true' LOD support, as it relies heavily on the artist to do something technical to save runtime (while the game is running) cpu cycles. I can pretty much guarantee that it is possible to create a more complex model and trick the game in to thinking that one is to be displayed further away, thus creating the reverse of the intended effect.

"True" LOD support would be calculated on the fly, and would result in lower FPS, in theory, if the CPU was able to handle the calculations without breaking a sweat. As far as the video card goes, it says "Whooopeeeeeee! Fewer Polygons!"

|GG|Carl
06-23-2003, 09:25 AM
:D

recombinant
06-23-2003, 05:10 PM
Originally posted by wudan
"True" LOD support would be calculated on the fly, and would result in lower FPS, in theory, if the CPU was able to handle the calculations without breaking a sweat. As far as the video card goes, it says "Whooopeeeeeee! Fewer Polygons!"

...and isn't that what Half-Life 2 is supposed to do? The've been talking about their "LOD System" so it must be an on-the-fly calculation system.

This would be sweet, since the modeler only would only have to worry about one version of his model, if I'm understanding correctly, since the engine will do all the dirty work, thus saving much of the artist's time...

:holosid:

Wudan
06-23-2003, 05:19 PM
At the same time, HL2 says it's a very scalable engine, and will run on a lightweight system.

There might be a setting to long the models in low poly or whatnot.

recombinant
06-23-2003, 05:23 PM
exactly. yeah that was the other attractive thing about it. kind of like a graphics bungie cord - it stretches & shrinks based on the capabilites of your hardware... it will be exciting to see what they've come up with!!!

(ov course, i'll prolly still be working on jodfmod, but that's another issue entirely...)

:D

CortoCG
06-23-2003, 06:07 PM
I believe the engines with progressive mesh or LODs on the fly have the same features that the polygon optimizing tools for max or any other 3d editors have.

Basically the tool starts collapsing vertices and edges using certain criterias, like excluding the borders of a mesh, keeping UV coordinates or using an axis of simmetry.

I think the engine calculates how many pixels does certain edge uses on the screen, and collapses it if that edge is within a treshold.

we'll know for sure as soon as the HL2 SDK is released. And that is before the game is released.

Wudan
06-23-2003, 07:55 PM
Originally posted by CortoMaltes
Basically the tool starts collapsing vertices and edges using certain criterias, like excluding the borders of a mesh, keeping UV coordinates or using an axis of simmetry.


Well, there are a number of publicly available algorythms for reducing polygons with emphasis on maintaining structure.

Essentially, first thing decided in almost all of them that I've read is to determine which edges are most important to the over all visual appearance.

CortoCG
06-23-2003, 08:49 PM
That's right, but even making LODs with those tools is not a hard and time consuming task, so I don't know at what point is better to have an on the fly LOD algorythm in the engine itself.

razorace
06-24-2003, 02:10 AM
I should note for all the codees in the audience that the Ghoul2 hit detection system normally uses the lowest LOD of Kyle's model to do hit detection for players in MP.

recombinant
06-24-2003, 03:01 AM
makes sense... the lowest common denominator.

it's probably more lean on the network hits too...

razorace
06-24-2003, 03:27 AM
It's because the Ghoul2 system has to run some complicated equations on each polygon for a ghoul2 hit scan. It's very CPU intensive. However, there's no network hit for ghoul2 hits.

Wudan
06-24-2003, 12:18 PM
Actually, some of the code included in Neo's package is from Ste Cork, at Raven, it's a quick and dirty way (it does not interpolate) to see where the hit zones are, alternatively, you could just run modview with Kyle on the lowest LOD with Interpolation off.

Corto, an on-the-fly LOD calculation algo is only as good as the values you give it. It may even be set per model, or per type of item - it depends on how you use it, but the main goal of reducing triangles rendered is met even by agressive culling methods, poly reduction is technically more efficient on the gfx card if you only reduce 1 triangle drawn, but the CPU would probably disagree.

CortoCG
06-30-2003, 02:47 PM
Anyway, I don't know how the LOD system work in JK2. My latest model has 3 levels of detail of 3391, ~2600 and ~2100 polys. But I can tell the difference when it gets far away from me while I'm playing. Can someone tell me at what distance does the LOD change?

CortoCG
06-30-2003, 02:47 PM

Infinity Blade
07-01-2003, 05:21 AM
Here's an image I made, for a tutorial I'm thinking about writing...

http://wat.midco.net/eggnog1/lodtest.jpg

It was made using an altered version of my Kyle that would change colors when the LOD changed.

The SP LODs are roughly the same as the MP LODs.....

Also, the next lower geometric detail setting in your game options moves the next lowest LOD up one.. so LOD 2 becomes 1, etc....

razorace
07-01-2003, 08:52 AM
That was a good idea, Blade. :)

CortoCG
07-01-2003, 11:55 AM
Good idea indeed. Thanks IB.

recombinant
07-01-2003, 02:32 PM
group hug time....

:D

Emon
07-01-2003, 11:48 PM
You've got to love the Serious Engine's (Serious Sam games) LODs. 32 LODs for models, calculated on the fly I think.

CortoCG
07-02-2003, 03:06 AM
Yes, indeed.

|GG|Carl
07-03-2003, 07:14 PM
Oh dear!
This seems to be quite complicated...