Backward LOD? Sculpties get mangled CLOSE to them.

I'm baffled.

I've got a few sculpties that the viewer (Windlight or regular one) mangles when I get CLOSE to them. The funny thing is that this doesn't happen all the time. A few hours later they might look perfectly OK. Next day: Same problem reappears without me having done any changes.

Tried to delete the cache already: problems stays. The effect seems to happen to other people watching these sculpties, too, I asked some friends.

The attached picture shows this effect - the last 3 "fluff" sculpties in the row to the left get mangled as soon as the camera gets close enough for the most detailed LOD level.

The effect can happen to any or none of these 3, depending on how SL feels. Or on the moon vector. Or Philip Lindens biorhythm. Or whatever

Anybody experiencing the same thing?

-L

I've seen this a couple of times, but not recently.

Pure conjecture: the sculpty mesh switches to a higher LOD before the sculpty texture MIP switches. Or something like that using SL specific 3D engine lingo.

I'll add some conjecture of my own. Perhaps the sculpt map image is blurring, the way clothing textures sometimes blur. I don't know what causes that, or why when it strikes it seems to stick stubbornly to certain garments for a period of hours or days, even after relog and cache-clearing. But it does happen from time to time.

I've never seen the sculpty problem you're describing, but I've certainly seen the clothing thing, and the behavior sounds similar. But that doesn't mean it's actually the same thing, of course, only that it might be.

To further guess, I'd submit that perhaps the reason I haven't encountered the problem is that maybe I build my sculpties differently than you do. I tend to overlap vertices a lot, to make things as LOD-proof as I can. It stands to reason that that approach could maybe also prevent this problem, whatever its cause might be.

The downside is you don't have as much detail to play with, but since you have to get eyeball-bleedingly close to see full sculpty detail anyway, I don't really see it as a problem.

Anyway, as I said, I'm just guessing here. Sorry I don't have any better answers for you.

Haha. Chosen, it sounds like we are actually thinking the same thing here. I think I've seen the texture blur you speak of. It looked to me like what happens when a lower image MIP map level is displayed than the model LOD level would require to look good. I just used incomprehensible gibberish to explain I guess. Lemme have a second try at this.

MIP (an acronym for some fancy Latin words) mapping is like model LOD, but for images. Just like you don't need 3,000 vertices in memory to render something that will be 4 pixels in the viewer, you don't always need all 65,536 pixels of a 256x256 texture in memory to display the texture of that 4 pixel big object.

If a lower MIP map image is being used at a higher LOD level, it will look blurry as fewer pixels get interpolated for the texture of the higher resolution object. I assume that LL uses the same sort of tricks for sculpy maps as well and this would definitely affect how the map displaces the verts of a higher resolution sculpty.

More info on MIP mapping: http://en.wikipedia.org/wiki/Mipmap

Like I said in the first post though, this is pure conjecture on my part.

There is also a lossless sculptie rendering bug. Are these sculpt maps perchance uploaded with the lossless option?

See:

http://jira.secondlife.com/browse/VWR-2404

And possibly related:

http://jira.secondlife.com/browse/VWR-2968

Thanks a bunch, Darien - seems like this is what borks my sculpties. I've uploaded them according to the lossless uploading caveats here:

/8/64/215869/1.html

...but that of course doesn't mean that the bugs you mentioned won't hit me under some unknown circumstances. Anyways, your Jira-links make me sleep better - it's obviously a viewer problem that hopefully gets fixed one day.

Thanks again,
-L

Leban, based on your description, I very much doubt your problem has to do with the issues in those jira links. If it were just artifacting from lossy compression, you'd likely see glaring problems at all levels of detail, not just from up close. And the problem wouldn't switch itself on and off the way you described; it would happen all the time.

In any case, LL has purported lossless upload to have been fixed many times now, but it keeps failing anyway. It's pretty ridiculous.

I only upload sculpt maps via primscript.exe, since I know it's reliable. It only works with Maya-generated sculpties, though, so if you're not using Maya, you won't be able to use it. I've read mixed reviews of SLImageUpload, more good than bad, if you want to give that a try.

Actually, thats exactly how it behaves, the rendering defect will switch on and off at different angles and distances. There is one sculpt in Cel Edman's latest SFT pack (http://www.slexchange.com/modules.php?name=Marketplace&file=item&ItemID=551412)
in which he included two versions, a lossless one that sometimes shows the defect, and a lossy one that always renders correctly. He recommends not using the lossless version for the time being, but provided it for the future when the bug is corrected. He may be a good resource to find out additional details.