[simmsimaging]

I'm not sure what is going on, and it's most likely something I'm doing, but I am noticing that some files exported from Max to Studio (exported as mxs) render very slowly compared to the same geo and materials re-imported into a brand new scene.

I copied the lighting (HDRI) and imported cameras and all and just fired up a new render. THe benchmark went from 5-15 for the first few SL to starting at 120.

Is there any known issue that might cause that?

/b

[Mihnea Balta]

We aren't aware of any problem which could cause that. Would it be possible to send us the two versions of the scene, so we can look into it?

[simmsimaging]

I was working away on the file for a few hours and have introduced a bunch of changes now - but I will save the two versions next time I get it to happen, or if I have some time to fabricate a file I will.


/b

[simmsimaging]

I PM'd you with a link to a pair of scenes that I think is showing the problem.

b

[Mihnea Balta]

You mention that you imported stuff from Max into the scene and then the slowdown started happening. What exactly did you import, and how was it exported from Max? The geometry seems to have changed and the objects are slightly moved as well, which could account for a difference in performance (although in this case it's weird, because it's a big difference).

[simmsimaging]

I imported the elements by exporting a few of them out of Max as a new .mxs file, and then imported the contents of that into Studio.

The parts were the large block part of the tag and the little diamonds I think too. I was playing with the geometry of those (penetrating or not) to see if that was making the difference, but did not seem to be.

b

[Mihnea Balta]

I'll forward the scene to the engine people so they can tell us why the second scene renders so much slower. It's odd indeed since the faster scene actually has more triangles and has extra render channels enabled. My first hunch was that the objects were exported with motion blur data from Max, but it doesn't seem to be the case. The second was interpenetrating objects, but if you say you've already checked that and makes no difference, it must be something weirder.

[simmsimaging]

I think the faster one actually has *more* interpenetration on the diamond objects. There is no motion blur enabled in the scene - at least nothing is moving and I haven't used it at all.

This seems to be similar to what was happening before for me (exported files slower at times, even without any changes that I was aware of) Hopefully you guys can figure it out.

Thanks /b

[simmsimaging]

Any progress or updates on this?

tks /b

[Mihnea Balta]

Not yet, sorry. The engine guys are looking into it.

[Mihnea Balta]

Apparently it's related to having a dielectric and an opaque material applied to the same object through a multimaterial (the gems with chrome fixtures). We're not sure yet exactly why it happens, but it might help to separate the fixture from the gem into separate meshes. I'll let you know when we find out more.

[simmsimaging]

Thanks for the update - much appreciated.

In this case it wouldn't be too bad, but that combined mesh was created for another piece that has hundreds of the diamonds scattered around a necklace thing, and it's done using Forest Pack Pro. I have to have the mesh collapsed to one object in order for it to work.

Hopefully it will be an easy fix for you guys.
b

[Mihnea Balta]

Scratch that - the multimaterial isn't the problem. The real difference is that in the faster scene, the gem is intersecting the fixture, while in the slower scene, there's a gap between them. I think light gets trapped in the small gap and takes a longer time to resolve. I'm not positive that this is source of the problem, but it appears so at the moment. One of the engine guys would have to confirm it.

[simmsimaging]

My understanding was that intersecting in Maxwell was a problem so I went in and fixed it. I'm pretty sure it was causing some issues with the refractions or caustics - can't remember now, but I know there was a reason I changed it to not intersect....


Thanks for keeping me posted on it.

[Mihnea Balta]

I've separated the gem from the fixture and made two scenes - one with a gap, one where they intersect. The one where they intersect renders about 3 times faster. I'll send you the scene by PM.

It's true that intersections can cause problems, but they also simplify the scene in this case. The thing is, if you model the object correctly, Maxwell will compute the correct solution, with all the bounces that happen inside the gap, which takes longer. If you push the gem into the fixture, the light trap is gone and the render time goes down, but you may see artifacts because the model is unrealistic.